VI. THE AIRPLANE RADIO TELEPHONE

Electrical science was called upon to furnish marvels and prodigies indeed during the recent war as aids to the American arms, but in no respect did it respond in more successful and spectacular fashion than it did when asked to produce a wireless telephone system that would make possible the transmission of human speech to and from moving airplanes. It is doubtful if any other branch of science enlisted for war work produced any instrument or mechanism so far in advance of what was known before the war as the airplane wireless phone was in its class.

To be sure, we had the radio telephone some time before America entered the war or even before the war broke out in Europe in 1914. Ever since the scientists began experimenting with wireless electricity it has been axiomatic that, at least theoretically, whatever you can do with wires you can do without wires. And so following the development of the wireless telegraph came the production of the wireless telephone, and the invention had been so perfected in 1915 and 1916 that in the United States Navy's official test at the Arlington Station, across the Potomac River from Washington, human speech sent out by the transmitters there was heard simultaneously at the Eiffel Tower in Paris and at the Government's own wireless station in Hawaii.

But there is a vast difference between using the wireless telephone in the quiet of the radio rooms aboard ship or in the shore stations and using it amid the roar of the powerful engine propelling an airplane. The equipment, too, that had been used on the ground was altogether too cumbersome to go into the fuselage of an airplane.

As early as August, 1910, American genius had successfully accomplished wireless telegraph transmission from airplane to ground, and in October of the same year the idea of aerial fleet command by telephone was conceived and plans for its development discussed by Army officers on duty at the International Aviation Tournament at Belmont Park, Long Island. In 1911 a message was successfully transmitted from an Army airplane over a distance of 2 miles. In 1912 the Signal Corps had increased the distance to 50 miles. Two years later, in the Philippine Islands, a message had been successfully received on an airplane in flight over a distance of 6 miles.

In 1915 the Aviation Section entered upon a definite plan of development of aircraft wireless at the Signal Corps Aviation School, San Diego, Calif. This plan was based upon the Belmont Park idea and discussions, with the voice-commanded tactical air fleet as the ultimate goal. The airplane had changed from the pusher to the tractor type, with the noise of the motor of the latter driven back by the blast of the propeller into the face of the aviator. The airplane wireless problem was thus quite completely changed. Under these new conditions, however, the development was entered upon, and it has since been continuous. In October a spring-driven dictaphone was taken into the air and a record of speech made in the noise of the motor. This was contemporaneous with the successful long-range experiments in radio telephony at Arlington, referred to above. A study of this dictaphone record convinced the aviation officers that the idea of the radio telephone for airplanes was entirely practicable. Experiments during the fall and winter with various means of driving the wireless power plant resulted in a decision to develop the air fan as a source of power rather than the gear or belt system.

This development continuing through 1916, transmission by telegraph from airplane was accomplished up to 140 miles, means for receiving in the noise of the motor were worked out, and a message successfully telegraphed between airplanes in flight. The radio telephone was under construction, and in February, 1917, the voice was first transmitted by telephone from airplane to ground. Like Alexander Graham Bell's first wire telephone, the apparatus was crude. But the door was unlocked and ready to be opened upon the new field of development.

When on May 22, 1917, Gen. Squier, the Chief Signal Officer of the Army, called upon the scientists to develop at once an airplane telephone, he was not only introducing them into what was to many of them a new field, but he was asking them to produce what the science of Europe had been unable to create in nearly three full years of acquaintance with the successful ground system, although the needs of airplane fighting demanded this invention as they demanded almost nothing else.

It will thus be seen that when we began this development as a war measure we had a considerable basis of experience to work upon. The Army had established the foundation of operation on the airplane, made a study of the tactical requirements, and knew what it wanted. The Western Electric Co. in 1914 and 1915 had conducted extensive experiments with the radio wireless telephone at a ground station at Montauk, Long Island, and had played an important part in the long-range experiments at the Arlington station. There had been wireless voice communication before this time, but the apparatus and systems perfected at Montauk set the standard on which all subsequent development was built. The French Scientific Mission and other officers of the allies had arrived and enabled us to check up what had been done abroad and to confirm or modify our ideas of the tactical requirements.

At the conference with Gen. Squier in May was Col. Rees of the Royal Air Force of Great Britain; Col. C. C. Culver, United States Army, then a captain; and F. B. Jewett and E. B. Craft, respectively the chief engineer and the assistant chief engineer of the Western Electric Co.

At this meeting Gen. Squier outlined the future of the part the airplane was to play in the war, and pointed out how invaluable would be a successful means of communication between battle planes when flying in squadron formation. Mr. Jewett had received his commission as a major in the Signal Corps, and he was ordered to take charge of the work of developing radio communication for aircraft.

Capt. Culver had taken part in the 1910 experiments and discussions, and since 1915 had been conducting the Army development of airplane wireless at the aviation school at San Diego, Calif. He was detailed to work with Maj. Jewett and his engineers, bringing to their assistance the result of his experience and the point of view of the trained military man and the aviator.

The first development was carried on in the laboratories of the Western Electric Co. on West Street, in New York. Men and materials were drafted from every department of the company, and the laboratories were soon seething with activity. In a few weeks the first makeshift apparatus was assembled, and the first practical test of a radio phone on an airplane was made at Langley Field at Hampton, Va., less than six weeks after the Signal Corps had given the go-ahead. Three employees of the Western Electric Co. on that day established telephone communication between an airplane in flight and the ground. A few days later the first apparatus produced successful communication between planes in the air.

It is not possible here to go into a technical description of the wireless telephone. The most vital part of the apparatus, however, and the essential factor in airplane wireless telephone communication is a vacuum tube containing an incandescent filament, a wire mesh or grid, and a metal plate. By means of electrical current the wire filament is heated to incandescence. The tube has the property of receiving the energy of the direct current of a dynamo and, through the medium of the wireless antennæ, of throwing it out into space as a high-frequency alternating current. Such is the sending tube. A modification of the same tube picks up from the antennæ the high-frequency alternating vibrations from another sending apparatus and transforms them into direct current, carrying the sound waves of the human voice along with them.

The design of the radio apparatus itself was relatively simple for the experts who had undertaken the work, for the company had already developed some highly successful forms of vacuum tubes, and it was an easy matter for these technicians to assemble tubes with the necessary coils, condensers, and other apparatus of the transmitting and receiving elements and produce a system of such small compass that it could be carried on an airplane. But working this apparatus under ordinary conditions in the quiet laboratories and in a swift-moving and tremendously noisy airplane were two different propositions.

One of the first problems was to design a comfortable head set which would exclude all undesirable noises and admit only the telephone talk. A form of helmet was finally devised with telephone receivers inserted to fit the ears of the pilot or observer. Cushions and pads adjusted the receiver to the ears, and the helmet fitted close to the face so as to prevent as far as possible the transmission of undesirable sounds either through the ear passages or through the bony structure of the head, these bones acting as a sort of sounding board. The designers finally developed a helmet that solved this portion of the problem.

Not only was it necessary to exclude the roar of the engine and the rattle of the machine gun from the ears of the men receiving the radio communication, but it was also necessary to filter out these sounds from the telephone transmitter. Every person who has ever shouted into a telephone knows how sensitive the ordinary telephone transmitter is to extraneous noises. It requires no wide stretch of the imagination to hear in fancy how an ordinary transmitter would behave when beside the exhaust of a 400-horsepower Liberty engine. A brilliant line of experimentation conducted by one of the scientists at the laboratory resulted in a telephone transmitter or microphone which possessed the extraordinary quality of being insensitive to engine and wind noises and at the same time highly responsive to the tones of the human voice.

With the receiver and the transmitter perfected the scientists thought that the problem of airplane telephoning was solved; but nevertheless three months of hard work were required before the entire system could be adjusted and put in such shape that it might be considered a practical device for everyday use.

The question of weight was of utmost importance, and a structure that would adequately house and protect the delicate parts of the mechanism from the vibration and jars of flying and landing and at the same time not be too heavy for practical use on the plane was a difficult problem in mechanical design. Day after day the inventors took the mechanism up in flying machines and brought it back night after night for more work in the laboratory.

This was a period, however, of rapid progress. Officials appearing on Langley Field from time to time witnessed informal demonstrations of this development. In August Mr. Baker, Secretary of War, and Gen. Scott, Chief of Staff, listened to a conversation being carried on in the air, and some six weeks later Brig. Gen. Foulois witnessed a similar demonstration and from the ground directed the movements of the airplane in flight. The experimental apparatus had reached such a state of efficiency that on October 16, at Langley Field, communication by voice was carried on between airplanes in flight 25 miles apart and from airplane to ground over a distance of 45 miles. By September cables had been sent abroad telling of the progress made in this country on the development of this apparatus. Our officers abroad were skeptical and could not believe that this country could outdistance the scientists of the allies who had had three years of war experience to draw upon. By October the designers had brought the system to a perfection where they were willing to risk its use in actual war flying, and Col. Culver took to the American Expeditionary Forces in France several trunk-loads of the apparatus to acquaint those abroad with what had been done and to test the apparatus under service conditions. Meanwhile the development work continued in this country. Early in December the operation of the apparatus was exhibited in an official test at the Morraine Flying Field at Dayton, Ohio.

A large number of military and civilian officials not only of our own country but of the allies had been invited to witness this test. It must be remembered that at this time even those who had heard about the progress being made were skeptical of the possibilities of the successful adaptation of the radio telephone to airplane work. The designers of aircraft never look with favor upon additional equipment which may clutter up the machine with trailing wires and the like and possibly compel alterations in standard lines. The pilots, also, do not usually give a friendly reception to new equipment for their planes.

The exhibitors at Dayton planned to have two planes in the air at once, so that the officials might listen in on their conversation at a ground station located on the top of a hill near the flying field. By hard work the inventors got their equipment installed, and just at dark on the evening before the day of the trial one machine equipped with wireless went up into the air and held successful communication with the ground.

The next morning when the official party arrived the members viewed the apparatus in the planes while the inventors explained what it was expected to do. The visitors were then conducted to the station on the hill, where those who were putting on the show had rigged up a megaphone attached to the wireless receiver so that everyone could hear without putting on a head set.

The attitude of some of the officials, particularly those from the foreign nations who had had experience in war flying, was skeptical, if not bored. The planes left the ground, and when the machines had gone up so high that they were but specks in the sky the receiver began emitting the premonitory noises that indicated that the men in the planes were getting ready to perform. Suddenly out of the horn of the loud-speaking receiver came the words: "Hello, ground station! This is plane No. 1 speaking. Do you get me all right?"

Looks of amazement came over the faces of all those who had never heard the wireless phone in operation before. Soon came the signal from plane No. 2, and then the demonstration was on. Under command from the ground the planes were maneuvered over much of that part of the country. They were sent on scouting expeditions and reported what they saw as they traveled through the air. Continuous conversation was carried on, and finally, upon command, the planes came back out of space and landed as directed.

From that moment there was nothing but enthusiasm in all quarters for the radiophone upon airplanes. It was no longer a question whether the device would work or was any good, but a question of how soon the company could start manufacture and in what quantities the device could be produced.

The demonstrations Col. Culver had been conducting in France began, too, to bear fruit. Both the British and the French had developed experimental apparatus by this time and this was examined and tested. Then cablegrams began to arrive from abroad requisitioning the American apparatus in large quantities--convincing evidence that it had greater promise than any other.

But still difficulties were ahead, for at this stage the wireless telephone consisted of a few experimental parts built by hand. It remained a heavy task to standardize the equipment and perfect the multitude of designs and drawings that must be in existence before quantity manufacture could begin. All sorts of mechanical details slighted in the experimenting and taken care of by makeshift devices had to be worked out as practical manufacturing undertakings. It was another case of day-and-night work to put the mechanism into condition for production. The factory of the Western Electric Co. is in Chicago but its drafting rooms and laboratories are in New York. As soon as any detail was finally worked out the drawings were taken by messengers and rushed to Chicago where the work of producing the manufacturing tools had begun. Only the fastest passenger trains between New York and Chicago were patronized in this part of the development.

As every detail was perfected it had to be checked by actual test in the field, so that the company's engineers were almost constantly in the air. One of these experts made 302 flights himself; and a total of 690 flights, of a combined duration of 484 hours, was required in the experimental stage of the mechanism.

Immediately after the official trial in December the Government ordered thousands of sets of the radio telephone. In spite of the enormous detail involved in making ready for production, the first systems were turned out early in 1918, well ahead of the delivery of the airplanes in which they were to be used.

All through this development the designers had to confine their activities within limits set by the producers of the aircraft. This in itself created some puzzling problems. For instance, a constant current of electricity must be supplied to heat the filaments of the vacuum tubes and to operate the transmitter. A simple way to provide this current would seem to be to connect a dynamo with the driving shaft of the airplane engine, but the airplane constructors would not allow any such connection with the engine. Current could be supplied from storage batteries, but the planes were already loaded down with all the gear they could carry, and the use of heavy batteries was out of the question. Therefore it was the task of the phone designers to supply a dynamo plant that would not add appreciably to the weight of the plane. This was done by installing on the outside of the plane a wind propeller, which was driven by the rushing air and had power enough to turn the dynamo.

The dynamo must deliver a constant and unvarying voltage to the radio phone, if its operation is to be possible, yet a wind propeller on the airplane would be driven by air rushing by at speeds varying from 90 or 100 to 160 miles per hour, the latter figure being the speed of a diving plane. This meant that the wind propeller, and hence the armature of the dynamo, would revolve at a speed varying from 4,000 to 14,000 revolutions per minute. It would seem to be impossible to procure current at a constant rate from a dynamo varying so widely in its speed of operation; yet one of the experts engaged in this enterprise solved the problem, and the dynamo thereafter performed always in a most steady going and dependable manner.

Incidentally as a sort of by-product of the undertaking the special transmitter and helmet may be employed as a means of communication between the pilot and observer in a two-seated machine. When the helmet is used for this purpose, the wireless is not employed at all, but the head sets are connected by wires so that notwithstanding the fact that one can not hear himself talk because of the noise on the plane the pilot and observer can converse over the telephone with ease. Then at any time by throwing a switch they can connect themselves with the radio apparatus and talk with the men in another plane 3 or 4 miles away or to their squadron headquarters on the ground.

One good result of the airplane telephone was to speed up the training of aviators in this country and to make that training safer. But the primary object of the wireless phone was to make it possible for the leader of an air squadron at the front to control the movements of his men in the air. For this purpose extra-long range was not required, and the distance over which the machines could talk was purposely limited to 2 or 3 miles so that the enemy could not overhear the conversation except when the planes were actually engaged in fighting each other.

The Navy made use of the wireless telephone sets in the seaplanes, and here the range of the equipment was made greater. The Navy also adopted a modified form of the set for the 110-foot submarine chasers. The subchasers hunted the submarines in packs, and by means of the radio telephone the commanders of the boats kept in constant touch with each other, thereby greatly increasing the effectiveness of their operations.

Altogether there were produced for the Army airplanes about 3,000 combined transmitting and receiving sets of the radio telephone and about 6,500 receiving sets alone.

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VII. BALLOONS

When Stephen Montgolfier and his brother Joseph, in November, 1782, sent a sheep, a rooster, and a duck into the sky, lifted by a paper bag inflated with hot air, these Columbuses of ballooning could scarcely foresee the importance that their invention was to have in the great war 135 years later. To the humble observation balloon in France rather than to his dashing hero of a cousin, the airplane, must go the chief credit for that marvelous accuracy which long-range artillery attained during the great struggle.

The balloon itself was spectacular enough once its true character was known. The fact that the American production of observation balloons during our 19 months as a belligerent was a complete and unqualified success makes the story of ballooning in France of particular interest to the American reader.

After the animals of the Montgolfier barnyard had made their ascent, two friends of the brothers, M. Pilatre de Rozier and Girond de Villette, essayed to be the first human beings to take an aerial flight, ascending to a height of 300 feet and returning to earth sound of limb and body. Thereafter and until the great war in Europe the balloon remained the awe of the circus and country fair grounds and the delight of the handful of sportsmen who took up the adventurous pursuit; but, except for a limited use of captive balloons in our Civil War and in the siege of Paris, in 1870 and 1871, the balloon had no important military use.

The hot-air balloon never could have become of great value to armies. In the first place, it would descend when the balloon cooled off. This defect was overcome by the use of lighter-than-air gas. Moreover, the free balloon was subject to the whims of the breezes. To overcome this characteristic the balloon must be fastened by a cable or propelled by a portable engine. It was obvious, however, to military experts that a stationary observation post anchored thousands of feet in the air would be ideal in war operations; yet for all of this obvious need, until the great war military science had perfected nothing better than the spherical balloon. The spherical, anchored to a cable, bobbed aloft in the gales and zephyrs as a cork does on the ocean waves. Although there had been some experimentation with kite balloons before 1914, it was not until the great war had been in progress for some months that the principles of streamline shape were applied to the captive balloon; and the kite balloon, the well-known "sausage," made its appearance, to be the target for enemy aerial operations and the chief dependence of its own Artillery.

The term "kite balloon" effectively describes the captive observation balloon as we knew it in the war. It rides the air on the end of its cable much in the manner of an ordinary kite, and some of the early "sausages" even flaunted steadying tails such as kites carry. These principles applied to the captive balloon gave to its observation basket a stability unknown by the pioneer aeronauts under their spherical bags.

In the first stages of the war the Artillery relied principally upon airplanes for firing directions. But, while the airplane observers could locate the targets fairly well, they frequently lost touch with their batteries because of the difficulty of sending and receiving wireless or visual signals upon their swiftly moving craft. This disadvantage brought the captive balloon into use, gradually at first, but before the end of the war on a scale which had practically displaced the airplane as a director of gun fire. The balloon came to be the very eye of the Artillery, which, thanks to the development of this apparatus, reciprocated with an efficiency beyond anything known before in the history of warfare.

Sitting comfortably aloft, the observer in the kite balloon basket had the whole panorama of his particular station spread before him. His powerful glasses could note accurately everything transpiring in a radius of 10 miles or more. He was constantly in touch with his batteries by telephone and not only could give by coordinated maps the exact location of the target and the effect of the bursting shell, but could and often did supply most valuable information of enemy troop movements, airplane attacks, and the like. He was a sentinel of the sky with the keen, long-range vision of the hawk. He played a part less spectacular than the scout airplane with its free and dazzling flights, but his duties were not less important.

Nor did he suffer from ennui during his period aloft. When a kite balloon went up it became the subject of alert attention by the enemy, because it was up there on hostile and damaging business. Long-range high-velocity guns turned their muzzles on it, and planes swooped down upon it from dizzy heights, seeking to pass through the barrier of shell from antiaircraft guns and get an incendiary bullet through the fabric of the gas bag, an eventuality which meant the ignition of the highly inflammable hydrogen gas, the quick destruction of the balloon and perhaps of the luckless occupants of the basket as well, unless they could get away in their parachutes.

Only quick work could save the men in the basket in such a case. From the time the gas leaped into flame until the explosion and fall of the balloon there was an interval of rarely over 15 or 20 seconds. The pilot of the airplane could dodge and slip away from the guns, but not so the pilot of the kite balloon anchored to a windlass from 2 to 5 miles behind his own lines. He had to take what was coming to him without means of defense. He must carry on his scientific calculations unconcernedly and in his spare moments experience the questionable pleasure of watching on some distant hill the flash of an enemy gun trained upon him and then of waiting the 20 or 30 seconds for the whizzing messenger to reach him, the while he pondered on the accuracy of the enemy gunner's aim.

While the artillery on both sides paid considerable attention to the observation balloons, the fact was that few of them were brought down by direct shell hits. The diving airplane with its incendiary bullets was a far more deadly enemy to the balloon than the ground artillery. Certain pilots in all the air services made a specialty of hunting sausages, the nickname given to kite balloons because of their shape. In the 17 days between September 26 and November 11, 1918, our Army lost 21 balloons, of which 15 were destroyed by enemy planes and 6 by enemy shell. But it may be noted that our aviators and artillery exacted a toll of 50 German balloons in the same period and on the same front. Of 100 balloons lost at the front, an average of 65 were destroyed by enemy attacks and 35 by natural wear and tear.

The German general staff so strongly appreciated the work of the allied kite balloons that in its system of rating aviators it ranked a balloon brought down as the equal of one and one-half planes.

The average life of a kite balloon on an active sector of the western front was estimated to be about 15 days. Some of them lived only a few minutes. One American balloon passed unscathed through the whole period of American activity on a busy sector. While ordinarily five or six months of nonwar service will deteriorate the balloon fabric, there are many cases of useful service longer than this.

When the war broke out Germany is said to have had about 100 balloons of the kite type. France and England had few of them. The German balloon was known as the Drachen. Its gas cylinder of rubberized cotton cloth was approximately 65 feet long and 27 feet in diameter, the ends being rounded. To give it a kite-like stability in the air a lobe, which was a tube of rubberized fabric, of a diameter approximately one-third of the diameter of the main balloon, was attached to the underbody of the gas bag as a sort of rudder, which curved up around the end of the balloon. This lobe was not filled with gas, but the forward end of it was open so that when the balloon rose the breeze filled the lobe with air. The inflated rudder then held the Drachen in line. The lobe automatically met the emergency. In calm, windless weather the balloon needed no steadying and the lobe was limp. Let the gale blow, and the lobe inflated and held the nose of the Drachen into the wind. As a further stabilizer three tailcups, with mouths open to the breeze, were attached 10 feet apart on a line descending from the rear of the balloon. In a strong wind these helped to keep the contrivance from swinging.

The tail-cup was made of rubberized fabric, circular in shape, about 4 feet in diameter, and about 2 feet deep when inflated by the breeze. It looked like an inverted umbrella, and was attached to the tail end of the balloon for exactly the same purpose and with the same effect as the tail attached to a kite.

The Drachen type of balloon was still in the experimental stage here and in France and England when the Germans swept over Belgium. The Drachen balloon was clumsy and relatively unstable in high winds, yet its importance to the Artillery could not be ignored by the allies. The results of its work daily became more apparent. The first effort of the allies was to improve the Drachen to give it greater stability and permit it to go to higher altitudes. While this work was going on, Capt. Caquot, of the French Army, produced a kite balloon so superior that it quickly superseded what had been in use. Germany clung to the Drachen for a time, but finally abandoned it for the Caquot principles of design.

The earlier balloons of the sausage type had been merely cylinders with hemispherical ends. Now for the first time, in the Caquot model, appeared a captive that was sharply stream lined. Stream lines are lines so curved as to offer the least possible resistance to the medium through which a mobile object, such as a yacht, an automobile, or an airship, moves. The Caquot gas bag was 93 feet long, as compared with the Drachen's 65 feet of length, yet its largest diameter was only 28 feet, being but a foot thicker than the pioneer German type. The Caquot, as all balloons developed in the war, was made of rubberized cotton cloth. Its capacity of 37,500 cubic feet of hydrogen gas lifted the mooring cable, the basket, two observers, and the mass of necessary equipment, and in good weather the balloon could ascend to a maximum altitude of over 5,000 feet.

The principal innovation in the design of the Caquot balloon was the location of the balloonette or air chamber within the main body of the gas envelope. This chamber was in the forward instead of the rear part of the bag and along the bottom of the envelope. It was separated from the gas chamber by a diaphragm of rubberized cotton cloth, which was sewn, cemented, and taped to the inner envelope somewhat below the "equator" or median line from the nose to the tail of the gas bag.

When a balloon of the Caquot type is fully inflated, the diaphragm rests upon the underbody of the gas envelope, and there is no air in the balloonette. Then, as the balloon begins to ascend, at the higher levels the surrounding air pressure is reduced and the gas in the balloon expands. This expansion would normally burst the envelope when the balloon is at a high altitude, except for a safety valve which pops at the danger point and relieves the pressure. Also, when the balloon is anchored it gradually loses gas, since no fabric can be made entirely gas-tight. A flabby balloon in a gale of wind is dangerous to the men in the basket. This flabbiness might be expected to increase, too, as the balloon was hauled down into the heavier air pressures.

It was to overcome this flabbiness that the interior balloonette was first invented, but the new location not only accomplished this end but increased the stability, lessened the tension on the cable and allowed an almost horizontal position of the balloon itself. As the balloon rises the wind blows into the balloonette through a simple scoop placed under the nose of the balloon. This forces up the diaphragm and compensates for any loss of gas from the envelope above. If the day is calm and no air is driven into the balloonette, there is no danger from a flabby balloon anyhow, and hence no need for the air chamber. The thing is automatic.

The Caquot was equipped with lobes of rubberized fabric to act as rudders. These lobes, which were spaced equidistantly around the circumference of the rear third of the balloon, filled with wind when wind was blowing and there was need of rudders. In calm weather the lobes, particularly the two upper ones, hung loosely, resembling elephant ears. On account of this characteristic the Caquots were nicknamed "elephants" by the soldiers.

The Caquot maintained its stability without tailcups, and its construction caused it to ride nearly horizontally and directly above its mooring, regardless of winds. In this position it put much less strain on the anchoring cable than the old-fashioned sausage. This balloon has been operated successfully in winds as high as 70 miles an hour, so that apparently no gale could keep it on the ground.

When we went into the war both our Army and Navy were practically without observation balloons, and we knew little about their construction, although we had been watching the developments in Europe. One local National Guard organization had taken to the Mexican border a locally designed captive balloon, the gift of the Goodyear Tire & Rubber Co., of Akron, Ohio.

In April, 1917, the total production capacity of the United States was for only two or three military observation balloons in a month. But when the emergency came the various concerns whose plants were adaptable to this class of manufacture--the list including the Goodyear and Goodrich organizations at Akron, the United States Rubber Co., the Firestone Tire & Rubber Co., the Connecticut Aircraft Co., and the Knabenshue Manufacturing Co.--all joined wholeheartedly with the Signal Corps to solve our balloon problems.

One of these problems was the production of balloon cloth, for which there had never been any commercial call in this country. Such cloth obviously must be of cotton, for in cotton we had our largest supply of textile raw material. The cloth must be closely woven, smooth, and strong, to serve as a base for the rubberizing process. The standard balloon cloth should have a weave of approximately 140 threads to the inch both ways. In our vast cotton industry only a few mills had ever made such a cloth, and then only in small quantities. In fact we found only a few looms in existence capable of weaving such cloth, which must be from 38 to 45 inches wide. A single loom could turn out only an average of ten yards of this cloth in a day. Our balloon program was to call for millions of yards of high-count cloth, and this meant the construction of thousands of new looms, as well as the training of hundreds of weavers.

Naturally our cotton manufacturers were reluctant to undertake such a production, and their fears were justified when we found that the earliest deliveries of balloon cloth were frequently as high as 67 per cent imperfect. By the middle of 1918, however, the mills had so perfected their methods that the wastage amounted to only 10 per cent of the cloth woven. This wastage was largely caused by "slubs," knots, and other imperfections which prevented an even surface for rubberizing. Because of the lives which depended upon having perfect balloon cloth, the fabric was literally inspected inch by inch, and hundreds of men and women had to be educated especially in this inspection work.

The development of the new art of weaving balloon cloth was an achievement of no mean degree. In April, 1917, all of our cotton mills put together could produce only enough cloth to build two balloons a week. In November, 1918, our looms were turning out cloth sufficient for 10 balloons a day, an expansion in the industry amounting to 3,000 per cent in 19 months. This expansion proceeded at a rate that always kept us a little ahead of the military schedule. To produce 10 balloons a day the cotton mills had to turn out 600,000 yards of special cloth a month. In addition to the small army of weavers, this production called into service 3,200 looms.

Had the war continued another year, we would have reached our goal of 15 complete new kite balloons produced every day. Our complete project of balloons and dirigibles of all types called for a total output of 20,000,000 yards of balloon cloth. Had we reached the quantity production planned, we would have been able to supply not only our own needs but also all of the balloon needs of the allies in Europe. America had the raw materials necessary for the whole anti-German balloon program.

As it was, we supplied to France and England a considerable number of balloons when the materials shortage in those countries was becoming acute. The foreign users of this American made equipment reported that it was equal to the best European product. It should have been. No war material was ever manufactured more conscientiously than this. In addition to the painstaking care of the producers, from start to finish a large force of inspectors watched every step in the construction of each balloon, and when America sent a balloon to the front it was right for the work it had to perform.

The weaving of the cloth was but the first step in the production of the balloon fabric. The fabric of the balloon envelope resembles a sandwich in its construction, there being a thin film of specially compounded rubber between two plies of the cotton cloth. The outer ply of the cloth is cut on the bias. This method prevents any long straight tear down the grain of the fabric. The threads of the inner ply are set at an angle of 45° to those of the outer ply, thus distributing strain sufficiently to stop a "snag" practically where it starts.

The cotton cloth alone can not resist the seepage of gas, and, therefore, it is necessary to rubberize it, the rubber film being really the gas-resisting envelope. In this rubberizing process the cloth must be run through the spreading machine 30 to 35 times in order to build up the thin rubber film without a flaw in it of any kind. The outside ply of the balloon fabric is "spread," that is, painted with a rubber compound containing a coloring matter. This compound makes the fabric waterproof; it gives also protective coloring to the balloon when in the air, making it less visible to the enemy; and, finally and most important, this coloring absorbs the actinic rays of the sun which are so fatal to the life of rubber. In some of the fabric the rubber film itself was colored to withstand both the heat and ultra-violet rays, thus both protecting the rubber and reflecting the heat which would otherwise expand the gas in the balloon.

While in general we adopted the European standards of construction, we had to develop our own rubber compounds and cures as well as our various fabrication processes. The latest reports we received from the front stated that the American fabric not only was successful, but that it had an added characteristic which was a direct means of saving life. It was discovered that the American fabric burned more slowly than the European balloon fabric, giving the men in the observation basket more time to get away in the parachutes when the balloons were destroyed by hostile attack.

When we went into the war we had never built a windlass for a kite balloon. The ability of the American manufacturer solved this problem as it did almost every other problem in the development of war instruments. Steam was the motive power first used for windlasses, but before the fighting came to an end America had developed both gas and electric windlasses which were thoroughly efficient.

The best known type of gasoline windlass was that having two motors, one to turn the cable drum controlling the balloon's ascent and descent, and one for moving the windlass itself along the road. A record pull-down speed of 1,600 feet a minute, or more than three times the speed of the fastest passenger elevator, has been attained by the gasoline windlass.

The electric windlass, while pulling down the balloon at the slower rate of 1,200 feet per minute, was smoother in operation. The mobile windlass would move on a road under its own power at 20 miles an hour and could tow the balloon in the air at the rate of 5 miles an hour, or even faster if necessity demanded.

To play on the safe side at the start, we adopted a satisfactory windlass that had been developed in France. It was difficult to manufacture this entirely French machine with American materials and methods; yet James Cunningham, Sons & Co., of Rochester, N. Y., succeeded in obtaining a delivery of four complete windlasses per week.

In addition to this windlass we designed two of our own. One of these was the product of the United States Army Balloon School and was manufactured by the McKeen Motor Car Co., of Omaha, Nebr.; the other windlass was designed and manufactured by the N. C. L. Engineering Co., of Providence, R. I. Both were put into quantity production, assuring us a sufficient number of the best windlasses ever manufactured.

The first cable used to hold the balloon captive was approximately a quarter-inch in diameter, weighed 1 pound for each 8 feet of length had a breaking strength of 6,900 pounds, and was made of seven twisted strands of plow-steel wire, containing in all 133 separate wires. This cable, while it accomplished the original purpose, was early seen to have fine possibilities of development. The observers in the basket must be kept in constant communication with the Artillery and their own windlass and this communication could best and most efficiently be obtained by means of the telephone. The balloon telephone, as first used, was an entirely individual unit with its own separate cable from the basket to the ground. In this way communication was indeed established, but only at the cost of a decrease in possible altitude, increased cable resistance, and the necessity of an extra windlass for winding and unwinding the telephone cable.

Previous to the entrance of the United States in the war, preliminary experiments in France were being made with the view of putting the telephone wires in the center of the main cable, thus doing away entirely with the second cable and windlass. But there had never been developed a satisfactory cable of this construction. American inventiveness at the John A. Roebling Sons Co. and the American Steel & Wire Co. was set to work on this problem with the result that not only was a satisfactory cable developed but a steady production was attained, 50,000 feet per week being delivered regularly by the John A. Roebling Sons Co. alone. This new cable consisted of 114 separate wires of special steel besides the telephone center of 3 copper wires properly insulated and armored. The specifications demanded a breaking strength of 7,200 pounds while the actual test of the finished Roebling cable showed 8,250 pounds.

Another of the balloon problems was the supply of hydrogen gas. Before the war only a little hydrogen was used in this country, the element being a by-product in the manufacture of commercial oxygen. We met the additional demand for millions of cubic feet of hydrogen for our balloons by establishing Government gas plants and expanding privately owned plants already in existence. There were two methods of supplying hydrogen to our balloon units at home and abroad. One of these was by furnishing portable plants which would generate hydrogen at the place where it was to be used. The other was to take the hydrogen from the stationary plants, condense it by pressure in steel cylinders, and ship it to points of demand. By far the greater part of the gas which we used not only in this country but in France was produced at the permanent supply stations and shipped in cylinders. Each cylinder held about 191 cubic feet of gas under a pressure of 2,000 pounds per square inch at 68° F. temperature. When the war ended we had placed orders for 172,800 of these cylinders, of which 89,225 had been delivered and were in use. We developed a manifold filler which would take the gas from 12 to 24 cylinders at the same time and quickly inflate a kite balloon, a speed of 23 minutes for a complete inflation having been reported from one training camp.

In the production of portable hydrogen generators we had to produce not only the machine but the chemicals required in the process. We adopted the ferrosilicon and caustic soda process by which it was possible to produce 10,000 cubic feet of hydrogen per hour in a field generator. There was plenty of caustic soda to be had, but high grade ferrosilicon, a production of large electrolytic furnaces, was scarce, because of its heavy consumption in the steel industry. We procured, however, 2,482 tons of it for our generators, of which over 2,360 tons were supplied by the Electro-Metallurgical Sales Corporation alone.

An interesting feature of the gas supply in the field was the use of "nurse balloons." The nurse balloon was simply a large rubberized-fabric bag with a capacity of 5,000 cubic feet of gas. It was used for storage of gas, and the observation balloons were fed from it. We have not received the exact figures of the quantity of gas used by the entire Balloon Service; but, as one item alone, private manufacturers previous to the signing of the armistice produced and delivered 17,634,353 cubic feet of hydrogen and were in position to meet practically any demand for the gas. This figure is only a small part of the total, since it does not include the hydrogen produced in the permanent Government stations or by the field generators.

Hydrogen itself, while the lightest of cheap gases, and therefore the one universally used in balloons, has the grave fault of being dangerous to the balloonist. When mixed with the air it is highly explosive, if touched off by a spark of fire or electricity. For years balloonists have dreamed of a gas light enough to have great lifting power, but which would not burn nor explode. There was such a gas known to chemistry, and this was helium, discovered first in spectroscope examinations of the corona of the sun, but later found by chemists to exist rather freely in the atmospheric envelope of the earth. Although one of every 100 parts of air is pure helium, it was not until comparatively recent years that this light nonexplosive gas was discovered in our atmosphere.

Now helium was rare and expensive, and until the United States entered the war no one had considered its production as a commercial possibility. Up to two years ago the total world production of helium since its discovery had not been more than 100 cubic feet in all, and the gas cost about $1,700 per cubic foot.

It had been discovered that certain natural gases issuing from the ground in the United States contained limited quantities of helium. The question was whether we could extract this helium in sufficient quantities to make its use practical. The Signal Corps, the Navy, and the Bureau of Mines combined in a cooperative plan to develop a practical helium production. By adopting a method of obtaining the helium from liquefied gas produced in the processes of the Linde Air Products Co. and the Air Reduction Co., and also by the Norton process, we attained astonishing success in this enterprise.

On the day the armistice was signed we had at the docks ready for loading on board ships 147,000 cubic feet of helium. At its prewar value this gas would have been worth about $250,000,000. On November 11, 1918, we were building plants which would produce helium at the rate of 50,000 cubic feet per day, and the cost of obtaining it had dropped from $1,700 per cubic foot to approximately 10 cents.

None of this gas was actually used in the war, but its production by our chemists was hailed as the greatest step ever taken in the development of ballooning. It now seems to have opened a new era in lighter-than-air navigation. In war helium will nullify the incendiary bullet which destroyed so many balloons and airships. In peace it brings the possibilities of new types of construction of dirigible airships, since its use eliminates entirely all of the frightful dangers from lightning, static electricity, or sparks and flames from gasoline engines or any other source.

The Army and Navy cooperated in the production of balloons. The Army furnished the balloon cloth to the Navy. Navy balloons had two automatic safety valves for the expanding gas, one on each side of the balloon a third of the way back from the nose and just above the equator; while the Army held to the French and British idea of a single valve in the nose itself. The Navy adopted a Caquot-type balloon which rides at an angle of about 25° to the horizontal and is somewhat smaller than the Army model. The Navy used these balloons as spotters for submarines and mines. They were towed on cables from the decks of war ships, and were connected with the ships by telephone.

The use of parachutes with balloons is a comparatively recent development, the man who first successfully descended to earth in a parachute being not only still active and enthusiastic over aerial development, but being in fact the chief inspector of all United States Army balloons and parachutes. This is Maj. Thomas S. Baldwin, known the world over as Capt. "Tom" Baldwin, hero of innumerable aerial exploits of all kinds under all conditions and in all parts of the world, and at present chief of the United States Army balloon inspection. The Yankee balloon observer in France went up to his observation post in the security of knowing that the equipment on which his life depended had been O. K.'d by men who knew the business from beginning to end.

The parachute as it is known at the county fair and the parachute used in the recent war were far apart in type, the latter embodying all the improvements that the world's aeronautical experts could add to it. The need for parachutes developed when hostile aviators began shooting down the sausages. At first the one-man parachute was used exclusively, the men in the basket leaping overboard the instant their balloon was fired over their heads. Any delay on their part would be fatal, since the entire bag would be consumed in 15 or 20 seconds and the observer would then be unable to leap out of the falling basket. When the individual parachutes were used, the maps and records in the balloon basket were usually lost.

To overcome these difficulties, the designers invented the basket parachute. This was considerably larger than the individual parachute, and to operate it the balloonists pulled a cord which cut the basket away from the balloon entirely. The spreading parachute overhead then floated the basket, with the men themselves and all else it contained, safely and quickly to the ground.

Although hundreds and even thousands of parachute jumps occurred during the war, there were few fatalities from this cause. During all the time our forces were at the front only one of our men was killed as the direct result of a parachute drop. In that particular instance the burning balloon fell on top of the open parachute, setting it on fire and allowing the observer to fall unprotected the rest of the distance to the ground. One of our observers was known to make four jumps from his balloon on the same busy day, and another leaped thrice in four hours. In the Argonne offensive 30 balloon jumps were made by our men.

As to the safety of our parachute equipment, the only complaint from the Yankee balloonists at the front was that they were too safe. The man who is escaping from a German airplane nose-diving at him with a machine gun spitting fire is in a hurry and does not wish to be detained by a parachute which floats him too slowly to the earth.

In the rigging of each kite balloon there are about 2,000 feet of rope of different sorts. There was a shortage of proper cordage in the United States at first, and the French thought they could furnish this rigging to us. But this attempt proved to be unsuccessful, and we were forced to develop a cordage manufacture in this country of high quality and great quantity. We did this so swiftly that there was no serious delay to the balloon production.

Up to November 11, 1918, we produced over 1,000 balloons of all kinds, 642 of these being of the final Caquot type which we adopted. This production included many propaganda balloons for carrying printed matter over the lines into the enemy's country. We supplied several target balloons for gun practice on our aviation fields. We developed new types of parachutes and built acres of canvas hangars for balloons. We produced 1,221,582 feet of steel mooring cable. These are only the major items in the balloon enterprise, and do not include hundreds of others of less importance.

The balloon production was one of the most important and successful of all our war projects. Although we had a limited knowledge of the subject in the beginning, our balloons stood the hard test of actual service and could bear comparison in every way with the best balloons of Europe, where the art of balloon building had been in existence for many years. Once our production actually started, we never had any shortage of balloons for our own Army; and soon we would have been in a position to produce the observation balloons for all of the armies fighting Germany, if called upon to do so.

Balloon production figures.

BALLOONS AND PARACHUTES.

----------------+--------------+--------------+---------------+------------ | Observation | Supply | Miscellaneous | Parachutes | balloons | balloons | balloons |produced to-- |produced to-- |produced to-- | produced to-- | Firm. +--------------+--------------+---------------+-------+----- |Nov.11,|Mar.1,|Nov.11,|Mar.1,|Nov.11,|Mar.1, |Nov.11,|Mar.1, | 1918. |1919. | 1918. |1919. | 1918. |1919. | 1918. |1919. ----------------+-------+------+-------+------+-------+-------+-------+----- Goodyear Tire & | | | | | {[30]3| [30]3 |} | Rubber Co., | 458 | 565 | 39 | 39| {[31]5| [31]7 |} 20 | 20 Akron, Ohio | | | | |{[32]53|[32]53 |} | | | | | | | | | B. F. Goodrich | | | | | | | | Rubber Co., | | | | | {[30]3| [30]3 |} | Akron, Ohio | 169 | 279 | 10 | 10 | {[31]1| [31]1 |} 15 | 15 | | | | | | | | Connecticut | | | | | | | | Aircraft | | | | | | | | Corporation, | | | | | | | | New Haven, Conn.| 22 | 37 | 72 | 72 | [31]1| [31]3 | | | | | | | | | | United States | | | | | | | | Rubber Co., | | | | | | | | East Cambridge, | | | | | | | | Mass. | 23 | 37 | | | | | | | | | | | | | | Knabenshue Manu-| | | | | | | | facturing Co., | | | | | | | | East Northport, | | | | | | | | Long Island | 3 | 25 | 1 | 1 | [31]1 | [31]1 | | | | | | | | | | French-American | | | | | | | | Balloon Co., | | | | | | | | St. Louis, Mo. | 1 | 1 | | | [31]2 | [31]2 | | | | | | | | | | Scott-Omaha Tent| | | | | | | | & Awning Co., | | | | | | | | Omaha, Nebr. | | | | |[32]161|[32]161| 53 | 228 | | | | | | | | New York Tent & | | | | | | | | Awning | | | | | | | | Co., New York | | | | | | | 63 | | | | | | | | | Follemer-Clogg &| | | | | | | | Co., Lancaster, | | | | | | | | Pa. | | | | | | | 104 | 131 | | | | | | | | Bickford Bros., | | | | | | | | Rochester, N. Y.| | | | | | | 1 | 1 | | | | | | | | Firestone Tire | | | | | | | | & Rubber Co., | | | | | | | | Akron, Ohio | | | 7 | 7 | | | | | | | | | | | | Columbia Mills | | | | | | | | (Inc.), | | | | | | | | Wilkes-Barre,Pa.| | | | | [32]1| [32]1 | | --------+------+-------+------+-------+-------+-------+----- | | | | | {[30]6| [30]6 |} | Total | 676 | 944 | 129 | 129 |{[31]10| [31]14|} 256 | 458 manufactured | | | | |{[32]215|[32]215|} | | | | | | | | | Total shipped | | | | | | | | to ports | 481 | | 6 | | | | 4 | | | | | | | | | Total shipped | | | | | | {[30]6|} | to camps, etc. | | 463 | | 123 | |{[31]14|} |418 | | | | | |{[32]215|} | ----------------+-------+------+-------+------+-------+-------+-------+-----

[30] Target.

[31] Spherical.

[32] Propaganda.

WINDLASSES.

------------------------------------------------+--------------+------------- | Produced to-- Firm. +--------------+------------- |Nov. 11, 1918.| Mar. 1, | | 1919. ------------------------------------------------+--------------+------------- McKeen Motor Car Co., Omaha, Nebr. | 23 | 35 Chris D. Schramm & Son, Philadelphia, Pa. | 20 | 20 Jas. Cunningham & Sons Co., Rochester, N. Y. | 5 | 35 N. C. L. Engineering Corporation, Providence, R.| 1 | 37 I. | | Deloies Hoisting Co., New York | 1 | 1 +--------------+------------- Total manufactured | 50 | 128 Total shipped to camps and depots | | 124 Total shipped to ports | | ------------------------------------------------+--------------+------------- CABLE. ------------------------------------------------+--------------+------------- | Feet. | Feet. John A. Roeblings Sons Co., Trenton, N. J. | 476,700 | 860,700 American Steel & Wire Co., Worcester, Mass. | 744,882 | ------------------------------------------------+--------------+------------- Total manufactured | 1,221,582 | 860,700 Total shipped to ports | 486,000 | Total shipped to camps and depots | | 1,119,582 ------------------------------------------------+--------------+------------- HYDROGEN GAS. ------------------------------------------------+--------------+------------- |Cubic feet. |Cubic feet. | | Oxygen Gas Co., Kansas City, Mo. | 2,715,845 | 3,568,600 Southern Oxygen Co., South Washington, Va. | 945,412 | 1,608,778 International Oxygen Co., New York | 2,166,668 | 2,166,668 Walker Refining Co., Austin, Tex. | 496,000 | 595,783 Tarrifville Oxygen & Chemical Co., | | Tarrifville, Con. | 1,072,590 | 1,072,590 Louisiana Oxygen Co., New Orleans | 477,500 | 904,576 Kentucky Oxygen Co., Louisville, Ky. | 276,779 | 540,752 Burdett Oxygen Co., Chicago | 9,532,559 | 11,347,999 +--------------+------------- Total produced | 17,683,353 | 21,805,746 Total shipped overseas | 7,349,578 | Total shipped to camps | | 14,456,168 ------------------------------------------------+--------------+------------- HYDROGEN CYLINDERS. ------------------------------------------------+--------------+------------- National Tube Co., McKeesport, Pa. | 35,800 | 43,300 Harrisburg Pipe & Pipe Bending Co., | | Harrisburg, Pa. | 38,425 | 65,500 Tindel-Morris Co., North Eddystone, Pa. | 15,000 | 15,000 +--------------+------------- Total manufactured | 80,225 | 123,800 Total to ports | 30,000 | Total to camps and warehouses | | 95,800 ------------------------------------------------+--------------+-------------

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I. THE ENGINEERS IN FRANCE

In describing the activities of the Engineers, we are carried to the front itself, into the zone beaten by enemy fire, where machine-gun bullet, bursting shell, and deadly gases have brought sudden death and painful wounds to many members of the technical services. A large proportion of the Engineers are combatant troops, constituting in the American Expeditionary Forces about 8 per cent of the total combatant troops engaged. These troops, trained and equipped to march and fight as Infantry, demonstrated their fighting qualities during the war on numerous occasions, both when used as Infantry to increase the rifle strength of that arm and when fighting as Engineers to obtain possession of terrain as a preliminary to the exercise of their technical art in its organization.

From the day the first sector was taken over by American troops in November, 1917, until the Meuse River was passed and the enemy, in flight, sought an armistice to save his armies from destruction, the combatant Engineers--the "sappeurs" of French soldier lore and song--- fought and bled in a manner never to be forgotten. Railroad engineers, nominally considered noncombatant, at Cambrai dropped their tools to take arms and stand stubbornly shoulder to shoulder with their British brothers with whom they were learning to work under the special conditions of the front. From Cantigny to Chateau Thierry, Engineer troops fought as well as worked, and often not only advanced with the Infantry under or through the barrage, but actually led the first wave, to demolish or remove the obstacles placed in its path. Through the days when from March 21, 1918, until July 18, 1918, the German army made its rapid plunges toward Paris until checked and thrown back across the Marne at Chateau Thierry, the sapper troops fought and worked with the Infantry of their divisions, enduring the same dangers, privations, and hardships, and winning equal honors and commendation.

In the drive at St. Mihiel and through the Argonne, the combatant Engineers played a conspicuous part. Advancing with the tanks, they made possible the passage of many difficult points for these lumbering monsters, against which was directed a particularly destructive fire. Using elongated torpedoes of high explosive, known as Bangalore torpedoes, they prepared passages for the Infantry through the broad barbed-wire entanglements, echeloned in depth by numerous separate lines, each to be breached and passed before the objective could be gained. In this work the Engineers reduced the machine-gun nests that hindered their operation, cleaned up the strong points that delayed the advance of the tanks they were assisting, and threw extemporized footbridges across the streams which barred the further advance of the Infantry.

The combatant Engineers did their part in the winning of the reconquered ground as well as the lion's share of its organization for the defense and the maintenance of the communications behind it. In this last respect alone, the Engineers, as combatant troops, opened across No Man's Land the first communications practicable for the light field artillery, which pressed forward immediately behind the Infantry troops to their support and protection.

Filling in trenches, removing wire entanglements, building trestles across wide mine craters, searching for and rendering inoperative treacherous mines and traps of extreme ingenuity and destructiveness, the sapper found a wide field for the exercise of his functions. Shattered and obliterated by four years of shelling and mining, trenching, and countermining, the "roads" across No Man's Land existed only on the map; and as they retreated the Germans demolished and obstructed the highways behind the old front from which they had been driven, with the thoroughness and attention to detail for which they are noted. As our Infantry advanced, upon their heels, literally speaking, came our Engineers, to attack the problem of providing for the Artillery and supply trains a means of following. From the standpoint of the road builder in civil life, their methods were crude in the extreme, but for the military purpose and the pressing immediate needs, their road building achievement was adequate. The Engineers sometimes reopened abandoned quarries, and sometimes started them where none had existed before, to obtain a supply of road metal, which supply was sometimes supplemented and in some cases replaced by the use of debris from ruined villages and shattered farmhouses. From demolished structures many useful materials were extracted and adapted to the military purpose by the Engineers. Where bridge and trestle timbers were lacking, deserted buildings--in one case the tower of a ruined church--filled the need. Where shell hole or crater yawned a remnant of a stable wall might be pulled down by ropes and man power, and broken up to fill the void.

Through the dense woods the soft forest floor offered no support even to the light artillery, and miles of corduroy and brush path were built to permit the guns to advance to the reinforcement of the attack. In many places the tactical situation admitted of insufficient time to build even the crudest paths, and then the Engineers fell to and assisted artillery and supply wagons to get through and over the bad spots, replacing guns on the road where they had run into the ditch, righting and reloading combat wagons when they had turned over in shell holes or deep ruts.

While thus engaged the sapper troops were subjected to the fire of enemy artillery seeking to prevent the advance of the supporting guns, and, further, they were working within the zone of combat of enemy aviators, the rattle of whose deadly machine guns, as they plunged at low altitude toward a busy working party, was as much to be dreaded as the high-explosive bombs which they dropped.

Behind the combatant Engineer troops, extending through the service of supply to the base ports and across the ocean to the United States was an organization of technical noncombatant supply and administration.

The work of these production, construction, and supply departments of the Engineer service in France was organized in the American Expeditionary Forces under the administration of three divisions of the office of the Chief Engineer. These were the division of military engineering and engineering supplies, the division of construction and forestry, and the division of light railways and roads.

ENGINEERING SUPPLIES.

The division of military engineering and engineering supplies was charged with the procurement, standardization, and distribution of all classes of supplies used by Engineer troops. During the 19 months of warfare this division handled 3,225,121 tons of supplies, storing them and distributing them from immense depots aggregating 25 acres of covered storage and over 756 acres of open storage. This service was further charged with the current investigations into new developments of the art of military engineering, and with the development, operation, and administration of certain technical branches of the American Expeditionary Forces, such as electrical and mechanical troops, water-supply troops, searchlight regiments, etc.

At its seven storage depots in the base, intermediate, and advance sections, this division had in service 23 locomotive cranes, mostly of 15 tons capacity and capable of handling an enormous amount of freight and material at warehouses and cars. The following table of principal items of engineer material shows the kinds and quantities of supplies which were received in France for issue through this division up to December 15, 1918:

Table of engineer supplies received in France.

To facilitate the procurement of supplies in the existing world markets, this division established in Paris a purchasing board, having branches in England, Switzerland, and Spain. When the war ended this board had accomplished the tremendous task of buying over 1,800,000 tons of engineer supplies, with a total value of $205,242,728. In addition to this material, our own country furnished over 1,500,000 tons, with a value of $248,993,322. France sold to us through this board 1,234,968 tons, valued at $134,393,870, and England 396,000 tons, valued at $56,145,818. In Switzerland, purchases consisting principally of sectional barracks and technical equipment, totaled 96,867 tons, with a value of $14,643,410. Purchases from Spain amounted to only 797 tons, with a value of $59,630.

Much work was done in standardizing supplies of all classes, so that quantity-production methods could be used in their fabrication, thus promoting economy and stimulating the rapidity of supply.

In the procurement of cement for the use of the American Expeditionary Forces, the Engineers dealt successfully with a problem of large magnitude and importance. By contract with English and French mills, by direct purchase for specific jobs from local mills, and by their own manufacturing operations, the Engineers secured enough cement to supply the demands for construction both at the front and in the S. O. S., as the service of supply was generally known. Three large cement mills were leased from the French owners and operated by special troops organized in the United States. To certain other French mills the Engineers furnished labor and materials in return for a certain proportion of their output. It is estimated that about 215,000 tons of cement were thus procured, representing a total cost of about $7,000,000.

The Engineers operated shops at various points near the front in which were manufactured standard material for dugout, trench, and emplacement construction, such as concrete beams, concrete slabs for overhead protection against high-angle shell fire, trench frames, revetment material, trench duck boards, mine and gallery timbers, knockdown bunk sets, etc.

CONSTRUCTION AND FORESTRY.

The division of construction and forestry was charged with all construction work in the service of supply, and also with the procuring of forest products for the American Expeditionary Forces. At the signing of the armistice its organization totaled 150,823 men, of whom about 127,000 were constantly engaged in production work. Using standardized building plans, this force performed a huge amount of construction work in France.

It was assumed that one-third of the American troops in France would have to be housed in new buildings erected specially for the purpose. Thus accommodations for about 750,000 men had to be built at the rate of 16 barracks, each 20 by 100 feet in size, for every 1,000 men. Contracts were let to British and French contractors for 23,000 demountable barracks, this order being based on the ultimate probable size of the Expeditionary Forces. During August, September, and October, 1918, these barracks were being received at the rate of 1,000 per month. To supplement a supply of even such magnitude, our own type of barrack was developed to be built with lumber furnished by the American forestry forces in France. One cantonment project involved the construction of 500 barracks, accommodating 55,000 men. A total of 11,862 barracks were erected for the American Expeditionary Forces in France, representing 225 miles of length, if all the barracks were placed singly end to end.

It was the policy of the American Expeditionary Forces to provide hospital room sufficient to give beds, if necessary, to 15 of every 100 American soldiers in France. On this basis the Engineers set out to provide hospitals with a total of 280,000 beds. Of these, 139,000 beds were in hospitals taken over from the French, 25,000 beds being added to this capacity by new construction. In entirely new base, camp, evacuation, and convalescent hospitals, 116,000 beds were ultimately made available for the casualties of the American Expeditionary Forces, requiring the erection of 7,700 hospital barracks of special type, all of which would have totaled 127 miles in length if placed singly end to end. As to the progress of this construction, on November 14, 1918, there were 190,356 beds occupied in American hospitals in France, but all 280,000 beds originally specified were ready and available.

The base hospital plants were complete municipalities in themselves, and had capacities varying from 1,000 to 6,000 beds. These units were built where nothing had existed before but little French rural communities, devoid of the improvements and modern conveniences with which we in this country are so familiar. To establish a modern military hospital, capable of caring for the varied casualties and illness arising from action and abnormal living conditions, it required the construction of roads, sidings, unloading platforms, sorting and classification buildings, operating rooms, surgical and medical wards, dormitories, morgues, cemeteries, complete water supplies, fire protection systems, sewage and garbage disposal plants, recreation buildings, electric light plants, and all that goes to make complete a modern installation for the care of the wounded and sick. Many of the camp and evacuation hospitals required construction of the same character, but differing in magnitude.

The Engineers developed port faculties at St. Nazaire, Bordeaux, La Pallice, Marseilles, Brest, and at less important harbors. In general, at these places the existing facilities were expanded to meet the needs for the debarkation of troops and the unloading and shipment of supplies. Originally 23 ship berths were placed at our disposal by the French. The Engineers expanded this equipment to a total of 89 berths, with authorized projects for 160 berths by June, 1919. Our overseas shipments grew from 20,000 tons in July, 1917, to 1,000,000 tons in October, 1918, but the port expansion kept abreast of this development. Fifty-eight 300-ton lighters were built by Engineer troops with French timber, and twenty-six 500-ton lighters with American timber. The Engineers constructed seven derrick barges with lifting capacities ranging from 30 to 100 tons.

The existing French railroads running from the base ports to the advanced zone were quite inadequate, so that it was necessary to supplement their facilities with many miles of new track and other construction, including important storage, classification, arrival, and departure yards, warehouse tracks, engine terminals, water points, and repair shops. At Bassens, St. Sulpice, Miramas, and Montoir, enormous storage depots were constructed to handle the supplies entering France for our forces. The American-built railroad yards at these points were comparable in magnitude and completeness to the important yard developments undertaken in this country in recent years by the large railroad systems, the yards at St. Sulpice having a trackage totaling 147 miles of single track. Those at Bassens and St. Sulpice were virtually completed during the war, while the construction at Miramas was well under way at the signing of the armistice. At St. Sulpice the project was designed on the basis of receiving, storing, and forwarding the supplies for 1,000,000 men for 30 days. The others were of like magnitude.

At Nevers, in the intermediate section, a condition existed requiring the construction of six miles of new double-track line, with a bridge over the Loire River 2,190 feet long. This piece of construction is known as the "Nevers Cut Off." It relieved the railroad congestion at this important point.

At Is-sur-Tille, in the advance section, was built a regulating station at which train loads of supplies and troops were dispatched to points where needed. Still farther toward the front, at Liffol-le-Grand, was another and smaller regulating station, controlling troop movements and the distribution of munitions and subsistence. Both of these projects were entirely new and were in useful operation when the war terminated.

In addition to the above projects, many storage yards, hospital tracks, ordnance depot yards, aviation center tracks, and construction tracks were laid out and built. In all 937 miles of single track were laid, thus fulfilling in the equivalent the prediction that to supply an American Army at the front we should have to build a double-track railroad from the French coast to the trenches.

Storage depots, remount depots, and veterinary hospitals erected by the Engineers proved entirely adequate for the needs of the American Expeditionary Forces at all times. A grand total of 536 acres of covered storage was built or acquired, of which about 482 acres was new construction. Space was provided in remount depots for 29,000 animals, and it was projected to accommodate 48,700 animals had it been necessary. Veterinary hospital space was provided for 17,250 sick animals. Each veterinary hospital required much special construction, such as concrete dipping tanks for the treatment of mange, operating rooms, exercising paddocks, hay sheds, living quarters for attendants and veterinary surgeons, and administration buildings.

At Gievres, in connection with the important storage depot built there, was constructed the third largest refrigerating plant in the world. This plant, built by the Engineers from plans prepared by experts, was capable of caring for 5,200 tons of meat at once, and of producing 250 tons of ice per day. Another similar plant at Bassens had a capacity for 4,000 tons of meat.

Miscellaneous construction work in France covered many fields of activity. The question of adequate water supply was ever present, and in most places where hospitals, depots, shops, or warehousing plants were built, a water supply development was incidentally necessary. Many systems were installed complete from the collection of the water at its source to its distribution to the points of consumption, while in some other cases only extensions and ameliorations of existing systems were undertaken. Water supply in the service of supply was placed under as fine and complete a system of bacteriological inspection and examination as is customary under more normal conditions. At Tours, Vierzon, St. Nazaire, and Dijon, where unfavorable bacteriological conditions existed, arrangements were entered into with these municipalities whereby the existing water supplies were chlorinated by the American water supply service.

At Is-sur-Tille was built a mechanical bakery at which 500,000 pounds of bread, fresh for immediate shipment to the troops at the front, could be produced in one day. Another such plant was built and put into service at Neufchateau, and at Liffol-le-Grand it was proposed, and plans had been prepared, to construct a third plant for 400,000 pounds of bread per day, but this project was canceled just after the armistice. In addition to these plants, bakery capacity for 240,000 pounds per day was provided at the base ports.

Oil storage was provided for 175,000 barrels of oil and gasoline. The large plants, with tanks having a capacity of 25,000 barrels each, built with enduring concrete foundations and equipped with connections and pumping plant for the loading of tank cars destined for the front, rivaled in size the installations at large refineries of this country.

For the operation of these many plants numerous power developments were undertaken, and a total of 5,000 kilowatts of new power, being provided for at the time of the armistice, was canceled. Plants of the capacity of 750 kilowatts each, providing 3,500 kilowatts of electric power in all, were in operation when the armistice was signed, not to mention numerous smaller units installed at various points where needed.

Ordnance repair shops were erected, as were also assembling plants for ordnance material, and heavy gun-mounting plants. Repair shops of enormous extent were established near the front, equipped with machine-tool equipment for the repair and maintenance of tank and motor transport material. Schools for the line and staff were constructed, the first and largest being at Gondrecourt and Longres. Laundry plants, salvage depots, aviation assembly plants, sewage disposal plants, refuse incinerators, mechanical repair shops, locomotive assembly plants and locomotive round-houses were placed at convenient points. At Chalmdray and at Colombey-les-Belles, both within a short day's automobile ride of the front, were the tank and air-service repair depots, each one covering many acres of ground and each provided with full equipment for any job of manufacture or repair in their respective fields.

The forestry work of the American Expeditionary Forces was developed to meet the heavy demands of our armies for forest products of all kinds. The first move in this direction was the dispatch to France of the Tenth Engineers, a forestry regiment of two battalions. This was in September, 1917. By the spring of 1918 we had recruited and trained the Twentieth Engineers, a forestry regiment of 10 battalions. Later additional forestry troops were sent across. Shortly before hostilities ceased all these troops were consolidated into a single regiment of 13,000 men, known as the Twentieth Engineers. To this force were added negro service troops to the number of 9,000, making 22,000 men engaged exclusively in the work of cutting down French forests and turning them into lumber required by our forces.

At first we had difficulty in supplying the necessary machinery. Until the sawmills came the forestry troops were engaged in building camps and hewing out railroad ties. In January, 1918, the machine equipment began to arrive. In February our troops cut about 3,500,000 feet of lumber; while in October the cut for the single month had reached the enormous figure of 50,000,000 feet. When the war ended we were expanding our forestry operations in France to produce 1,000,000,000 feet of lumber in a year.

The lumber produced by our sawmills in France up to November 30, 1918, would build completely enough barrack buildings 20 feet wide to stretch out to a distance of 600 miles if placed end to end, quarters enough for 3,107,600 men. In addition to this output the railroad ties produced would build 1,091 miles of standard-gauge railway and the small ties for the 24-inch track would build a double-track railroad behind 185 miles of trenches.

Just the posts and poles produced, if all cut into 6-foot posts, would be sufficient to support a wire fence, with posts one rod apart, reaching one-third of the distance around the earth. The piling, if stood end to end, would make a flagpole 362 miles high. The cord-wood produced would make a rack 1 yard wide, 1 yard high, and 600 miles long.

The sawmill machinery installed to accomplish such a production comprised 30 mills of 20,000 feet per day capacity, 56 mills of 10,000 feet per day capacity, and 92 smaller mills capable of producing ties and rough timber.

In the base and intermediate sections a large amount of work was necessary in the maintenance of the existing roads and highways, and in the construction of new roads in the vicinity of the various new projects. Experienced road engineers, drawn from civil life and commissioned as officers of the Army, were put in charge of this work, and specialist engineer troops and labor battalions were assigned to them. Quarrying the rock, grading the road, surfacing it, and maintaining it in good condition thereafter--all these duties fell within the province of the engineers.

LIGHT RAILWAYS AND ROADS.

The light railway and road regiments of engineers attached to the armies at the front, while their duties did not carry them so far or so much into the zone of enemy fire, may be considered as combatant units, since they operated with and in support of combatant troops in the field. To the light railway regiments were assigned the construction, operation, and maintenance of the light railroads of 60-centimeter gauge (about 24-inch gauge). A great quantity of such trackage was used during the war. These narrow-gauge railroads, capable of being operated under extreme conditions of grade and curvature, and powered with light steam and gasoline locomotives, were essential to the proper supply of a stabilized sector. They were the lines of communication between the railheads of the broad-gauge system and the dumps and depots within the front sectors. At the very front, sometimes within a few hundred meters of the German lines, these light railroads were operated by hand or animal traction, while further back the gasoline locomotive, less conspicuous than the steam engine, came well within range of the enemy's light field pieces. In periods of activity and during an advance these railroads did a tremendous service, not only in transporting troops, munitions, materials, and subsistence stores, but in affording a means of bringing up rapidly a certain class of railway artillery adapted for use upon 60-centimeter gauge trucks. Built of light rail and steel ties assembled in portable sections, this track was easily destroyed by shell fire, and such was often its fate, yet it was but short work for the engineers to replace broken sections with new material, a work frequently done under heavy fire. Engineer troops suffered many casualties in this service.

In cooperation with the Engineer Department in the United States, a practical, efficient, and standard type of narrow-gauge motive power and rolling stock was developed by American manufacturers. This material was shipped to France knocked down, and was assembled and set upon the rails at Gondrecourt, where a plant for this purpose had been established. Up to November 30, 1918, there had been built and placed in operation 538 miles of 60-centimeter track, with 347 steam and gasoline locomotives furnishing motive power for the operation of 3,281 cars of different types.

The road-building regiments in the zone of the armies built and maintained the roads immediately behind the front. Equipped with modern road-building machinery and motor trucks, these regiments maintained the roads in shape to handle the abnormally dense and heavy traffic incidental to operations at the front. The Army road troops were recruited from among men accustomed in civil life to road building, quarrying, and construction operations. They usually worked well within sound of the enemy guns, and frequently under their direct fire. During the advances made from the stabilized line of June, 1918, these regiments improved and perfected the hasty roads thrown across No Man's Land by the sapper regiments of the fighting divisions, so that transport of supplies and troops could be maintained to the advancing armies. To furnish materials for this construction many quarries were opened or taken over from the French road service. A total of 42,000 cubic meters of rock was quarried and prepared for use in quarries operated exclusively by American engineers, while in quarries jointly operated with French forces 75,000 cubic meters were produced.

MAP MAKING AND PRINTING.

A vitally important part of the work of Engineer troops was the making and reproduction of the many maps required for the conduct of tactical and strategic operations by the American Expeditionary Forces. A highly specialized regiment was organized to conduct the topographic surveying operations, map reproduction, and printing work in France. Many of the officers of this regiment had been formerly connected with the American Coast and Geodetic Survey and the Geological Survey, and they were well qualified for the work of war-map making. At Chateau Thierry a portion of this organization rapidly mapped to a large scale the new region in which the theater of operations suddenly found itself, thus supplementing the excellent small-scale map which was in existence for the whole of France, but which was not sufficiently precise for the conduct of our artillery fire. This work was done under pressure, but it contributed its share to the later American successes in that locality. These troops also were charged with furnishing to the Artillery the mathematical azimuths and coordinates, on the basis of which artillery indirect fire was executed.

The maps in use even on stabilized fronts were in a constant process of revision and change. The data and information on which these changes and revisions were based were constantly pouring in from the photographic branch of the air service, from the intelligence service, the Artillery, and from the sapper regiments at the front. Consequently new maps had to be prepared continually and furnished to all the organizations and officers concerned with their use. Then, too, an Army as large as ours required an impressive amount of field printing in order to distribute its orders and information.

As soon as our forces reached France it was apparent that the French map-production plant could not take care of our needs. The Chief of Engineers in the United States thereupon ordered the purchase of equipment for a base printing plant large enough to take care of all the map printing for an army of 1,000,000 men. The special machinery ordered in the United States for this plant did not arrive in France during 1917, and so the American Expeditionary Forces purchased abroad five large rotary lithographic presses, several type presses, and a number of linotype machines and other printing equipment.

The base printing plant was established at Langres, France. In the spring of 1918 the American equipment arrived, and thereafter the base printing plant was able to print not only the current maps required but also the base maps which the French had been supplying. In addition, during the heavy fighting in July and August, 1918, our printing plant supplied to the Seventh and Eighth French Armies the base maps of their fronts.

The demands for maps and printing steadily increased until the base printing plant grew to have a working force of 35 officers and 750 men. From July 15 until September 15, 1918, the plant worked continuously 24 hours a day to turn out the work required. By this time the shop had 10 rotary lithographic presses, 4 linotype machines, and several job presses, printing each month an average of over 1,200,000 lithographic impressions and 500,000 sheets of printed matter. In November the plant turned out 1,900,000 lithographic impressions and over 1,000,000 sheets of type work.

To supplement the base printing plant we had at each army headquarters an advanced printing shop to supply maps when they were needed within a few hours. At the base printing plant we had a department for making relief maps, which work had been done for us previously by the French Government.

The equipment for military map making was enriched during this period by an invention of Maj. James N. Bagley, United States Engineers, called the aerial cartograph, or map camera. The Bagley camera's three lenses at the height of 5,000 feet could photograph a strip of territory 3½ miles wide.

MILITARY BRIDGES.

The science of building military bridges is an old one. When war with Germany was declared the United States had developed its heavy ponton equipment, which was standard in design and yet which had changed but little since the Civil War. As soon as we formally took the step to send troops against Germany the Engineers ordered great quantities of this equipment and by the latter part of 1917 had plenty of it ready to go overseas. Our deliveries to France, however, were hindered by the shortage in ocean tonnage, particularly after we had begun to use every available ship for the transport of men.

Meanwhile the efforts of the Engineers were being directed to the development of standard ponton equipment strong enough to carry tanks and the ponderous artillery of the present day. The old ponton bridge was first strengthened to carry loads of 5 tons on each of two axles spaced 10 feet or more apart. The standard prewar equipment would support only 3 tons similarly spaced.

The next step was to develop a bridge that would hold up axle loads of 10 tons with a distance of 12 feet or more between axles, although in actual use this bridge showed itself capable of supporting a load of 15 tons concentrated on one axle. As soon as these developments were made, the plans were mailed to the American Expeditionary Forces, so that the Engineer Corps abroad could provide the beams and metal parts at its own mills and shops in France. When the fighting ceased, the Engineers were designing a raft capable of transporting the heaviest portable ordnance then under manufacture in the United States.

In 1917 the Engineer Department made designs for a standard sectional steel bridge, consisting of short latticed steel truss sections capable of being assembled to form trusses varying by increments of 11 feet up to a maximum span of about 90 feet. Two of these trusses with the span mentioned were capable of supporting a load of 30 tons, and they could be erected in a matter of hours over abutments prepared in advance or extemporized from the ruins of a demolished structure. These bridges had been manufactured in quantity in this country and were ready for shipment when the armistice was signed.

In the Argonne push Army bridge troops repaired and replaced the bridges destroyed by the retreating enemy as fast as material and labor could be provided at the points needed. For this work much heavy timber was utilized, and, in general, trestle structures were erected as best meeting the conditions of relatively soft crossings and soft river bottoms.

The fighting in the French terrain with its numerous narrow but deep streams and canals indicated to us the desirability of a portable floating footbridge. Such a bridge was designed and produced by the Engineers in France. Many of the crossings of the Meuse River and near-by canals under machine-gun and artillery fire from the high hills on the eastern side were made possible by the use of these bridges.

CAMOUFLAGE.

While camouflage has existed in nature since the beginning of time, its application to warfare on a grand, scientific scale was almost solely a development of the great war. Camouflage, due to the great developments of aerial observation and aerophotography, as well as of air bombing and indirect artillery fire, became a vital necessity for every branch of the service, far back in the rear as well as at the front. Any matériel or personnel the position of which was observed was at the mercy of the enemy, but, further, such observation might betray strategic plans. The need for camouflage became universal.

Camouflage organization was carefully developed for both the field and the factory, while one of the most important duties, that of instruction, was carried out in Army and corps schools and artillery camps, where thousands of officers and men were taught both the necessity and the methods of camouflage.

Our undertakings in this direction were based largely upon the methods developed by the French and British. In one respect camouflage was a matter of quantity production. This was in the manufacture of material used for concealing guns, roads, and other strategic locations which fall under the eyes of enemy observers on the ground or in the air.

In this work the British did nothing without the most careful scientific investigation, including the aerial photography of all their materials used, while the French relied more on their innate artistic sense of color and form. The camouflage material produced in quantity by the British consisted principally of burlap cut in strips about 1 inch wide and 12 inches long, colored in the desired hues with oil-emulsion paint. For artillery cover this was knotted in fish nets and chicken wire. The French for this purpose used raffia, a common product of Madagascar, whose natives use it largely for making their fantastic garments. The raffia was dyed and then knotted on nets and wire in the French camouflage factories.

After a careful study we adopted the British system and used burlap. Our Engineers made this decision because of the impossibility of finding permanent dyes for raffia and because raffia is more inflammable than burlap and scarcer and higher in price.

The first demand for camouflage material which we received embraced coverings for guns, sniper's suits, dummy heads, silhouettes, and some airplane hangar covers. In order to supply this material at the outset the engineering forces abroad leased a factory building in Paris and turned out a sufficient quantity with a working force of 30 enlisted soldiers and 100 French women.

But, as the American troops at the front increased in number, the demands for camouflage material became rapidly heavier. Battery positions of some types required about 4,000 square yards of camouflage cover. Aviation hangar covers were demanded in large numbers, and each one was a special order due to the varying conditions of terrain encountered. It became evident that we needed a vast increase in our camouflage-factory space.

In January, 1918, the Engineers secured about 20 acres of ground in Dijon, Haute Marne, a city on the main supply line north through the regulating station at Is-sur-Tille. They started to erect buildings immediately, and within 20 days this plant began turning out material. By November the Dijon factory numbered about 40 buildings, including blacksmith and machine shop, a sewing shop, a paint shop, laboratory, and a toy shop where dummies and silhouettes were made. The factory turned out artillery cover at the rate of 50,000 square yards per day.

The total output of camouflage cover for all purposes required about 3,000,000 square yards of burlap per month. When the fighting stopped the American Expeditionary Forces were using camouflage materials to the value of $1,500,000 monthly.

By new methods of manufacture, we succeeded in reducing the weight of fish-net covers. We designed two important field devices, one being an improved frame and set for mobile artillery protection, this equipment being later adopted by the British, and the other an umbrella machine-gun cover having special advantages. The central camouflage works of the American Expeditionary Forces at Dijon was declared by unprejudiced observers to be the best equipped and most efficient of any on the western front.

When the Dijon camouflage plant was projected it was expected that the American forces would require great quantities of camouflaged observation posts, silhouettes, dummy heads, snipers' suits, and other concealing devices. It was for this production that the toy shop at Dijon was erected, this shop being a kind of studio for the painters and sculptors connected with the Fortieth Engineers, which was the camouflage regiment. These various devices for deceiving the enemy, however, were used principally in the stagnant action of the trench warfare deadlock. By the time American forces came into the war in large numbers the struggle had become one of movement in which the trenches were left far behind. Also, American troops found themselves largely in sectors which were well wooded and therefore provided plenty of secure observation. The result was that there was never a great use on the part of American troops of these clever and interesting exploits in camouflage with which the public is familiar.

One of the best observation posts was the imitation of a tree trunk made of armor plate and set up in advanced positions during the night. Both the British and the French made considerable use of these. The British tree consisted of an oval shell of manganese steel. This was covered with tin, crimped in imitation of bark, and further camouflaged with paint and plaster and natural bark.

When it was desired to set up such a post a camouflage artist would surreptitiously make a faithful sketch of the tree trunk to be duplicated in armor plate. This sketch was then taken back to the workshop, where the spurious tree was built in exact duplication. The metal tree was built to rest on a base with hinges holding it down on one side. During the night two saps, or trenches, would be dug to the natural tree selected. Workers in one of these trenches would fell the branchless stub and carry it back out of the way. The armor plate tree would be drawn up in the other trench. The base would be set in place, and then the whole tree was raised on its hinges by means of ropes until it was upright and as life-like as artistry could make it. Inside the tree was a flight of iron steps leading to a seat in the upper part of the trunk. At this seat were peepholes and a stand for the phone which was connected up with the exchange at the adjoining trench. The sap, covered over, served as the gallery leading back to the trench.

The American camouflage force built only a single one of these trees, using it as a training device. Such objects were useless in an advancing movement, since, under such circumstances, they would play an important part only a short while and would then be left far in the rear.

The Dijon factory, however, turned out a number of small observation posts for use at the edges of shell holes. These were known to our troops as beehives and to the English soldiers as domes. Each one was built of light metal and covered with chicken wire and plaster. It was camouflaged with paint and bits of grass to simulate the appearance of the surrounding terrain, often being studded with tin cans or old shoes to make it appear to be an accumulation of rubbish. The favorite way of making the peephole for a beehive was to cover with gauze a hole cut in the bottom of an old shoe, which was then fastened to the observation post.

Another device built by the Dijon factory was the trench periscope. This was built and set up to look like an ordinary stick, thrown down casually upon the ground. For periscopes, too, we also used imitation stakes placed naturally in the barbed-wire entanglements. The British on occasions used imitation trench telephone poles to mask their periscopes.

The Dijon shop turned out large numbers of silhouettes and dummies. They were drawn from life by artists at Dijon and then cut out from ordinary wall board. Soldiers of the Fortieth Regiment posed as models for these silhouettes. All sorts of postures were employed, but nearly all of them represented soldiers in the act of climbing out of a trench or running, gun in hand, towards the enemy. The uniforms were painted in neutral shades, but the faces and hands were highly colored to be visible at considerable distances during the gray and mist of dawn, when silhouettes were usually employed.

The object of these dummy heads and silhouettes was to draw the fire of the enemy so as to make him reveal his strength and positions. The usual method of use was to place a number of silhouettes, possibly several dozen of them, in shell holes out in front of the trenches. The silhouettes were mounted so that they could be made to stand erect instantly whenever the ropes were pulled from the trenches. At the appointed moment the ropes would all be pulled at once, and the appearance to the enemy would be that of a raiding party starting out at top speed.

The British troops called this operation the Chinese attack. The Germans made no extensive employment of it. The silhouettes nearly always fooled the enemy, as indeed they would deceive anybody in such light and under such circumstances. The British were often amused to read in the German communiques that these Chinese attacks were regarded by the enemy as the real thing. More than one such "repulse" of silhouettes has gone down into the German records as a local success. On one occasion the Germans took a Chinese attack so seriously that they concentrated troops against it with the result that the British were able to gain considerable ground at the points weakened on both sides of the pseudo attack.

The Dijon factory made a thousand or so silhouettes, as well as a large number of dummy heads, these latter devices to draw the fire of snipers. These simulacra, however, had their principal use at the training schools in France, since they were peculiarly adapted to trench warfare, and by the time the American forces reached the front in strength the war of movement was in progress.

Several thousand sniper suits were turned out at Dijon. These suits were made of burlap, resembling in appearance the teddy-bear pajamas which little children wear. They were colored to match the terrain, either painted to resemble rocks or fitted with a grasslike covering. An adjunct to this suit was the cloth cover for the sniper's rifle.

Sniper suits were so deceptive that they would protect a man from observation even at short distances, and if exceptional care were used in the making of one, a man could conceal himself so effectually that an observer might step on him before seeing him. An American camouflage officer upon his return from France brought a sniper's suit with him and found a novel but practical use for it when he was invited to go duck hunting with a party of sportsmen. The other hunters stayed in their blinds, but the officer in the sniper suit went out in the open and shot more ducks than all the other gunners together were able to bring down.

The Dijon camouflage factory also turned out a large number of covers for the so-called Bessenaux hangars for airplanes. These hangars were large tents set up at aviation fields near the front. It was soon found to be impracticable to attempt to camouflage such tents by day, as they gave plenty of indication of their position in spite of the best efforts at concealment on the American and allied sides. However, the great danger at aviation fields came at night when the German bombing planes were abroad. Even on a dark night a white tent proved to be a good mark for the hostile airmen. Consequently the attempt was made to camouflage Bessenaux hangars at night only. It was found impracticable to paint the tents themselves, since the waterproof canvas would not take the paint readily. The solution was a large cover of burlap. This was painted in broken patches of color, much as artillery was painted in camouflage. At the factory such covers were spread out on the ground and painted with floor brushes dipped into water color.

All machinery at Dijon, with the exception of two lathes, two drill presses, and a shearing machine, was designed and built at the plant itself. The work of providing camouflage cover required enormous quantities of burlap to be cut up into strips. The English camouflage shops used stationary knives and a machine operated by a crank. American Engineers at Dijon designed a power-driven cutting machine with a large number of circular, whirling knife blades. The invention of this machine increases the production of burlap strips 900 per cent with the same force. The engineers at the plant also designed paint tanks and special machinery that would mix 4,000 gallons of color in a day.

There were about 1,000 French women employed in this plant. The executives paid great attention to their welfare. A special nursery, the "Creche," was built for their children. American Red Cross nurses cared for the babies during the time their mothers were at work. Many of the women employed were refugees driven from once comfortable homes. Their children fattened up with the good food provided by the army mess, and the mothers were correspondingly happy. Entertainments were frequently provided for the operators of the factories. The artists at the shop worked during their leisure moments and eventually produced the scenery and equipment for a genuine Yankee circus, animals and all, the menagerie, however, being made principally of papier-mâché with human operatives inside the beasts. The first performance of the circus was given on Thanksgiving Day, 1918, and the audience was so delighted that it demanded a repetition. After three encores of this sort it was suggested that performances be given in Dijon, a city of upward of 50,000 population, with admittance charged. This advice was followed, and the circus made such a hit that the Engineers were able to turn over to the French orphan fund a considerable sum of money.

CONCLUSION.

The foregoing account gives in a broad way an idea of the scope of activities and the achievements of the Engineers during the 19 months of actual warfare in France. To furnish the organization of technical troops and specialists which made all this possible, the original Engineer Arm of the United States Army was increased to 131.5 times its prewar strength, and the proportion of Engineer troops relative to the total forces was increased from 1.6 per cent to 10.8 per cent. To accomplish this, a heavy demand was made upon the technical professions and upon the industries of this country. In filling this demand most necessary assistance was given by the engineer societies and the engineering journals, whose patriotic work demands the highest praise.

In situations requiring special knowledge almost always there could be found some specialist capable of adapting himself and his work to the military needs. Engineer officers for the combatant regiments were younger members of the technical professions, who were sent to the training camps provided for the purpose and there given the essentials of strictly military knowledge. This training was later supplemented by courses in Engineer and line schools located in France. The training officers of the regiments were supplied from the Corps of Engineers, these men having both the military and technical knowledge fitting them for the command. The diversity of education and experience necessary in all branches of the Engineer service may be understood by a consideration of the duties of the different units sent to France during the war--specialist units, in addition to the strictly combatant divisional regiments, who also numbered among their commissioned and enlisted personnel many technical specialists of high attainment.

We had, for instance, seven railway construction regiments, two railway construction battalions, one regiment and five battalions for railway maintenance of way, two battalions for maintenance of railway equipment, four regiments and one battalion to operate our main military railways in France, three regiments to operate the light railways in France and their repair shops, two regiments for operating the regular railway shops, two regiments and six battalions for constructing buildings and other general construction work, two regiments for storing and transporting Engineer supplies, a forestry regiment, a light railway construction regiment, a regiment for building roads, a water supply regiment, a mining regiment, a quarrying regiment, a technical regiment for handling surveying, sound ranging, and location of enemy positions by means of special apparatus, three survey and printing battalions, two railway transportation battalions, an electrical and mechanical regiment, several companies to operate cranes, a camouflage service, five inland waterway companies, five ponton trains, a ponton park, a railway transportation and stores battalion, and a searchlight regiment.

Utilizing and applying the new knowledge and scientific achievements of recent years, drawing upon the fund of experience acquired by the Regular Army in its theoretical studies and past wars, making available the vast amount of technical skill which has assisted this Nation to its present commercial and industrial status, the Engineers of the United States Army worked and fought, planned, and accomplished in France a work which in magnitude exceeds any similar undertaking recorded in American history. From base port to first waves of an assault upon the enemy's position, Engineer troops have been constantly in action first to last and have "carried on" always with the high ideals of the profession and with the motto of the Corps of Engineers, "Essayons," before them.

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II. MILITARY RAILWAYS

In establishing contact between our great bases of supply on the French coast and interior points, as well as with the fighters in the various fields of operations, the Department of Military Railways of the Engineer Corps found it necessary to provide thousands of miles of railway track ranging from the standard gauge down to the narrow 60-centimeter type built right up to the border of No Man's Land, to construct and ship across seas thousands of almost every kind of freight cars, to build hundreds of locomotives and transport them to Europe, to provide in addition fabricated track that could be laid under heavy shell fire, and hospital trains that could care for our wounded.

It was on July 10, 1917, that Gen. Pershing cabled stating that the French had asked for 300 locomotives and 2,000 kilometers of track, in addition to numerous items of accessories that go with an order of this size. Delivery of the locomotives was requested by October 15, 1917, and of the track by December 31, 1917.

It was ascertained that the American Locomotive Works had built consolidation engines for France of an entirely satisfactory type, and that similar locomotives for the use of British forces on French soil had been turned out by the Baldwin Locomotive Works. After the decision to adopt the consolidation type of locomotive, which is generally used in freight service in the United States, arrangements were made at once with these two concerns to build 150 locomotives each.

The consolidation locomotive weighs 166,400 pounds, and is about the heaviest that can be used in France. It has one pair of engine truck wheels and four pairs of drivers. The engine is just as large as it is possible to use within the French tunnel and platform clearances. The type sent to France was, however, not nearly so large nor so heavy as the general run of freight engines used here.

The order for 150 engines was placed with the Baldwin concern on July 19, 1917, and the first locomotive of this order was ready for shipment on August 10, 1917, just 20 working days elapsing between the date of the placing of the order and the day when the first engine was completed and all set up ready for shipment.

This is believed to have established a new record for locomotive construction in the United States and probably in the world for an engine of this size. All the other locomotives in this order were delivered promptly--36 of the Baldwin engines being freighted from the factory in August, 71 in September, and the final 43 in October. Of the locomotives ordered from the American Locomotive Works, 133 were freighted in October and the remaining 17 in November.

On account of differences in the details of construction the original price fixed for the locomotives turned out by the American Locomotive Works was $51,000 each and for those of the Baldwin Works $46,000 apiece. Advance payments on these engines reduced the price by $1,000 each.

Changes in the painting and other small details resulted in a saving of $60 additional on each locomotive built by the Baldwin Works and $400 on each engine turned out by the American Works, so that the net cost of each Baldwin locomotive was $44,940, and of each American locomotive $49,600.

After much consideration, and after this initial order had been disposed of, it was determined that the Baldwin type of engine should be made the standard, and all subsequent orders for engines went to the Baldwin Works.

As orders were placed from time to time with the Baldwin people, reductions were made in price, so that the last engines of the total of 3,340 ordered from this concern were obtained for $37,000 each. Orders for 1,500 of these engines eventually were canceled without cost to the United States Government. The saving effected by the reduction in price on the engines ordered, using the original price as a basis of comparison, was $22,989,385.

There were shipped in all to the American Expeditionary Forces 1,303 locomotives, of which 908 had been put into service by November 11, 1918.

During the severe winter weather of 1917-18 and the simultaneous shortage of motive power on American railways, 142 of these consolidation engines built for the American Expeditionary Forces were turned over to the American railways to help out a critical situation in this country. It was possible to use these engines here by making changes in the couplers and some other slight additions to meet the requirements of our safety appliance laws.

At the time these engines were turned over to the Railway Administration we were producing locomotives for France much more rapidly than it was possible to provide tonnage to transport them overseas. These locomotives were in service helping out the transportation facilities in this country an average of 6 months and 28 days each before being recalled for shipment to France. They earned profits for the Government while in service for the Railroad Administration at the rate of 32.3 per cent a year.

It might also be noted that the Director General of Military Railways was appointed custodian of undelivered locomotives ordered by the Russian government from the Baldwin and American Works. In January, 1918, a total of 200 of these Russian locomotives was purchased, and the engines were converted to meet American requirements by a change in the gauge from 5 feet to 4 feet, 8½ inches, and a change in the coupling system to meet our standard. The price of these was $55,000 each. The Baldwin Works turned its 100 over to the Railroad Administration between February 3 and May 20, 1918, and the American Works made its deliveries between February 19 and May 30, 1918.

The combined cost of these locomotives was $11,000,000 and their total rental revenue from the railroads was $2,585,475 up to December 31, 1918, or 23.5 per cent of the cost price, or at the rental rate of 29.8 per cent per annum.

Orders for 90,103 freight cars to be used by the American Expeditionary Forces were also placed with American contractors. Of these the orders for nearly half--40,915 cars, in exact figures--had been placed just before the armistice, and these contracts were canceled at slight cost to the Government. Up to the end of the year 1918 a total of 18,313 freight cars had been shipped overseas, nearly all of these cars being of the 60,000-pound size. Close bargaining in the purchase of these cars resulted in a saving of $15,737,633 under the prices originally quoted.

For the first time in history American locomotives were shipped across the Atlantic stacked in ships on their own wheels. In our normal foreign trade, and even in the early locomotive shipments to the American Expeditionary Forces, both engines and cars had been disassembled at the seaboard and their parts put up in packages for convenient and economical loading on ships. Each of the first locomotives sent to France was crated in 19 packages, while the parts for an ordinary box car were put up in 26 packages.

On October 29, 1917, however, Gen. Atterbury called attention to the fact that the English were shipping locomotives across the Channel on their own wheels and stated that it would result in very great economies of time, money, and man power if such an arrangement could be made for shipments from the United States. Manufacturers of the locomotives, however, advised against this. So did our own embarkation people and the Shipping Control Committee. Efforts were unsuccessful to get car ferries from the Key West and Habana line and from Quebec for the transport of locomotives on their own wheels over the ocean.

Finally, however, after numerous efforts to get ships with large hatches the ore steamer Feltore was loaded with 33 locomotives on their own wheels, packed in baled hay. This steamer sailed May 18, 1918, and its arrival in France resulted in the following cable from Gen. Pershing:

Shipment of erected locomotives transmitted on the Feltore very satisfactory. Boat completely discharged of locomotives and cargoes in 13 days with saving of 15 ship's days in unloading the 33 locomotives erected as compared with same number of locomotives not erected and further saving of 14 days of erecting forces. Observations of Capt. Byron, who came with these locomotives, show that by loading locomotives in double tiers, placing cab parts and tools, now in separate packages, within tender space and fire boxes, 40 to 45 locomotives can be loaded.

Subsequently the steamers Cubore, Firmore, and Santore were assigned to the task of carrying these engines over on their own wheels. The total number of locomotives that went abroad in this manner was 533. After the signing of the armistice we sold the French Government 485 locomotives, of which 142 had been shipped up to January 1, 1919.

Efforts were likewise made to ship over freight cars already set up but this was also met with much objection. Finally, 1,000 cars were built to go over complete but the signing of the armistice stopped the shipment. The saving in the cost of shipping locomotives on their own wheels amounted to $775 for each one, and an average of $20 a car would have been saved by sending the cars over on their own wheels. But, in addition to this, the cost of erection on the other side, amounting to $800 for each locomotive, should also be added to the saving.

The number of cars actually shipped overseas for the American Expeditionary Forces, if made into one solid train, would be 140 miles long.

In August, 1918, there came a call from abroad to produce locomotives at the rate of 300 a month and freight cars at the rate of 8,200 monthly. Machinery for getting this production was started at once and was so effectual that during the months of September and October and up to the signing of the armistice engines were actually being produced and shipped from the Baldwin Locomotive Works at this rate. This company was turning out the greatest number of locomotives ever produced by any one company in the same length of time.

Arrangements for increasing production of freight cars to meet every possibility of tonnage facilities on the ocean were also made, and had the armistice not been signed we had planned to produce during the month of December 11,000 complete freight cars and to maintain this production rate until we had filled all orders from Gen. Pershing.

On our first purchase of rails, amounting to 102,000 tons, the price paid was $38 a ton for Bessemer steel and $40 a ton for open-hearth steel, as against a price of $59 a ton that the Russians were paying and prices between $54.36 and $61.87 that were being paid by the French. There was a saving in this item of approximately $2,040,000 as compared with the prices paid by the Russians and of $1,938,000 compared with the prices paid by the French.

In connection with our first purchase of this steel rail, it should be stated that the Lackawanna Steel Co. and the United States Steel Products Co. agreed to sell us rail on this basis. Orders were placed with these companies, but not with two other companies--the Cambria Steel Co. and the Bethlehem Steel Co.--who declined to accept the price offered.

All subsequent orders for steel rail were on the basis of $55 and $57 a ton for Bessemer and open hearth, respectively, which figure was established by the War Industries Board pursuant to the Government policy to stabilize industry by establishing fixed prices alike for all purchasers--the Government itself, the allies, and the public.

A total of 937 miles of standard-gauge railway track was laid in France with material shipped from this country.

A big money saving was effected by changing the design of the freight cars asked for by our overseas forces. Their original call was for 17,000 four-wheel cars of the French type, these varying from 10 to 20 tons capacity per car. Our investigations here convinced us that the American type of car with 30-ton capacity could be used on the French railroads. Consequently we recommended that 6,000 of the 30-ton American-type cars be sent abroad instead of smaller-capacity French cars. Our recommendation was approved by officers abroad, and as a result there was a saving of $12,640,000 in the cost of this initial order of cars. From that time all cars shipped from the United States were of the American 8-wheel type, a fact which resulted in a saving of approximately $189,600,000 over what it would have cost to build and ship the lighter French cars.

Had the light French type of cars, as originally suggested, been adopted, 270,309 cars would have been required instead of 90,103 cars, and probably twice as much tonnage would have been necessary to transport these cars overseas.

Most of the steel rails were purchased from the Cambria Steel Co., the Lackawanna Steel Co., the Bethlehem Steel Co., the United States Steel Products Co., and the Sweets Steel Co. Raised pier, gantry, and locomotive cranes were turned out by the several crane builders in proportion to their ability to produce. The Standard Steel Car Co. made millions of dollars' worth of metallic parts for freight cars, and the Colorado Fuel & Iron Co. produced rails and bars. As previously mentioned, the Baldwin Locomotive Works got the bulk of the orders for locomotives, although the American Locomotive Co., the Vulcan Co., the H. E. Porter Co., and the Davenport Locomotive Works also made locomotives for our Expeditionary Forces.

HOSPITAL TRAINS.

Ambulance trains were called for by Gen. Pershing in his cablegram of July 15, 1917. It was stated in this message that plans for these ambulance trains would be furnished by the Surgeon General of the Army.

To build these ambulance trains, with their complicated designs and specialized equipment, in this country would have entailed lengthy delay and very heavy expense, as after they had been constructed it would have been necessary to knock them down for shipment. With this fact in mind our officers here took up the question with Sir Francis Dent, of the British railway commission, who was in this country at the time. He stated that ambulance trains built by the London & North Western Railway, which had proved wholly satisfactory in three years of service, could be turned out by that same concern there quickly if the English design were adopted for our Army.

After considerable discussion and consideration the English design was followed, and orders for our ambulance trains were placed abroad. Up to December 7, 1918, there had been completed for our Army 19 of these trains, with a total of 304 cars, and there were in the course of completion at that time or under order 29 additional ambulance trains.

Information from England shows that it was indeed the part of wisdom to order these ambulance trains abroad, as figures from England stated that the first 14 of these trains were produced at a cost to us of £3,845 per car, including repair parts. This means that at the present rate of exchange the cost of each coach was $18,302.20, while to have built these cars in this country, knocked them down, and shipped them overseas would have cost $40,000 each.

NARROW-GAUGE RAILWAY EQUIPMENT--FABRICATED STEEL TRACK.

The urgent necessity for narrow-gauge railway equipment for our armed forces in Europe was first brought home to us when Gen. Pershing cabled on July 15, 1917. In this message he asked for large quantities of 60-centimeter locomotives, cars, and track. The types requested were entirely new in this country.

Specifically, there were required 195 60-centimeter steam locomotives with a low center of gravity and with a maximum of 3½ tons axle load; 126 40-horsepower gasoline locomotives; 63 20-horsepower gasoline locomotives; and 3,332 freight cars of various types, including box cars and flat cars of 10-ton capacity, tank cars, and dump cars. To aid in the building of this new equipment many photographs and designs brought over from France were used. It was decided to build the 10-ton cars fitted with small 4-wheel trucks at each end, rather than to make them of the 4-wheeled type, as with this construction they would be better adapted for the rounding of short curves.

In turning out the different kinds of locomotives for the 60-centimeter railways new designs were made in order to produce locomotives that would run with equal facility in either direction. For the gasoline locomotives, designs of types similar to standard-gauge engines, a few of which had been in the service in this country, were made, and orders were placed with the Baldwin Locomotive Works for the first lot.

The first steam locomotives were delivered by the builders on October 3, 1917, and the first gas locomotives on November 7, 1917.

Orders for the freight cars for these narrow-gauge railways were placed with a number of the larger car-building companies of the country. The first of these cars were delivered November 24, 1917.

When the armistice was signed a total of 1,841 locomotives and 11,229 cars of the narrow-gauge type had been ordered and 427 locomotives and 6,134 cars completed. Up to the 11th of November 361 of the locomotives and 5,691 of the cars had been shipped overseas.

Of the 361 locomotives sent to France, 191 were steam engines, 108 had 50-horsepower gasoline engines, and 62 had 35-horsepower gasoline engines. Of the 5,691 cars that went to the Expeditionary Forces prior to the signing of the armistice, 600 were box cars, 166 were tank cars, 500 were flat cars, 1,555 were 8-wheeled gondola cars, 330 were dump cars, 100 were artillery truck cars, 970 were motor cars, 180 were inspection cars, 300 were hand cars, and 990 were push cars.

For the construction of the narrow-gauge railroad used in the combat areas behind the front line trenches a special type of fabricated track was designed. This consisted of short sections of rail bolted to steel crossties. The American narrow-gauge railway was so arranged that it could be packed in knockdown shape to save shipping space. Most of this track was in 5-meter lengths, although many shorter sections were used. All, however, were in multiples of 1¼ meters, accurately sawed so as to insure absolute fit of intermediate sections when shell fire made replacement necessary. Vast quantities of curved track, as well as innumerable switches and turnouts, also were built.

In all about 605 miles of fabricated, narrow-gauge steel track were purchased and 460 miles shipped to France. All but 192 miles of the fabricated track was built at the Lakewood Engineering Co., near Cleveland. The balance was obtained through the United States Steel Products Co. The cost of the straight track was about $7,400 a mile, while the cost of the curved sections was $8,000 a mile.

Much of this narrow-gauge track that went to France was manufactured at the rate of between 5 and 6 miles of completed track a day.

Great quantities of the fabricated track produced by the Lakewood Engineering Co. were loaded upon camouflaged steamers in Cleveland in May, 1918, and sent direct to France, via Lake Erie, the Welland Canal, and the St. Lawrence River.

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III. ENGINEER ACTIVITIES AT HOME

A vast quantity of motorized or portable equipment was required by the Engineer units of the American Expeditionary Forces and this had in the main to be furnished under the supervision of the Engineers in this country. The extent to which this material was produced is shown by such items as 6,923 trucks of all kinds, 2,082 portable buildings, 124 portable shop and material trucks, 51 portable pile drivers, 90 electric storage trucks, 6,006 boilers, and 3,504 dump cars. Two-thirds of this equipment was shipped overseas before the armistice was signed.

The development of mobile shops was one of the most interesting phases of this branch of engineering work. Quite early in the war, when we began the construction of the great base shops in France, we developed these portable machine shops, blacksmith shops, carpenter shops, and storeroom shops in demountable truck bodies, to be used for general service in the field. The shops were so constructed that they could be entirely closed up when the unit was in motion; but when the shop was ready for use the sides and ends of the inclosing structure were lowered, forming work tables when the shop was left on the truck chassis. If the shop were entirely demounted, these sides and ends, let down, formed extensions of the floor. With this arrangement a wide range of general repair and construction work could be handled on the spot on short notice. If it were necessary for the shop to stay in one place for several days or weeks, the body could be demounted, and the truck chassis was then used for transporting materials to and from the shop.

Each portable shop contained about 800 different items of tools and equipment. Each was mounted on a 5½ ton truck. The portable machine shop contained a workbench, a drill press, a portable electric drill, a grinder, and a 14-inch lathe, these being operated by an electric power plant carried on the truck; and it also had an equipment of necessary small tools and supplies, including an oxyacetylene welding outfit.

The portable blacksmith, plumbing, and tin shops each contained a workbench, forges, hoists, pipe-fitting machines, a shear and punch, vises, and a welding and cutting outfit, together with a power plant and switchboard and the necessary small tools and supplies. The portable carpenter shop contained boring machines, a drill press, a bench grinder, a workbench, a saw bench, a winch, power plant and switchboard, small tools and supplies.

A complete machine shop on wheels cost the Government about $8,500. The carpenter shop cost $7,600. As supply units for the portable shops, the Government built 30 material trucks, each containing about 600 items of tools and supplies. These material trucks cost $6,100 apiece.

Another successful development of this nature was the portable photolithographic press truck, already referred to in the account of the American Expeditionary Forces' lithographic equipment. These automobile presses, which were at our front soon after our troops went into the trenches, were able to print and distribute lithographic sketches and maps within 12 hours after the original sketches were submitted for reproduction. The French and British armies also had mobile photolithographic units which were much less portable than ours and much slower in operation. The best time made by the French and British outfits was four days for the same work.

We also supplied to the Engineering forces abroad special water sterilizers and water tanks, mounted on trucks. The Engineers put small job-printing shops on trucks and photographic dark rooms on trucks for use in the field.

They equipped trucks with derricks, capstans, and wrecking machinery. They furnished automotive road sprinklers and oilers, as well as trucks with special dump bodies for highway work.

They developed a light, portable pile driver unlike anything used theretofore in commercial work. This machine was constructed of structural steel and had a total weight of 4 tons. It was mounted on a truck drawn by horses or mules, and the pile driver itself was operated by a 25-horsepower gasoline engine. The pile driver could be used within 16 minutes after its arrival at any point.

One development of this sort, the mobile clam-shell derrick, is worth noting. This unique piece of machinery was built by the Winther Motor Truck Co., of Kenosha, Wis. When the American Expeditionary Forces issued a requisition for 120 clam-shell derricks mounted on motor trucks, no such piece of equipment was in existence anywhere on earth. The Winther Co. volunteered to attempt to produce the machine. By giving a wider tread of rear axle to the Winther motor truck, the company could provide a suitable vehicle, but, search as they might, they could not find a derrick of sufficient power to operate a half-yard clam shell and also light enough to mount on a 7-ton truck. No such derrick existed. The company, therefore, without knowing anything about the manufacture of derricks, put its engineering force to work to produce a design. This design was developed in two weeks, and the derrick built from it was less than half the weight of any derrick of equal capacity. After being perfected, the mobile derrick in tests showed that it could move 350 cubic yards of sand or gravel per day or 500 or 600 tons of coal. One man could operate it and the motive power was a 4-cylinder gasoline engine.

The Engineering Department approved this design and ordered 32 such clam-shell units. Nine of these were delivered before the armistice was signed. The company has continued production of these derricks with a view of selling them to road builders and excavators in civil life.

For use of the various Engineer units we manufactured 1,610 tool wagons and shipped most of them to France. Because of the rough nature of the shell-torn ground over which these wagons must be used, we designed each to be uncoupled and operated as two 2-wheeled carts.

The development of mobile industrial units mounted on motor trucks is likely to have a profound effect on American industry in the future. For instance, the special derrick or crane trucks which we built are almost certain to be adopted in commercial use. The locomotive crane has always been a useful machine, but its chief use has been in handling heavy materials which were being loaded on or off railway cars. A crane which can be moved rapidly to places where railway tracks are not located should be of almost equal importance. An accompanying illustration shows in operation one of the derrick trucks which we built for overseas use.

In the same way the mobile pile drivers designed by the Engineer Corps should be of great future service in road building in this country.

The various machine shops which were built for war purposes will, in their duplications and adaptations, undoubtedly serve a useful purpose in future commercial activities in this country. The increased use of motive power on farms has created a demand for machine repairs. The day may come when the traveling machine shop will be a familiar sight on our rural highways.

The Engineer troops required a great quantity of hoisting machinery. Our purchases in this respect amounted to 700 cranes, mostly of the locomotive type, and 886 hoisting engines, at a total cost of $4,996,000. About two-thirds of this equipment was sent to France and installed at the ports of debarkation and at depots. The rest was used at the shipping points in this country. This machinery was of great aid in the rapid handling of materials at tidewater.

A vast amount of small tools and construction material was required.

Some 21,000 tons of barbed wire, shipped abroad to be used principally in the construction of entanglements in front of American battle positions, were manufactured principally by the United States Steel Products Co., Jones & Laughlin, the Gulf States Steel Co., and the Colorado Fuel & Iron Co., although several other firms also supplied barbed wire.

The Engineering Department ordered in the United States, during the fighting, equipment and supplies which cost approximately $754,201,407.

We furnished in all 85,120 steel shelters of various sizes, of which 38,320 were of the individual type which could be carried by one man. The steel used in these individual shelters was about one-eighth of an inch thick.

There may be expected to be great incidental benefit to future American industry from improvements and inventions brought out by American military engineering in 1917 and 1918.

One important work, for instance, which the Engineer Department undertook was that of standardizing the requirements for paints and varnishes. At the outset our Army needs ran into 29 shades of color in 315 different paint and varnish mixtures. Without affecting any of our camouflage projects or other important undertakings, we reduced the number of shades required from 29 to 16 and brought the total number of commodities down from 315 to 99. This reduction in the range of commodities will be of great use to the paint and varnish industry in the future.

At the beginning of the war the mechanical rubber industry had but few standard specifications. The Engineers, after considerable research, developed 30 standard specifications for mechanical rubber goods, which class included such materials as hose, packing, and sleeves. The representatives of the rubber industry verbally stated that the Engineer Department in this short time did more good to the trade than it had been able to accomplish for itself in the previous three or four years of effort. Immediately after hostilities stopped rubber concerns began asking the Engineer Department for its standard specifications.

In the manufacture of hardware and kitchen utensils there was also considerable standardization done, and changes in manufacturing methods were recommended which were put into effect by the producers. All spun goods were eliminated, and the industry confined itself to straight stamping, which meant a reduction in labor. A standard cobalt coating for enamelware was developed by which the industry conserved about 30 tons of nitre per month and made a more durable and satisfactory enamel coating, with the result that to-day the Army is purchasing its vast quantities of enamelware subject to certain tests, whereas, in the past, practically all this material was bought purely upon the manufacturers' statements. The shortage of tin was of considerable importance. Upon the recommendation of an Engineer officer enormous quantities of cafeteria trays were coated with zinc and large amounts of tin thereby conserved. The finished tray was entirely satisfactory and gave essentially the same service as that plated with tin. Horseshoe nails, formerly a variable product, were standardized and tested, and methods were devised by which the Army was enabled to control their quality.

Before the war there was no standard rating for internal-combustion engines, each manufacturer rating his motors according to his own ideas. Our studies of small engines of the type used for driving pumps or operating woodworking and metal-working machines resulted in many improvements, which have been adopted by the manufacturers of internal-combustion engines. Out of these studies came the so-called army rating, a standard which is bound to result in the more careful rating of commercial engines.

The Engineer Department brought out a modification of the design of the existing line of gasoline-driven shovels by applying caterpillar traction to the larger sizes, thus doing away with the labor required to plank up and block shovels that move on wheels.

When we entered the war, the explosive trinitrotoluol was standard for our Army for mining and demolition purposes. The Bureau of Mines, in cooperation with the Engineer Department, developed an explosive which is cheaper than T. N. T. and promises to replace it for engineering operations.

We also improved the devices commercially used in electrical detonation of distributed charges, our improved detonators being more certain and reliable than anything in use.

Commercial machines for detonating as many as 250 standard No. 8 caps were developed for the Panama Canal, but the machines in common use had seen little improvement for 25 years. As a result of the development by the Engineer Corps, a machine capable of detonating 120 caps was obtained, weighing no more than the 30-cap commercial blasting machine and costing slightly less.

A second machine was developed, capable of exploding 500 caps, at a price not greatly above the price of a 30-cap commercial machine. Mining engineers who saw this development stated that it would have a high commercial value, as these improved machines would make electric blasting more positive and dependable than any other form of detonation, as well as making it possible to set off a large series of charges simultaneously. The Panama Canal machine weighed 35 pounds and cost $126. Our 500-cap machine weighed 30 pounds and cost $35. The du Pont 30-cap machine weighed 25 pounds and cost $25. Our small machine weighed 20 pounds, cost $22.50, and would fire 120 caps.

In addition to this there might be mentioned other projects developed primarily for war purposes but which will be available for the industrial uses of peace. These included portable well-drilling outfits of a new type, alcohol stills of a small size for the utilization of waste products in small units, sound reducers on the exhaust pipes of gasoline engines, air strainers to minimize the chances of dust and grit entering gasoline engines. When the war ended we were working on the problem of hastening the setting of concrete and were also studying the production in this country of photographic colors and tone chemicals formerly secured only from Germany.

In general, mention should be made of the exhaustive tests in many industries conducted by the Engineer depot and by special detachments of Engineers. Tests were made of hundreds of pieces of apparatus, and these tests led to many improvements in American manufacture. Illustrating how these tests were regarded by individual concerns, the Cleveland Tractor Co., after a test of its equipment conducted by Army Engineers, stated: "Our people consider this test to be the most valuable ever undertaken by this company." This is indicative of benefits scattered throughout American industry by the engineering war tests.

While practically all of the research work which resulted in the developments and improvements noted was conducted by Engineer officers while on duty at the General Engineer Depot in Washington, since the transfer of the functions of the General Engineer Depot to the Division of Purchase, Storage and Traffic, November 1, 1918, much of this research work has been and still is being carried on by the latter division.

For handling Engineer materials there were established the General Engineer Depot at Washington, D. C, embarkation depots at South Kearney, N. J., and Norfolk, Va., and shipping depots at Baltimore, Md., Philadelphia, Pa., Jacksonville, Fla., New Orleans, La., and Mobile, Ala. In addition, subdepots were organized at all of the divisional camps and cantonments.

The war demanded the production in America of quantities of precision instruments. These were required not only by the Ordnance Department for the equipment of artillery with sights and indirect fire-control apparatus but also by the Engineer Corps, the Signal Corps, the Bureau of Aircraft Production, and the Medical Department. These instruments were such things as aneroid barometers, pocket compasses, measuring tapes, surveyors' equipment generally, map-drawing outfits, draftsmen's supplies, and so on. For a large period of the war the procurement of precision instruments was in the hands of the General Engineer Depot. Later, when the War Department's supply activities were being consolidated, the purchasing of precision instruments, except the highly technical sound-ranging devices, was taken over by the Director of Purchase and Storage, the organization of the General Engineer Depot going along in the transfer. The development and the production of searchlights and sound-ranging apparatus remained in the hands of the Engineer Corps.

In April, 1917, there were probably not more than a dozen recognized American manufacturers of high-grade precision instruments. As an indication of the expansion of manufacturing capacity required by the war, one concern, the Taylor Instrument Cos., of Rochester, N. Y., which had manufactured in peace times watch-pocket compasses at the rate of 15,000 a year, were called upon to turn them out at the rate of 10,000 weekly to fill an order for 200,000 of them. In order to handle this contract the Taylor Instrument Cos. built a new factory building in 20 days. A certain type of aneroid barometer required by the exigencies had never before been produced in America. The Taylor Instrument Cos. succeeded in producing 1,240 of these barometers.

The Lufkin Rule Co., of Saginaw, Mich., was called upon to manufacture 700 band chain measuring tapes for surveying, graduated throughout according to the metric system, and also 1,240 special outfits for repairing such tape. These band tapes when broken are fastened together by tiny rivets, which are produced by special machinery. Because of the inability of the machine-tool industry, swamped as it was with war demands, to produce the special rivet-making machines, it was necessary to reduce in the specifications for repair outfits the quantity of metal rivets for each kit from 4 ounces of rivets to 2 ounces.

Field artillery required a precision instrument known as the miniature telescopic alidade of the Gale type. It is unlikely that 150 of these instruments had been made in the United States during 10 years, yet the Artillery demands called for the production of 1,110 of them. The W. & L. E. Gurley Co., of Troy, N. Y., not only manufactured half of this order, but, in order that the Government might obtain a sufficient supply of these instruments, it turned over to a competing firm, the Eugene Dietzgen Co., of Chicago, the lenses, prisms, hermetically-sealed bubbles, and other parts for 555 instruments.

The Army required large numbers of hand tally registers to be used by checkers and observers. The Benton Manufacturing Co., of New York, had been making less than 15,000 registers of this sort in a year, yet it increased its facilities and turned out 62,000 of them for the Army within two months.

The Army required 35,000 complete sketching outfits for the use of military observers. The contents of these outfits were manufactured by a dozen different concerns.

Drawing instrument sets were produced by the Eugene Dietzgen Co. Each set included a pair of proportional dividers. Our draftsmen had always obtained their dividers from Europe. The divider, which nearly everyone has seen, appears to be a simple device, yet it must be made with the utmost precision, or else it is valueless. In manufacture it goes through more than 100 distinct factory operations.

Marching compasses for troops were made by the Sperry Gyroscope Co., of Brooklyn, N. Y., the quantity in manufacture being over 200,000 instruments.

Many other delicate instruments of most difficult manufacture, whose description is too technical to be set down here, were produced successfully in America during the war period.

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IV. SOUND AND FLASH RANGING AND SEARCHLIGHTS

In childhood we were enthralled by the tales of those magic persons whose keen hearing could detect even the whisper of the growing grass. As camouflage developed, modern warfare yearned for such supernatural gifts of sense that troops might detect the unseen presence of the enemy. Accordingly Science, the fairy godmother of today's soldiers, raised her wand, and lo, the Army was equipped with the wonderful ears of the fairy tale, uncanny no longer, but a concrete manufacturing proposition.

Artillery practice nowadays abhors the wasted shot. The time when cannon fired in the general direction of the enemy, and hoped to hit something, passed when the long-range rifles and howitzers, with their marvelously accurate sighting instruments, came into existence. Whole books have been written on the subject of pointing a modern cannon in the modern way. A great proportion of our industrial effort in the recent conflict was devoted to the sole end that we might aim our artillery accurately.

For instance, to this end almost exclusively was devoted the enormous production of aircraft material. The observer in the airplane or balloon trusted not to his eyes but to the finer sight of the photographic camera; and this again occasioned a large war industry--the production of cameras and their operation in the field, which included the production of finished photography in the field dark rooms. But, as the airplane and aerial camera were perfected, camouflage was undertaken as a protection from discovery from aloft; and so might be brought in another chapter--the production of camouflage material and the work of camouflage experts in the field. Presently camouflage succeeded in baffling the camera to a great extent, and this made necessary the development of instruments that could detect the location of the enemy by sound. Since the unaided ear was not keen enough to supply the desired information, applied science came to the rescue with the various devices embraced in the general classification of sound-ranging equipment. The production of this equipment was under the direction of the Engineer Department of the Army.

In three classes of military work we needed hearing refined to the razor-edge. With keen enough ears we could detect those subterranean operations of the enemy known as mining; with ears of that sort we could detect and locate the positions of hostile cannon; and still again we could employ such sensitiveness of hearing to find in the darkest sky at night the hostile raiding airplane.

One of these long-distance ear drums which man invented for himself as an aid to his military operations was known as the geophone. The first geophone used by the western powers in the war was invented by the French. It was a simple mechanism. The device or drum which received the sound waves and magnified them consisted of a small closed box with a confined air space. This box was weighted with a leaden disk to give it the required inertia. The geophone was placed upon the ground and the vibrations of the earth were communicated through the medium of the confined air space. The sounds then reached the listener's ears via a rubber tube and an ordinary stethoscope horn. By means of this device the slightest vibrations of the ground were rendered audible.

The geophone was used to detect enemy mining operations. The listener placed the weighted box on the floor of an underground gallery or on solid earth or rock. If the enemy were burrowing in the ground anywhere within a distance of 75 yards the geophone would tell about it. In order to enable the listener to know in what direction the sounds came, two geophone boxes were provided, one connected with each ear. By placing the boxes a small distance apart from each other and them moving them until the vibrations in both ear horns were equalized, the listener could tell approximately in what direction the enemy mining operation was located.

Geophones were used by both sides, and so effective did they prove to be that it is reported that they were largely instrumental in stopping mining operations altogether. If an enemy mine were located by one of these devices, a counter mine could be started at once and carried through, usually with disastrous results to the hostile miners.

As our first step in the production of geophones, we adopted the French device; but later on we developed an instrument with nearly one-third greater range than the French geophone had. This improvement was developed by the Engineers and bureau specialists at the Bureau of Standards in Washington with money provided by the Engineering Department. We produced the improved model in sufficient quantities to meet the requirements of the American Expeditionary Forces.

We also developed an electromechanical geophone that could be connected up by wire to a central listening station some distance back from an exposed location. The sound-receiving boxes or microphones were placed out in No Man's Land and hidden under trash or earth. They were so sensitive that they would not only record any subterranean activities of the enemy within their range, but at night would betray enemy raiding parties attempting to cross to our positions, the sensitive boxes picking up the vibrations of their speech or footsteps. The central listener could locate approximately the position of hostile operations by observing which boxes were receiving the sounds in greatest intensity. The boxes could also pick up and send to the central listening stations conversations carried on by the enemy parties even in low tones, the apparatus thus acting as the dictatorship of the war.

But by far the most important work done by listening instruments was in locating the positions of enemy gun batteries. This was one scientific instrument, at any rate, which the Germans were never able to produce successfully for themselves. During the final months of the war more enemy guns were located by listening instruments than by any other means. An American instrument with the Army spotted 117 German gun positions in a single day by surface sound ranging. This was the high American record set in the war, but at all times our sound-detecting equipment had an uncanny accuracy. Up to the end of the fighting, no way had been discovered to conceal the location of a gun from sound-ranging instruments suitably placed and properly operated.

The instruments used for locating gun positions were of such a highly complicated and technical nature that no one but designers and mechanics skilled in the production of complex electrical equipment could build them at all. The recording instruments, or microphones, were of a sort so delicate that their use theretofore had never been considered outside of laboratories. Yet they were required to operate successfully amid the din and concussion of heavy bombardments. All useless sounds and jars were filtered out so that only the sought-for vibrations could come to the central recording mechanism.

Studies of gunfire showed that when a cannon fires an explosive shell of high velocity there are three distinct concussions. One of these is the sharp crack produced in the air when the shell, dragging a short vacuum trail behind it, passes over the head of the observer. As the air rushes into this vacuum and collides with itself, it produces a crack that is similar in origin to ordinary thunder. The second concussion to be heard is that produced at the muzzle of the gun by the expanding gases that propel the shell. There is still a third, the break, or explosion. In order to locate a battery or gun exactly only one of these concussions--the explosion at the muzzle of the gun--must be picked up by the microphone. The first and third shocks, and all other sounds not useful to the work should be damped out and excluded.

A number of these microphones would be placed in scattered positions, usually in a trench, and then connected with the central recording mechanism. When a microphone picked up a hostile gun explosion the disturbance was instantly transmitted through several miles of wire. An ingenious and complicated mechanism actuated an electromagnetic needle, which instantly recorded this disturbance on a tape of photographic paper, calibrated to show fifths of seconds in time. Each microphone on outpost duty was represented on this tape by a parallel line; and, as six microphones were usually used, the tape was striped with six parallel lines. As the other microphones at the front picked up the concussion of the gun, their records were made on their respective lines; and the observers at the central station, by noting the difference in time between the reports of the various microphones, and by making calculations based on the rate at which sound travels, could locate the gun that set up the disturbances by means of ordinary surveyor's triangulations. So accurately would this mechanism do the work that a gun position could be determined within 50 or 60 feet.

Incidentally, it is interesting to note that the practice of our Army was to secure in advance, by means of surface sound ranging and other methods, the positions of all the enemy's guns that could be learned. Then, often after intervals of hours or even days, the fire began simultaneously upon all these gun positions just as our attack started.

In this country we had two experimental stations for the development of sound-ranging apparatus. We began experiments in this work in June, 1917. Before we had perfected any satisfactory instruments, the British had met with great success with the Bull-Tucker system; and we adopted that type for the use of the American Expeditionary Forces. From plans and models sent to this country we produced an American Bull-Tucker machine, utilizing standard American electrical equipment wherever we could. At the close of the war we had in operation along the American front 12 complete American outfits. The six microphones of each recording machine in action were set about 5,000 feet apart along the front, so that each sound-ranging section covered a frontage of approximately 5 miles. The 12 outfits in use were sufficient to locate the guns of the enemy on a 60-mile front.

About a month before the fighting stopped we sent to France a new model sound-ranging set which had been developed with the cooperation of the Bureau of Standards. The reports from the American Expeditionary Forces indicated that this American development was superior in several important particulars to anything else in use when the war came to an end. The American instruments were lighter, easier to carry about, easier to install, and much cheaper than those of the British type, and would operate under more adverse weather conditions. The impulses received by the microphone in this equipment were recorded on a running tape smoked by an acetylene flame.

Sound ranging for the detection of airplanes at night requires an equipment which consists fundamentally of a sound-gathering device and a listening mechanism, the combination enabling the observer to tell the direction from which the sound is coming. When a bombing plane approaches at night the hum of the motor can be heard at a distance from 1 to 3 miles, or even more, depending upon conditions. But the direction of this sound is elusive to the unaided ear, as anyone can testify who has heard an airplane in broad daylight but could not locate it with his eyes. Before the invention of aerial sound ranging the searchlights hunting for the hostile airplane were obliged to sweep the sky aimlessly in an endeavor to locate it; and the pilot of the plane could often maneuver to keep out of the light. But by use of the sound detectors not only can the approach of the airplane be detected at a distance beyond the hearing range of the unaided ear, but, what is more important, its direction can be determined within an angle of 3°. The use of these sound detectors greatly increased the chances of locating airplanes at night by searchlight.

The Engineer Department conducted extensive experiments in the development of aerial sound detectors. One form developed consisted of a set of long horns with listening tubes attached to the small ends and leading to receivers on the observer's head set. These horns were mounted on a turntable which the observer could revolve, so that the horns could be turned in the general direction of the sound. Four horns were used in this mechanism--two to indicate the direction of the airplane on a horizontal circle (in azimuth), and the other pair to indicate the direction on the vertical arc (in elevation). Under favorable conditions the sensitiveness of this device was three times that of the unaided ear, and the airplane could be located within an angle of 1°. The horn detector, however, was large and cumbersome and not satisfactory for a mobile unit.

For field sound ranging, when the listener may wish to move from place to place, the parabloid sound reflector was developed. This hemispherical object, like a huge fountain basin in shape, was made of material similar to building board and shaped in parabolic lines. Such a sound collector echoed or reflected the sound from every point of its surface to a focal point where the listening instrument was located. The observer turned the parabloid on its universal mount until the sound was equalized in his ears, and then the exact direction of the airplane would be indicated by the azimuth and elevation pointers on the machine. The paraboloids developed by our Engineering Department had a sensitiveness three times that of the unaided ear and could locate sound within 3° of arc.

We were not pioneers in developing the parabloid, however, the French having built them ahead of us; but our apparatus possessed marked advantages over that of the French. In the first place, the French collecting device weighed 3½ tons and was so heavy and cumbersome that it could scarcely be moved at all. The total weight of the American collecting device was only 1,300 pounds. The American instrument was thus much lighter and more portable. It was so simple that it could be set up in about one-sixth the time that it took to erect the French device. The cost of our machine was only about two-fifths that of the French mechanism.

Although valuable work in detecting gun positions was done by sound ranging, yet both sides located guns by watching their flashes. We improved flash-ranging sets of the allies. These were simple in principle. A number of observers at posts commanding good views were equipped with observation telescopes mounted on tripods to watch for the flashes of enemy guns. Whenever two or more of them observed the same flash and reported its direction, the position of the gun could be determined by ordinary triangulation.

However, in operation the system was not so simple, because of the fact that the observers reporting might not have turned their instruments upon the same flash. This difficulty was met by furnishing each observer with an outpost switch set. As soon as he observed the flash through his telescope he closed the switch, and that action turned on a small electric light at the headquarters station, which might be miles away. Then, as soon as he could, he telephoned in the direction of the flash observed. If the operator at the switchboard saw two or three of the lights flash simultaneously, he knew the observers at the front had probably caught the same flash. Lights that came on a little ahead or a little behind the simultaneous lights were disregarded when the observers telephoned reports.

In developing the telescope for this system considerable difficulty was experienced on account of the shortage of the proper optical glass in this country. We were, therefore, obliged to buy our telescopes in France until our supply would be available. These telescopes were expensive mechanisms, and in some of the work of the flash-ranging sections two of them were originally required at each observing station--one to determine the position of a shell burst in elevation and the other its position on the horizontal circle in azimuth. Since the declaration of the armistice an American Engineer officer has designed a telescope eyepiece which enables this work to be done by observing through a single instrument, thus effecting a marked saving in the number of telescopes which might be required in the future.

When the fighting stopped our military scientists and others cooperating with them were developing a type of ground sound-ranging apparatus which it was hoped could be utilized to give troops warning of the firing of heavy artillery shells in their general direction. Preliminary experiments show that at a distance of 4.1 miles this mechanism could record the firing of a gun some 19 seconds before the arrival of the shell. Under proper circumstances this elapsed time would enable troops properly warned to seek cover from the explosion of the projectile. This development of sound-ranging apparatus and its application to the protection of personnel was made possible by the far greater speed with which shock vibrations travel through a dense medium like the earth than through the usual sound-conveying medium, the atmosphere.

SEARCHLIGHTS.

The searchlight equipment of the United States Army prior to 1914 consisted chiefly of lights located at our coast defenses. In 1916 we began the development of mobile searchlight-and-power units for field-army work, four horse-drawn equipments, with 36-inch lights, being ordered first, and later eight other sets, with extensible towers and gasoline electric generators. When the war was approaching we ordered 85 sets of the limber-and-caisson type. The caissons of these sets carried 24-inch lights on extensible towers. In January, 1917, we ordered 50 high-intensity lights to replace as many low-intensity lamps at our seacoast fortifications. The first war order was placed in April, 1917, and consisted of 20 additional searchlights of the 60-inch dimension, the largest light ordered by the War Department.

After the entrance of America in the war the Engineer Department began studying the requirements abroad for searchlights used in defense against hostile aircraft; and in September, 1917, this investigation resulted in orders for 360 high-intensity searchlights, 693 high-intensity arc mechanisms, and 1,000 glass mirrors of standard design.

About this time we began looking to the improvement of existing searchlight equipment. The cooperation of leading scientists, manufacturers, and Government bureaus was obtained, and the product of exhaustive experiments was 18 different new kinds of searchlights either partially or wholly developed.

The first of these were produced, shipped, and were in operation with the Second Field Army in France on October 1, 1918. This was a new form of searchlight more powerful than any that had been produced before that time. It weighed one-eighth as much as lights of former design, cost only one-third as much, was about one-fourth as large in bulk, and threw a light 10 per cent stronger than any other portable projector in existence.

Without going into the details of this mechanism its most striking innovation, from the standpoint of the nontechnical observer, was the absence of the front glass through which the beams of the older type lamps are sent. The absence of the glass, while reducing the weight and cost of a light, also increased the intensity of the beam of the searchlight, since any glass, no matter how conducive to rays, absorbs light to a considerable extent.

In the first part of the war we took the 36-inch lights which the Government had on hand and mounted them on motor trucks. For generating power for the lights, motor trucks were equipped with electric generators operated by the crank-shaft of the truck engine. In moving about each truck carried not only the light and power unit and accessories, but provided space for the crew and their equipment.

When we went into the war there was only one firm in the United States that could make the large searchlight mirrors, but two other concerns developed the art and the faculties during the hostilities. These mirrors were of glass and cost about $1,000 at prewar prices. The maximum output in the United States before the war was three 60-inch mirrors per week. As the result of governmental encouragement the production of the 60-inch mirrors increased until it reached the stage of 15 a week in November, 1918; and the price was reduced to about $900 per mirror, even under war-time conditions with respect to labor and material. This was equivalent to a price of about $700 per mirror under normal conditions, or a saving of 30 per cent.

A remarkable contribution of the United States to searchlight science was the production of a satisfactory metal mirror for projecting the beam. The metal mirror not only weighed a little less than the glass mirror, but it cost only one-third as much as the glass one, could be produced in one-fifth the time, was much less fragile, and extended the possibility of manufacture to a wide number of industries. The metal mirror possessed 97 per cent of the reflectivity of the glass mirror. This slight dullness is inappreciable in searchlight work and more than compensated for by the other qualities of the metal reflector. This type of mirror, however, had not yet been put in production when the war ended.

Our inventors during the 19 months of hostilities succeeded in reducing the size of carbons used in 200-ampere lamps from 2 inches in diameter to 1-1/8 inches. This cut the cost of carbons in two, but the improvements tripled the amount of light developed.

In November, 1918, we were working with assurance of success to develop a simple system whereby field searchlights could be pointed and controlled from a distance. Such controls had been used in experimental work prior to 1917, but the mechanisms were complicated and not suitable for field service.

The searchlight section of the Corps of Engineers also developed optical finding devices, which doubled the range of all searchlights without requiring any modification of the lights themselves. Neither the ordinary telescope nor night glass is suitable for target finding by searchlight. The result of our investigation was the development of a combined observer's chair, eye protector, and searchlight target finder, the new equipment adding only 10 per cent to the cost of the searchlight unit.

The range of our modern high-power searchlight, whose target is a ship at sea, is about 15,000 yards; the range of this searchlight when its target is an airplane is about 15,000 feet.

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I. TOXIC GASES

The first recorded use of suffocating gases in warfare was about 431 B. C., sulphur fumes having been used in besieging the cities of Platea and Belium in the war between the Athenians and the Spartans. Similar uses of toxic substances are recorded during the Middle Ages. In August, 1855, the English Admiral Lord Dundonald, having observed the deadly character of the fumes of sulphur in Sicily, proposed to reduce Sebastopol by sulphur fumes, and worked out the details of the proposition. The English Government disapproved the proposition on the ground that "the effects were so horrible that no honorable combatant could use the means required to produce them."

That the probable use of poison gases was still in the minds of military men is evidenced by the fact that at The Hague conference in 1899 several of the more prominent nations of Europe and Asia pledged themselves not to use any projectiles whose only object was to give out suffocating or poisonous gases. Many of the Powers did not sign this declaration until later. Germany signed and ratified it on September 4, 1900, but the United States never signed it. Further, this declaration was not to be binding in case of a war in which a non-signatory was or became a belligerent. Admiral Mahan, a United States delegate, stated his position in regard to the use of gas in shell, at that time an untried theory, as follows:

The reproach of cruelty and perfidy addressed against these supposed shells was equally uttered previously against firearms and torpedoes, although both are now employed without scruple. It is illogical and not demonstrably humane to be tender about asphyxiating men with gas, when all are prepared to admit that it is allowable to blow the bottom out of an ironclad at midnight, throwing four or five hundred men into the sea to be choked by the water, with scarcely the remotest chance to escape.

The Second Hague Peace Congress in 1907 adopted rules for land warfare, and among them was article 23 which read as follows: "It is expressly forbidden to employ poisons or poisonous weapons."

The use of toxic gas in the great war dates back to April 22, 1915, on which day the Germans employed chlorine, a common and well-known gas, in an attack against the French and British lines in the northeastern part of the upper Ypres salient.

The methods of manufacturing toxic gases, the use of such gases, and the tactics connected with their use were new developments of this war; yet during the year 1918 from 20 to 30 per cent of all American battle casualties were due to gas, showing that toxic gas is one of the most powerful implements of war. The records show, however, that when armies were supplied with masks and other defensive appliances, only about 3 or 4 per cent of the gas casualties were fatal. This indicates that gas can be made not only one of the most effective implements of war, but one of the most humane. It will, of course, be necessary to remove the noncombatant population from a greater depth of country immediately in the rear of the fighting lines than formerly, in order that women and children may not be gassed. This additional sacrifice of territory for war uses is another element of effectiveness in the weapon.

Since Germany had chosen to utilize toxic gas in warfare, the allied nations were compelled to adopt like tactics; accordingly England and France, faced with the desperate situation resulting from advantages secured by the Germans through the employment of these new weapons, immediately turned their attention not only to devising methods for protecting their own troops, but also to securing supplies and equipment necessary for the utilization of toxic gas as an agent of warfare against the German Army.

Germany originated thereafter the use of most of the new forms of gas, but the allied nations and America were actually producing, at the time of the armistice, gases on a much greater scale than Germany was ever able to attain. In fact, America itself was producing gases at a rate several times as great as was possible in Germany.

Prior to the entry of America in the war our overseas observers had been collecting information bearing upon gas warfare, referring the facts so obtained to the Ordnance Department in Washington, where the information was turned over to Lieut. Col. E. J. W. Ragsdale, who was then in charge of the Trench Warfare Section.

In the early days of our belligerency it was seen that we should need a plant for filling artillery shell with toxic gases. The Government in the fall of 1917 bought a large tract of land near Aberdeen, Md., to be an artillery proving ground. Approximately 3,400 acres of this reservation, about one-tenth of it in area, was set aside as the site for the gas shell-filling plant. This reservation was known as Edgewood, and the plant erected on the site was called the Edgewood Arsenal. Work started on the construction of the arsenal on November 1, 1917.

None of the toxic gases in use in Europe, except chlorine and small amounts of phosgene, had ever been commercially prepared in the United States. It was the original intention to interest existing chemical firms in the manufacture of these gases; but there were many difficulties in the way of such a project, not the least of which was the ruling of the Director General of Railways that such products as poison gas be transported only on special trains.

Also we discovered that the private chemical companies were loath to undertake such manufacture. The exhaustive investigations necessary before quantity methods of manufacture could be devised would be uncertain and expensive. There would be great danger to the lives of those employed in such work. Many of the private concerns were already crowded with war work. Finally, the new plant equipment which must be set up would be worth nothing when the war ended, since the manufacture of such gases would be limited to the period of hostilities. These and other considerations explain the reluctance of the commercial chemical industry to undertake the production of war gases.

Consequently the Government was forced to adopt the plan of building various chemical plants at the Edgewood Arsenal in connection with the filling plant. By December 1, 1917, it had been decided to build at Edgewood a chlorpicrin plant and a phosgene plant. The contracts were immediately let, and the work was pushed through the rigorous winter of 1917-18.

In March, 1918, the Edgewood project was taken from the Trench Warfare Section of the Ordnance Department and made an independent division under the command of Col. Wm. H. Walker. In June, 1918, the Chemical Warfare Service was organized, and the Edgewood Arsenal was transferred to it. Gen. W. L. Sibert, Director of the Gas Service, took charge of the activities of the arsenal in May prior to the official transfer.

Chlorine, the raw material for the manufacture of which is common salt, was one of the principal materials required in the gas-production program. Although chlorine was a standard product in the United States prior to the war, it was soon seen that we had an inadequate commercial supply to meet the requirements of our proposed gas offensive. Chlorine was used not only by itself, but it was also the active agent in the manufacture of nearly all the other toxic gases which we required. Consequently we decided to build a Government chlorine plant with two 50-ton units, giving a daily capacity of 100 tons of liquid chlorine. The ground for this plant at Edgewood was broken on May 11, 1918, and the actual production of chlorine begun on September 1.

In July, 1917, the Germans introduced the so-called mustard gas. It was immediately realized that for certain purposes of fighting this chemical was the most effective product so far employed, and a large number of Government experts here at once concentrated their energies in developing methods for its manufacture on a large scale. Not only were the uniformed experimenters busy at the Gas Service's American University Camp, at Washington, D. C., but experimental units were established at the plant of the Dow Chemical Co., at Midland, Mich., at the plant of Zinsser & Co., Hastings-on-Hudson, N. Y., and at the Government plant which had been started by the Trench Warfare Section, at Cleveland, Ohio.

Eventually it was decided to erect a large plant at Edgewood for the manufacture of mustard gas. Not until April, 1918, however, did we feel that we possessed sufficient knowledge and information to justify the construction of a mustard-gas plant on a large scale. France and England also were long in working out satisfactory methods of mustard-gas production. We began to make mustard in June, and continued with rapidly increasing output until the signing of the armistice.

It soon became evident that we could not depend upon civilian labor in the operation of the various chemical plants at Edgewood because of the danger involved. It was decided, therefore, to utilize enlisted men in the working crews. As the projects at Edgewood increased in size and number, the forces at the arsenal grew, until at one time there were 7,400 troops at this point.

Meanwhile the Government had at last been able to persuade a number of private chemical firms to manufacture toxic gases. The Government agreed to finance all new construction, but the operation was to be in the hands of the contracting companies. At each plant the Government stationed one of its representatives with necessary assistants. In the spring of 1918, these scattered factories by official order were made part of the Edgewood Arsenal, each plant being designated by the name of the city or town where it was located. Thereafter in Army usage the term "Edgewood Arsenal" embraced not only the group of factories on the Edgewood reservation, but also included the following projects:

Niagara Falls plant, operated by the Oldbury Electro-Chemical Co. Project--the manufacture of phosgene.

Midland, Mich., plant, operated by the Dow Chemical Co. Project--the sinking of 17 brine wells for the purpose of securing adequate supplies of bromine.

Charleston, W. Va., plant, operated by the Charleston Chemical Co. Project--the manufacture of sulphur chloride.

Bound Brook, N. J., plant, operated by Frank Hemingway (Inc.). Project--the manufacture of phosgene.

Buffalo plant, operated by the National Aniline & Chemical Co. Project--the manufacture of mustard gas.

In addition to these, the Edgewood Arsenal built at points advantageous to supplies of raw materials four other plants, and operated them as well. These were as follows:

Stamford, Conn., plant. Project--the manufacture of chlorpicrin.

Hastings-on-Hudson, N. Y., plant. Project--the manufacture of mustard gas.

Kingsport, Tenn., plant. Project--the manufacture of brombenzylcyanide.

Croyland, Pa., plant. Project--the manufacture of diphenylchlorarsine.

In constructing and equipping the Edgewood Arsenal we laid 21 miles of standard-gauge railway and 15 miles of narrow-gauge railway, built nearly 15 miles of improved roadway, and set up two water systems, one with a capacity of 1,500,000 gallons per day for the manufacturing purposes of the chemical plants, and the other providing a fresh-water supply pumped 4 miles with a daily capacity of 2,000,000 gallons. In all 558 buildings were put up on the grounds of the arsenal. There were 86 cantonment buildings, with a capacity of 8,400 men, as well as adequate quarters for officers and civilian employees. Three field hospitals, a complete base hospital, and separate buildings for Y. M. C. A. and K. of C. activities indicated the extent of the building equipment. Three power houses were provided, with a total capacity of 26,500 kilowatts.

In the construction of buildings every precaution was taken to avoid accidents from the handling of toxic gas, the ventilating systems being as near perfection as human science could make them. It is notable that out of the thousands of men employed only four met their death by gas poisoning. Three of these casualties were due to phosgene and one to mustard gas.

To show that all of the danger of the war was not confined to the front, the following table of casualties in 1918 at the Edgewood Arsenal proper is here given:

-----------------+------+------+-----+------+-----+-----+-----+------- Toxic agent. |June. |July. |Aug. |Sept. |Oct. |Nov. |Dec. |Total. -----------------+------+------+-----+------+-----+-----+-----+------- Mustard gas | 14 | 41 | 190 | 153 | 227 | 47 | 2 | 674 Stannic chloride | | 3 | 8 | 15 | 21 | 3 | | 50 Phosgene | | | 3 | 7 | 2 | 17 | 1 | 50 Chlorpicrin | | 14 | 18 | 9 | 3 | | | 44 Bleach chlorine | | 2 | 39 | 2 | 1 | | | 44 Liquid chlorine | | 1 | 3 | 2 | 7 | 5 | | 18 Sulphur chloride | | | 2 | 1 | 6 | | | 9 Phosphorus | | 2 | 7 | 5 | 1 | | | 15 Caustic soda | | | 3 | | 3 | 4 | | 10 Sulphuric acid | | | 4 | 3 | 1 | | | 8 Picric acid | | | 2 | | | | | 2 Carbon monoxide | | | | | 1 | | | 1 +------+------+-----+------+-----+-----+-----+------- Totals | 14 | 63 | 279 | 197 | 293 | 76 | 3 | 925 -----------------+------+------+-----+------+-----+-----+-----+-------

As has been noted, chlorine was the only war gas produced on a commercial scale in America prior to the war. At the ordinary temperatures chlorine is a greenish-yellow gas of strong, suffocating odor. Through the combined effects of cold and pressure it is readily condensed to a liquid and is ordinarily shipped in this form, stored in strong cylinders.

Chlorine is prepared commercially by the electrolytic process. A current of electricity is passed through a solution of common salt. The greenish gas at once arises, leaving behind it a residue of caustic soda. The apparatus in which the salt is decomposed by the electric current is known as a cell. The Government plant used Nelson cells, each with a capacity of 60 pounds of chlorine and 65 pounds of caustic soda per 24 hours.

The Government chlorine plant at Edgewood was ready for operation in August, 1918, but was not actually started until September 1. The plant consisted of (1) a cell house, which had a total capacity of 100 tons of chlorine per 24 hours; (2) an electric substation for supplying the current; (3) a brine building, where the salt was mixed with water and the resulting brine purified; (4) a boiler and evaporation building, for concentrating the caustic soda from the cells; (5) a caustic fusion building, for drying the caustic soda and fusing it into solid form for shipment; and (6) a liquefying plant to condense and liquefy 50 tons of chlorine per day.

With the exception of chlorine, chlorpicrin was the first war gas to be manufactured on a large scale in this country. When pure, chlorpicrin is a colorless liquid which boils at a temperature approximately of 112° C. The compound has been known since 1848. While not so poisonous as some of the other products used in gas warfare, it is, nevertheless, an active poison, and has the additional advantage of being a fair lachrymator, or tear producer.

Chlorpicrin is made by the reaction between picric acid and chlorine. The chlorine is best supplied in the form of so-called bleaching powder, which is ordinary chloride of lime. In the manufacturing process as originally carried out, free picric acid was mixed with bleaching powder held in suspension with water. Later it was found advantageous to use calcium picrate instead of picric acid.

Accordingly, the final process was as follows: The bleaching powder was creamed with water and mixed with a solution of calcium picrate in large stills holding 5,000 gallons or more. A jet of live steam was then introduced at the bottom of the still, and the reaction began at once, the rapidity depending upon the amount of steam introduced. The resulting chlorpicrin, together with a certain quantity of steam, passed out of the still and was liquefied in the condenser. The resulting mixture of chlorpicrin and water was run into tanks, where the chlorpicrin, being insoluble in water, gradually settled to the bottom and was run off and used directly in gas shell.

In developing this process the Government was assisted by the Dow Chemical Co., the Semet-Solvay Co., and the American Synthetic Color Co., of Stamford, Conn., the principal work being done by representatives of the Bureau of Mines at the Stamford plant.

[Illustration: GAS CLOUD FROM 4.7-INCH GAS SHELL EXPLODING 8,533 YARDS AWAY FROM THE GUN AT LAKEHURST.] America's whole supply of chlorpicrin during the war came from the American Synthetic Color Co. and the Edgewood Arsenal. The Stamford plant was the first to reach large-scale production.

The contract with the American Synthetic Color Co. was dated December 13, 1917; and the company shipped over 111,853 pounds of the gas to Edgewood on March 11. This, when mixed with the necessary stannic chloride, supplies of which were already on the ground, was sufficient to fill approximately 100,000 75-millimeter shell. In the spring of 1918, due to certain internal troubles at the Stamford plant, it was agreed that the United States should lease this factory and operate it as a Government plant. Under Government operation the total production of chlorpicrin at the Stamford plant amounted to 3,226,000 pounds, of which 2,703,300 pounds were shipped overseas in 660-pound drums.

The chlorpicrin plant at Edgewood went into entire operation on June 14, 1918. Up to the signing of the armistice this plant had produced 2,320,000 pounds of chlorpicrin.

Phosgene was one of the deadliest gases employed in the war. Numerous other gases were used to annoy the enemy and force the wearing of masks, but phosgene was a killer employed to produce as many casualties as possible. The gas did not persist long in the air or on the ground after the shell had exploded, so that it was an ideal chemical for use in an attack. The gas would clear away by the time the troops following reached the place of gas concentration.

Phosgene at ordinary temperatures is a colorless gas, but it condenses to a liquid at 8° C. It is formed by the combination of two gases, chlorine and carbon monoxide, in the presence of a catalyzer. The reaction is best conducted in iron boxes lined with lead and filled with charcoal of proper quality, into which boxes a stream of the reacting gases, mixed in proper proportions, is introduced. The reaction creates heat, and means must usually be taken to keep the reaction boxes cooled. The resulting phosgene is condensed to a liquid by passing the gas through a condenser which is surrounded by brine kept cold by refrigeration. The liquid is then stored in strong steel containers or run directly into Livens drums or artillery shell.

Prior to 1917, the Oldbury Electro-Chemical Co., of Niagara Falls, N. Y., had set up a small experimental phosgene plant in the hope that the experiments might lead to the commercial utilization of carbon monoxide which was obtained by this company as a by-product in the manufacture of phosphorus. When we entered the war the company had developed its process to such efficiency as to warrant the construction of a large phosgene plant, and the Government entered into a contract with the company for the creation of facilities with a capacity of 10 tons of phosgene per day. Also, because of the great importance of phosgene in warfare, it was decided at the same time to build a Government phosgene plant at Edgewood. A little later the Government financed a phosgene plant at the factory of Frank Hemingway (Inc.), at Bound Brook, N. J.

The total output of the original small experimental plant at Niagara Falls, which was later leased by the United States, was 83,070 pounds of phosgene, of which 24,800 pounds were shipped overseas. The contract with the Oldbury Chemical Co. for its main phosgene plant was signed on January 15, 1918. Production here began on August 5 and by August 20 had reached a daily average of 5 tons. On November 1 the average daily production was 7 tons. The total quantity produced at this plant was 435 tons. The plant loaded 18,768 Livens drums with phosgene, each drum holding about 30 pounds. This plant was operated by enlisted men.

The contract with Frank Hemingway (Inc.) called for a factory producing 5 tons of phosgene per day by a secret process controlled by the company. The construction of the plant was begun on February 2, 1918, and phosgene was first manufactured on May 17. This concern reached its maximum of 5 tons per day by August 1, and produced in all 205 tons of phosgene.

Construction of the phosgene plant at Edgewood was begun on March 1, 1918. The plant consisted of four catalyzer buildings, each building having four units, each unit possessing a projected capacity of 5 tons of phosgene per day. The total capacity, therefore, was designed to be 80 tons per day. The carbon monoxide used in the process was produced by passing a mixture of oxygen and carbon dioxide over heated coke in a gas producer, the oxygen being supplied by a Claude machine with a capacity of 100,000 cubic feet of oxygen every 24 hours. The chlorine used came partly from the Edgewood chlorine plant and partly from outside sources.

The actual production of phosgene at Edgewood began on July 5, 1918, and worked up to an output of 20 tons per day by the date of the armistice. The total production of phosgene at Edgewood was 935 tons. The total output of phosgene from all three plants, Edgewood and the Bound Brook and Niagara Falls operations, at the date of the armistice was 35 tons per day; and this was increasing to reach 95 tons per day by May 1, 1919. The total phosgene produced by all the plants before the armistice was 1,616 tons.

The Germans, in spite of their attainments in chemistry, were never able to improve their clumsy and expensive methods of producing mustard gas. The best reports we have show that at the time the fighting ended, all of Germany's chemical warfare facilities could not produce more than 6 tons of mustard per day. The United States alone had ten times that capacity on the same date, while France and England both reached a heavy output. So concerned was the German high command because of the fact that Germany was being outdistanced in the production of mustard gas that the ablest spy of the German Empire was sent into France in October, 1918, to find out the French method of making mustard. One of the Chemical Warfare officers who accompanied our forces into German territory reported that the Germans had decided to adopt the American method of making mustard gas and to stop their former process.

Mustard gas was by no means a child of the great war, having been prepared in experimental quantities since 1886. It is a colorless, slightly oily liquid, boiling at 220° C. with some decomposition. When perfectly pure it freezes at 14° C.; but, since it usually contains small percentages of impurities, it usually remains liquid at 0° C, or even below that. In chemistry the substance is known as dichlorethyl sulphide.

The first commercial process proposed for the manufacture of mustard gas depended upon the use of ethylene chlorhydrin; and on April 13, 1918, a contract was made with the Commercial Research Co., Flushing, Long Island, for the manufacture of 10 tons per day by this process. In the spring and summer of 1918 a new process was developed both abroad and in the United States, one which used sulphur monochloride. Accordingly, the contract with the Commercial Research Co. was canceled, and efforts were concentrated on the later process.

This process consisted in blowing gaseous ethylene into liquid sulphur monochloride in large iron reaction vessels. The reaction developed much heat. Sulphur is set free by this reaction, and the temperature must be controlled in order to prevent the formation of solid sulphur in the reaction machine.

At the date of the armistice three mustard gas plants were either completed or nearing completion. The construction of the Edgewood plant was begun on May 18, 1918, and the first mustard was produced exactly a month later. The changing of processes, however, hampered production somewhat, but by September 20, the arsenal was producing 10 tons per day, and by November 11 had increased this to 30 tons per day. The total production of mustard gas at Edgewood during the war period was 711 tons, of which approximately 300 tons went into shell.

On July 8, 1918, the Government began the construction of a mustard gas plant at Hastings, N. Y. This factory was to have a capacity of 25 tons per day, afterwards increased to 50 tons per day. The first unit of this plant was ready to operate when the armistice was signed.

On July 6, 1918, the Government signed a contract with the National Aniline & Chemical Co., Buffalo, N. Y., calling for a mustard gas plant with a capacity of 50 tons daily. On November 11 this plant was 80 per cent complete. The cost of the plant was met by the Government, but the operation was to be in the hands of the Buffalo concern. The total daily capacity of all three plants when complete was estimated to be 200 tons.

To insure an adequate supply of sulphur monochloride for its mustard gas production the Government built a special plant at Edgewood with a capacity of 300 tons of sulphur monochloride per day.

As soon as toxic gas warfare had developed to a considerable extent, the perfection of gas-absorbing masks had given almost a complete protection against this new weapon, if the soldier put on his gas mask in time. But the mask, especially the earlier forms of it, was not easy upon the wearer, due to the difficulty of breathing through it and also because it restricted the soldier's vision. It was soon discovered that a force compelled to wear its gas masks for any considerable period lost in efficiency. The employment of gas by both sides for the purpose of forcing the opposite sides to wear masks continually was an important element in war at the close of hostilities.

For this purpose the so-called tear gases were produced. Gassing the enemy with tear gas was much cheaper than with poison gas, yet it forced him to remain masked. The tear gases were highly effective. Even a trace of tear gas in the air would in a few moments blind a man temporarily. A single tear-gas shell could force the wearing of masks over an area so wide that it would require from 500 to 1,000 phosgene shell to produce the same effect.

Most of the tear gases had bromine bases; so it was early determined that we should have to increase the American supply of bromine considerably if we were to meet our gas-warfare requirements. Bromine is a deep red liquid which boils at 63° C. The domestic source of bromine is principally in certain subterranean brines found in the United States, these solutions containing bromine in its compounds. The brines obtained in the vicinity of Midland, Mich., are especially rich in bromine, and by far the largest amount of bromine obtained in this country comes from that locality.

In December, 1917, at a conference with Mr. Dow, of the Dow Chemical Co., Midland, Mich., it was decided that the Government should finance the sinking of 17 brine wells near Midland, the Dow Chemical Co. to supervise the work and to produce the bromine from the brine. The work on this project was not begun until March, 1918, but the entire project was practically completed when the armistice was signed. This plant is a future war asset of the United States. It is capable of yielding approximately 650,000 pounds of bromine per year.

The tear gas which we prepared to manufacture was brombenzyl cyanide. It is a brownish oily liquid which solidifies to white or brownish crystals at 29° C.

The production of brombenzyl cyanide involves a fairly intricate chemical process. The first step is to chlorinate ordinary toluol, one of the coal tar bases, to produce benzyl chloride. This chloride is then mixed with sodium cyanide in alcoholic solution and distilled, benzyl cyanide being the result. It is then only necessary to brominate the benzyl cyanide by treating it with bromine vapor.

The first manufacture of brombenzyl cyanide in the United States was conducted at an experimental plant at the American University Station at Washington. After this a large scale plant was authorized at the plant of the Federal Dye & Chemical Co., at Kingsport, Tenn. The construction of this factory began on July 8, 1918, and operations started on October 29, the total production of brombenzyl cyanide being a trifle over 5 tons. In November the plant reached a capacity of 3 tons per day.

The bromine gases were not poisonous in the sense of being killers, but were merely highly irritating to the membranes of the eye. The killing gases were phosgene, chlorpicrin, and chlorine. Mustard gas in sufficient amount was also fatal, its effect being identical to that of a deep burn. It attacked the lungs, the eyes, the skin, and even the intestines if food contaminated with mustard gas were swallowed. An insidious feature of mustard gas is the fact that its action is practically always delayed. It might be several hours after a man was gassed, even fatally, with mustard before he became aware of it, and then it was too late to administer the treatment that might save his life. Goggles alone would have been sufficient protection against tear gas, except for the fact that it was invariably mixed with the deadlier gases.

The various experiments preliminary to our production of gases were conducted in provisional laboratories at the Bureau of Standards, Washington, D. C., Bureau of Mines, Washington, D. C., the Geophysical Laboratory, Washington, D. C., the Ohio State University, Columbus, Ohio, and Johns Hopkins University, Baltimore, Md. A control laboratory for the solution of problems arising in manufacture was eventually established at Edgewood. A total of 167,092 single chemical determinations were made at these laboratories under the direction of 20 commissioned officers, 45 noncommissioned officers, and 204 privates.

The production of gases and other chemicals was only part of the work of the Edgewood Arsenal and its subsidiary plants. The other chief activity was that of filling artillery shell with the toxic substances. The description of the plant which filled shell with phosgene will indicate the scale upon which this operation was conducted.

The empty shell, after being inspected, were loaded on trucks, together with the proper number of loaded boosters. The booster was the device which exploded the shell and scattered the gas. Electric locomotives then pulled the shell trucks to the filling buildings. There were four of these to a single shell-filling plant, radiating at right angles from a common center. From the trucks the empty shell were lifted by hand to a belt conveyor and the conveyor carried the shell slowly through a room kept cold by artificial refrigeration. Although the shell moved only 70 feet through this room the conveyor traveled so slowly that they were 30 minutes in transit, and during this time they were cooled to a temperature of about 0° F. This chilling was necessary because phosgene has a low boiling point, and it was necessary to keep the temperature of the metal of the shell considerably below the boiling point of phosgene in order that the gas might remain in liquid form while the filling was going on.

The chilled shell cases were next transferred to small trucks, each carrying six of them. The loaded truck was then drawn through a filling tunnel by means of a chain haul. This tunnel was so ingeniously contrived that the human assistance to the filling and closing machinery could all be conducted from the outside. The phosgene, kept liquid by refrigeration, was run into the shell by an automatic filler.

The truck was then moved forward a few feet to a point where the boosters were inserted into the noses of the shell by the hands of the operator reaching in through an aperture in the tunnel. The final closing of the shell was then accomplished by motors. The air in the filling tunnel was constantly withdrawn by strong ventilation, the exhaust air being washed in stone towers by chemical agents to neutralize any gases that might be present. The filled, inclosed shell were next conveyed to a dump, where they were classified and then stood nose down for 24 hours to test them for leaks. Then they were painted, striped, and stenciled by air paint brushes. The final process was to pack them in boxes and store them for shipment. This was done in large storage magazines on the grounds of the Edgewood Arsenal.

A similar method was used for filling shell with chlorpicrin, except that refrigeration was unnecessary. Mustard gas required another sort of filling machine.

Several filling plants were designed and constructed for filling grenades with stannic chloride and with white phosphorus, and also one for filling incendiary drop bombs.

The capacity of each of these plants per day was as follows:

Stannic chloride plant, hand grenades, 25,000. White phosphorus grenade plant, 30,000. White phosphorus smoke-shell plant, 155 millimeter shell, 2,000; or 4.7-inch or 5-inch shell, 4,000; or 75-millimeter shell, 6,000. Incendiary drop-bomb plant, 2,000.

The following sentences summarize the production and expectations of the Edgewood Arsenal:

(1) The gas program as of March 1918 called for approximately 545 tons of toxic gas weekly.

(2) The Chemical Warfare Service program of August 12, 1918, called for a much larger amount, viz, about 4,525 tons per week.

(3) The approximate filling capacity of the Edgewood Arsenal plant from August to November, 1918, was nearly 1,000 tons per week.

(4) The toxic gas production during this same period increased from 450 to 675 tons per week.

(5) The capacity of all projectiles received, unlimited by boosters, varied during the same period from 125 to 450 tons per week.

(6) The maximum capacity corresponding to boosters received was less than 100 tons per week.

In these facts it will be seen that the numbers of empty shell delivered to the plant was far less than the number required to accommodate the gas production. Many of the shell received were without boosters and therefore without value until boosters were provided, so that the limiting factor was really the supply of boosters. The booster supply was sufficient to take care of only a relatively small fraction of the toxic gas actually produced. The filling capacity of the plant was also in excess of the delivery of shell and boosters. The 75-millimeter shell-filling plant had a capacity of 1,200,000 shell per month, eventually double that, while delivery of shell was slightly over 300,000 per month and of boosters less than 200,000.

Because of the nature of toxic gas it is impossible to store it up in any large quantities. Early in the summer of 1918 large amounts were shipped in bulk overseas and there loaded into shell. Later we received instructions to stop all shipments in bulk except a limited amount of chlorine, and thereafter our production was limited to the number of shell and boosters available.

In June, 1918, we shipped in bulk 15 tons of mustard gas, 705 tons of chlorpicrin, and 48 tons of phosgene. This was to be exchanged for gas shell produced by the French. In late July the French had no more extra shell to be filled with American gas and this fact terminated the arrangement. However, we sold excess gas both to England and to France. England received 900 tons of our chlorpicrin and 368 tons of American phosgene. France took 300 tons of chlorpicrin and 1,408 tons of chlorine, equivalent to 1,226 tons of phosgene, since phosgene is 80 per cent chlorine including allowance for wastage in manufacture. France furnished phosgene shell to us in exchange for chlorine. In addition 200 tons of mustard gas were shipped to England and utilized by the English.

We therefore shipped to Europe in bulk 3,662 tons of gas or its equivalent, which gas was largely loaded in shell and used by the United States troops or those of the allies. This quantity was sufficient to load 1,600,000 shell, two-thirds of them being of the 75-millimeter caliber and the other one-third 155-millimeter, the total number being thought to be at least equal to the total number of gas shell fired by American troops in action. Thus while American gas was not actually fired in American shell against the Germans, American gas was used against the enemy and America furnished at least as much gas as she fired.

In addition to this we shipped 18,600 Livens drums loaded with phosgene. These contained 279 tons of gas, and some of them were fired at the enemy. We began producing loaded gas shell in the summer of 1918 and by August 9 had shipped 75,000 loaded 75-millimeter shell. These shell were unassembled for firing in the guns, the Ordnance Department having decided in June to assemble gas shell in their cartridge cases in France.

The Chemical Warfare production organization developed and manufactured a large number of special containers for the shipment of toxic gases. These were of special construction in order to guard against dangers that would result from leaks, and all had to stand the tests required by the Bureau of Explosives before they would be received for railroad shipment. The 1-ton containers, all of which would hold 1 ton of liquid chlorine, were designed by the Ordnance Department and would withstand a pressure of 500 pounds per square inch. The 300-pound phosgene cylinders, designed by the Ordnance Department, were made to withstand a 500-pound hydrostatic pressure and a 250-pound air test.

We purchased standard 55-gallon acid drums and standard-pattern cylinders for holding 75 pounds of chlorine.

We constructed chlorine tank cars, each tank with a capacity of 15 tons and a strength that could withstand a pressure of 500 pounds to the square inch. We also designed a tank car originally for the shipment of chlorpicrin and later used it for shipping sulphur monochloride.

CHEMICAL WARFARE PRODUCTION DATA.

Production of toxic material.

[All figures are for tons of 2,000 pounds.]

---------+-------+-------+-------+-----+--------------+-------+------+----- | | | | | | | | |Tita- 1918 |Liquid |Gaseous|Chlor- |Phos-|Mus- |Brom- |White | Tin |nium |chlor- |chlor- |picrin.|gene.|tard |benzyl |phos- |tetra-|tetra- |ine.[33]ine.[34] | |oil. |cyanide |phorus |chlor-|chlor- | | | | | | | | ide |ide. ---------+-------+-------+-------+-----+-----+--------+-------+------+------ January | | | 10 | | | | | | February | | | 27 | | | | 34| | March | 40| | 59 | | | | 74| 38| April | 176| | 33 | 15| | | 59| 116| May | 378| | 130 | 18| | | 70| 51| 50 June | 546| | 263 | 23| 6| | 60| 95| July | 512| | 499 | 100| 21| | 80| 112| 27 August | 243| | 646 | 314| 36| | 162| 94| 53 September| 438| 191| 564 | 327| 144| | 125| 96| 26 October | 242| 649| 445 | 664| 361| | 265| 75| 25 November | 148| 264| 100 | 155| 143| 5 | 77| 18| | | | | | | | | | +-------+-------+-------+-----+-----+--------+-------+------+------ Total | 2,723| 1,104| 2,776 |1,616| 711| 5 | 1,006| 695| 181 | | | | | | | | | Amount | 1,488| | 1,903| 420| 190| | 171| 106| shipped | | | | | | | | | overseas | | | | | | | | | Total | 895| 1,500| 1,500|1,050| 900| 90| 100| 91| 30 monthly | | | | | | | | | producing| | | | | | | | | capacity,| | | | | | | | | Nov. 1, | | | | | | | | | 1918 | | | | | | | | | Estimated| 1,100| 2,250| 1,500|1,650|4,000| 90| 100| 91| 30 capacity,| | | | | | | | | Jan. 1, | | | | | | | | | 1919 | | | | | | | | | ---------+-------+-------+-------+-----+-----+--------+-------+------+------

[33] Procured from commercial agencies.

[34] Manufactured at Edgewood.

Shell, grenades, Livens drums, and drop bombs filled.

---------+----------------------+-----------------+--------+---------------- | 75-mm. shell. | Grenades. | Livens |Incendiary drop | | | drums. | bombs. 1918 +-------+-----+--------+-------+---------+--------+-------+-------- |Chloro-|Phos-|Mustard | White | Tin | Phos- | | |picrin |gene | oil | phos- | tetra- | gene |Mark I |Mark II. | | | |phorus |chloride | | | ---------+-------+-----+--------+-------+---------+--------+-------+-------- July | 62,866| | | 8,696| 1,639| | | August |125,951| | |170,160| 56,763| 1,738| 350| September|110,358|1,988| 75,529| 51,421| 127,319| 6,355| | 1,998 October | 09,704| 12| 79,272|110,928| 147,669| 12,026| 184| 100 November | 15,892| 9| 224| 98,948| 30,386| 5,570| 8| 6 +-------+-----+--------+-------+---------+--------+-------+-------- Total |424,771|2,009| 155,025|440,153| 363,776| 25,689| 542| 2,104 | | | | | | | | Total |300,000| | 150,000|224,984| 175,080| 18,600| | number | | | | | | | | shipped | | | | | | | | overseas | | | | | | | | ---------+-------+-----+--------+-------+---------+--------+-------+--------

_Total monthly capacity of filling plants on date of armistice (Stokes shell, drop bombs, and other special containers not included)._

75-mm. shell (ultimate capacity) 2,400,000 4.7-inch shell 450,000 155-mm. shell 540,000 6-inch shell 180,000 Gas grenades 750,000 Smoke grenades 480,000 Livens drums 30,000

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