Military airborne radar systems

Front matter

declassified.

authority Secretary of

By

Foreword

T he first of the three projects initiated by the Microwave Section of the National Defense Research Committee in the summer of 1940 was the development of aircraft interception radar [AI] to permit successful attack of bombers by fighter planes at night or in overcast. Throughout World War II the development of radar equipment for military and naval aircraft was the major activity of Division 14. In addition to the laboratory development of radar equipment, Division 14 was directly concerned with the several other steps necessary for the introduction of new equipment to Service use, including experimental trial, engineering, consultation in the production on Service contract, acceptance and operational tests, installation as well as maintenance, modification, and other aspects of field service. It is logical, therefore, that in the Summary Technical Report of the Division program, one complete volume should be devoted to airborne radar.

The Division 14 Summary Technical Report consists of three volumes of which MARS is the second. The first volume, Radar, contains a summary of the Division 14 and Radiation Laboratory activities and special project reports. It will serve as a general guide to the Division projects and activities. The third volume is a complete bibliography of Division 14 and Radiation Laboratory reports listed by serial number, subject, organization, and in the case of Radiation Laboratory reports, by author.

The largest publication effort of Division 14 is the Radiation Laboratory Series published by the McGraw Hill Book Company, which is included as a supplement to the Summary Technical Report. This series consists of some twenty-eight volumes and an index. It is a complete report on the state of the radar art at the end of World War II, including texts on fundamental electronics, component and system design and engineering, peacetime applications, and Loran navigation.

A brief review of all the component and systems projects undertaken within Division 14 is given in the Final Project Report dated December 1945. The history of Division 14 and the Radiation Laboratory is told in the book Radar, published by Little, Brown & Company as a part of the Long History of OSRD.

The MARS volume was prepared for Division 14 by the Massachusetts Institute of Technology Radiation Laboratory. The Radiation Laboratory as the principal contract of Division 14 accounted for over

75 per cent of the Division’s dollar appropriations to contracts and participated in every phase of the Division program.

MARS may therefore quite naturally emphasize Radiation Laboratory airborne radar developments, its policies, and its opinions. It is not, however, limited to a discussion of Radiation Laboratory activities. Wherever desirable for a complete treatment of the subject, use has been made of material from the industrial concerns which participated in the development and production of the equipments on Army and Navy as well as on OSRD contracts. Also included is material received from Service laboratories, testing agencies, and operational groups, including principally the results of their experience in the planning, development, and introduction of new equipment. It has not been possible in most cases to make direct reference to the sources of material. The assistance of these many organizations which took part in the wartime radar program and contributed directly or indirectly to the preparation of this book is gratefully acknowledged. Specific acknowledgment is due to Bell Telephone Laboratories, Inc., General Electric Company, Galvin Manufacturing Corporation, Philco Corporation, Lukas Harold Company, and Radio Corporation of America.

MARS was written by members of the Airborne Division of the Radiation Laboratory with an Editorial Board consisting of F. R. Banks, J. J. Hibbert, L. J. Laslett, E. M. Lyman, Sims McGrath, R. M. Robertson, R. M. Thrall, and R. B. Whitney. Dr. Thrall was editor of MARS. He succeeded Dr. Laslett who as the first editor was responsible for the early planning and organization. It should be noted that the volume was written, after a short planning period, in less than four months. At this speed there was not sufficient time to permit all of the editing desirable. The individual authors of the various chapters were permitted complete freedom of opinion on controversial subjects such as the selection of equipment for future requirements as well as the most effective methods of test, introduction, and use.

A. L. Loomis Chief, Division 14

L. A. DuBridge Director, Radiation Laboratory

TITLES OF DIVISION 14 SUMMARY TECHNICAL REPORTS

SUMMARY TECHNICAL REPORT OF DIVISION 14, NDRC

Volume 1 Radar: Summary Reports and Harp Project Volume 2 Military Airborne Radar Systems (MARS)

Volume 3 Bibliography of Division 14 and Radiation Laboratory Reports

RADIATION LABORATORY SERIES (Published by the McGraw-Hill Book Company)

1. Radar System Engineering, Louis N. Ridenour

2. Radar Aids to Navigation, J. S. Hall

3. Radar Beacons, A. Roberts

4. Loran, J. A. Pierce, A. A. McKenzie, R. H. Woodward

5. Pulse Generators, G. N. Glasoe, J. V. Lebacqz

6. Microwave Magnetrons, George B. Collins

7. Klystrons and Microwave Triodes, D. R . Hamilton, J. K. Knipp, J. B. H. Kuper

8. Principles of Microwave Circuits, C. G. Montgomery, E. M. Purcell, R. H. Dicke

9. Microwave Transmission Circuits, G. L. Ragan

10. Waveguide Handbook, N. Marcuvitz

11. Technique of Microwave Measurements, C. G. Montgomery

12. Microwave Antenna Theory and Design, S. Silver

13. Propagation of Short Radio Waves, D. E. Kerr

14. Microwave Duplexers, L. D. Smullin, C. G. Montgomery

15. Crystal Rectifiers, H. C. Torrey, C. A. Whitmer

17. Components Handbook, John F. Blackburn

18. Vacuum Tube Amplifiers, George E. Valley, Jr., Henry Wallman

19. Waveforms, Britton Chance, F. C. Williams, V. W. Hughes, D. Sayre, E. F. MacNichol, Jr.

20. Electronic Time Measurements, Britton Chance, R. I. Hulsizer, E. F. MacNichol, Jr.

21. Electronic Instruments, I. A. Greenwood, Jr., D. MacRae, Jr., H. J. Reed, J. V. Holdam, Jr.

22. Cathode Ray Tube Displays, J. T. Soller, M. A. Starr, George E. Valley, Jr.

23. Microwave Receivers, S. N. VanVoorhis

24. Threshold Signals, J. L. Lawson, G. E. Uhlenbeck

25. Theory of Servomechanisms, H. M. James, N. B. Nichols, R. S. Phillips

26. Radar Scanners and Radomes, W. M. Cady, M. B. Karelitz, L. A. Turner

27. Computing Mechanisms and Linkages, A. Svoboda

28. Index

viii

PREFACE ?

T he primary purpose in writing the book, Military Airborne Radar Systems [MARS], was to put in permanent form a description of the status of radar for military use in airplanes, at the close of World War II. The book MARS consists of 24 chapters of which the first is general and the remaining 23 are divided into five parts. These parts represent a subdivision of military airborne radar systems into classes according to function.

Part I treats aircraft-to-surface vessel [ASV] radars. ASV comes first partly because of its historical position among radar systems but primarily because of the relative simplicity of the ASV systems. It is hoped that this simplicity will give the reader who is unfamiliar with radar systems an easy approach to the subject. The titles of the four chapters that comprise Part I indicate the major considerations which apply to all radar systems. These considerations are: (1) function of the system, namely, what the system is to be used for; (2) the theoretical basis for and general features of the system; (3) what things must be kept in mind in the actual design of the system once its general features have been decided; (4) how the system can be made to work and kept working and how well it does work.

Part II treats radar bombing. The opening chapter, Chapter 6, contains a summary of the part and a brief introduction to the geometric problem of bombing including a partial description of the theory and operation of the Norden bombsight. Chapter 7 treats the airborne radar systems used for bombing. Chapters 8 and 9 treat bombing computers to be used with these airborne radar systems. Not all bombing computers are discussed but enough are treated to give a fair picture of the state of the art at the close of World War II. Chapters 10 and 11 discuss groundaided bombing — beacon bombing in Chapter 10 and close-support bombing in Chapter 11. Chapter 12 treats toss bombing, a type of bombing used by fighter planes and light bombers. Problems of toss bombing are almost completely unrelated to those of the other kinds of bombing treated in the earlier chapters, being more closely related to the problems of fire control (see Part IV). Chapter 13 treats problems of assessment and training incidental to the successful use of radar for bombing.

Part III treats aircraft interception [AI]. Chapter 14 introduces the problem; Chapter 15 discusses the equipments used; and Chapter 16 deals with AI tactics.

Part IV treats airborne radar systems used for fire control. Chapter 17 is introductory in nature and emphasizes some of the problems encountered in the development of airborne radar fire-control systems. Chapter 18, “Automatic Following Equipment,” treats the most complicated of the fire-control systems. Chapter 19 treats a somewhat less complicated (nonautomatic) type of equipment. Chapter 20 treats radar systems used for range-to-target only. This includes systems suitable for ranging from one aircraft to another aircraft, systems suitable for ranging from an aircraft to a ground target, and systems which will do both. Chapter 21 treats computers (gunsights) to accompany the radar systems. Since very little of the computer work was done at the Radiation Laboratory [RL] there is very little discussion of specific computers in Chapter 21. The orientation of the chapter is toward the problems of combining radar systems and computing systems into overall fire-control systems. (Other volumes of the STR give quite satisfactory coverage and descriptions of specific computers. See the bibliography of Part IV.) Chapter 22 discusses the problems of assessing fire-control radar systems and is based on experiences of RL personnel, both at Service testing agencies and at the Radiation Laboratory.

Part V, airborne moving target indication [AMTI], treats a series of developments which came at the very end of the war. These systems show considerable military promise, but the treatment of them in the present volume is confined primarily to the technical details of the system.

The foregoing description of the various parts of book MARS does not give a complete picture of the purpose of the volume. We accordingly supplement the above part-by-part description with a discussion of the several theses of the volume and the places where these are treated. The basic purpose of the book MARS , as the general title Summary Technical Report implies, is to give a description of the status of airborne radar at the close of World War II. Realizing that the rapid rate of development of radar systems will make most of the systems in use during the war obsolete (in some cases even by the time this book is released) only a minimum number of systems have been described in detail. The reader is referred to the bibliography for detailed technical descriptions. The chapters which are primarily concerned with description of radar systems are 3, 4, 5, 7, 15, 18, 19, 20, 23, and 24.

IX

Preface

In many cases effective use of a radar system requires auxiliary computers. Given a radar system and a computer to go with it, it is then necessary to study the tactical importance of the combination. Discussions of tactics and computers come in Chapter 2 for ASV and in Chapters 8, 9, 10, 11, and 12 for bombing, in Chapters 14 and 16 for AI, and in Chapter 21 for fire control.

After a radar system and the appropriate attachments have been developed it becomes important to consider how the combination will function. It may be that several systems all designed for the same general function are offered to the Armed Services at approximately the same time. It is then necessary for the military testing agencies to conduct comparative performance tests so as to decide which of the competing systems should be developed. The importance of assessment is emphasized in Chapter 1; Chapter 22 gives a picture of the assessment situation for fire-control systems. In addition to assessing the systems, there is the major problem of assessing performance of military personnel being trained to use the equipment; this is discussed in Chapter 13, which also treats the general importance of an effective training program not only for operators but for maintenance men and staff officers as well. The problem of maintenance of radar systems as it concerns test equipment needed and procedures to be followed is discussed first (and in most detail) in Chapter 5 for ASV. Certain modifications for the more complicated radar systems are considered in Chapter 7 for bombing and Chapter 15 for AI.

Few of the staff members of the Radiation Laboratory realized when they entered the field of military research how long a road must be traversed in order to successfully introduce a new piece of equipment into military use. The initial thought of many a scientist was that a sufficient contribution would be to supply a laboratory model of the proposed new equipment. He realized that he might have to show the equipment to a representative of the Armed Services and later, perhaps, spend a few weeks with the engineer and the manufacturer for the equipment. In contrast to this early expectation, it was soon learned that the man who designed the equipment should follow it closely every step of the way. This includes, first, demonstrating the merits of the equipment to the Armed Services, which usually entails close cooperation with the military testing agencies; next, the designer must keep in close touch with the manufacturer and the Armed Services throughout the whole preproduction stage; he should follow his equipment into the training stages and then finally to the combat theater. The extent of participation by Radiation Laboratory personnel in these various phases is indicated in the summary report of Dr. L. A. DuBridge (see Volume 1 of the Division 14 STR). The chapters of the book MARS which treat the general position of the scientist in warfare and related problems are 1, 13, 17, 21, and 22.

The reader’s attention is called to the presence of the bibliography, glossary, and index at the end of the book. The arrangement of the bibliography and the notation for references are discussed at the beginning of the bibliography.

The table of contents indicates the author (or authors) of each section of the book. I wish to express my appreciation to all of the authors; to the members of the MARS editorial board, and especially to Dr. R. B. Whitney, who served as Associate Editor during the latter months of the preparation of this volume; and to the MARS production staff: Emily Blech, Doris Burton, Ann Klein, Jean McBeath, Pagonia Poulos, Jennie Scarponi, Bernice Zamett, for their cooperation and loyalty in the various stages of publication.

Finally, Division 14 wishes to state its appreciation to the U. S. Army and to the following organizations for permitting the use of their material in the illustration of this volume : Bell Telephone Laboratories, Galvin Manufacturing Corporation, General Electric Company, and the Sperry Gyroscope Company. The source of the figures is the Radiation Laboratory unless otherwise noted.

R. M. Thrall Editor iu } ribnv bsmhq bius ,bsjib3 <u n

This volume, like the seventy others of the Summary Technical Report of NDRC, has been written, edited, and printed under great pressure. Inevitably there are errors which have slipped past Division readers and proofreaders. There may be errors of fact not known at time of printing. The author has not been able to follow through his writing to the final page proof.

Please report errors to:

JOINT RESEARCH AND DEVELOPMENT BOARD PROGRAMS DIVISION (STR ERRATA)

WASHINGTON 25, D. C.

A master errata sheet will be compiled from these reports and sent to recipients of the volume. Your help will make this book more useful to other readers and will be of great value in preparing any revisions.

CONTENTS e

CHAPTER PAGE

1 Scientists in Warfare by M. G. White 1

Part I Radar Means For Detection Of Surface Vessels From Aircraft

By S. McGrath 7

2 Functions of ASV Radars by G. A. Garrett 9

3 Means of ASY Detection by G. A. Garrett , S. McGrath. . 13

4 Design Considerations by G. A. Garrett , S. McGrath . . 17

5 ASV Performance by S. McGrath, A. D. Cole, G. R. Banks 25

Part II Radar Bombing

By J. J. Hibbert 35

6 The Bombing Problem by W. J. Tull, S. McGrath ... 37

7 Airborne Radar Systems for Bombing by J. J. Hibbert,

D. Holliday, D. L. Hagler, F. R. Banks 47

8 Bombing Computers for Radar Mapping Systems by W. J.

Tull, D. L. Hagler, E. A. Luebke, J. J. Hibbert, W. Deerhake,

S. McGrath 66

9 The GPI Bombing and Navigation Computer by W. J.

Tull, N. W. MacLean 87

10 Beacon Bombing by J . B. Platt, R. B. Lawrance .... 104

11 Ground-Controlled Bombing by E. Lyman, G. D. Huff . 131

12 Application of Radar to Toss Bombing by L. J. Laslett . 139

13 Radar Bombing Assessment and Training by J. J. Hibbert,

G. E. Wheeler, J . E. Ward, T. A. Murrell, E. A. Luebke,

V. Holdam,, J. H. Buck, E. M. Lyman 155 xri

Part III Aircraft Interception Page

By R. McG. Robertson 173

CHAPTER

14 The Interception of Enemy Aircraft by R. McG . Robertson 175

15 AI Equipment by W. M. Cady , F. R. Banks 178

16 Aircraft Interception Tactics by F. R. Banks , T. W. Bonner 188

Part IV Airborne Fire-control Radar

•

17 General Considerations on Airborne Fire Control by R. M.

18 Automatic Following Equipment by H. G. Brewer . . . 200

19 Manually Directed Radar Gunsights by V. Holdam . . 219

20 Combined Optical and Radar Fire Control by E. H. B .

Bartelink 226

21 Computer Problems by R. M. Thrall 248

22 Assessment Problems by R. B. Whitney 256

Part V Airborne Moving Target Indicators

By E. M. Lyman 277

23 Basic Principles of AMTI by E. M. Lyman 279

24 Airborne Moving Target Indicator Systems by E. M.

Lyman 287

OSRD Appointees 320

Index 321

Chapter 1 SCIENTISTS IN WARFARE

1.1 GENERAL PURPOSE OF BOOK

This book on military applications of airborne radar systems is presented by members of the Airborne Division of the Radiation Laboratory with the hope that it will prove interesting and stimulating to those who take up our work as we disband. Our point of view in writing about radar systems is quite different from that adopted in the Radiation Laboratory Technical Series. a Where the latter series discusses technical design in detail and is intended to lay bare the scientific framework of radar, this volume treats the subjects from the overall operational point of view. If one compares the Technical Series to reports on medical laboratory research it would be appropriate to classify this present volume as a clinical study of the “patient-as-a-whole.” Throughout this presentation we emphasize the tactical requirements, the military problem, the reaction of the operators and, generally speaking, all those diverse human elements that only experience uncovers.

A book which deals in specific equipments runs the risk of becoming dated even before it reaches the public. The reader is urged to consider the following chapters as more than a mere history of airborne microwave radar from 1940 to 1945. They should be regarded as a study of the application of new scientific and technological developments to problems of warfare. Should war come again, some other powerful technical innovation may require the coordinated efforts of this country’s scientists, engineers, and military personnel. It is to be hoped that lessons learned in this war will not pass unnoticed and that the fumbling in the dark days of 1940-1942 will not be repeated. The reader should therefore pay close attention to the tactical thinking, to the general approach to the military problem in order to gain insight into the factors which made possible the development of so many important radars. Although the equipments to be discussed may well be stepping stones to the future, we regard the scientific point of view which this book tries to convey as more important than details of equipment.

a A technical series of approximately thirty volumes has been prepared by the Radiation Laboratory J staff for publication by the McGraw-Hill Book Oo.

1.2 SCIENTISTS AND MILITARY PROBLEMS

Before turning to specific military problems, we may profitably discuss the general relation between scientists and military problems, for this relation almost completely controls the degree to which the scientist can contribute.

Even a casual study reveals that big advances in tactical thinking and technical warfare have come from sources but very loosely tied to the military agencies. By the very nature of a major advance it is impossible to predict or “ whistle up” a revolutionary discovery. This holds for straight tactical, technical thinking as well as for basic science. It is necessary, therefore, to avoid excessive regimentation (often introduced in the guise of coordination or standardization) lest available national talent be too sharply directed into fields of short-range interest. For this and many other reasons it is best to rely upon civilian scientists in civilian institutions for the major technical and associated tactical advances. Obviously the detailed working out of tactical employment can only be done within the military structure, but even here World War II has demonstrated that civilian scientists belonging to civilian agencies must have the opportunity to introduce new equipment and even new tactical concepts at all levels of the military organization. Failure to recognize this function as legitimate has cost unnecessary delay, inefficient use, and even complete lack of appreciation of potentialities on the part of military agencies.

A book such as this is intended to be cannot present all the evidence in support of this thesis, but if any convincing is required, a comparison may be made between the wartime role of our American scientists and that of the German and Italian. Anglo- American science was essential to winning the war. Axis scientists were quickly surpassed by the victors, largely because the latter scientists were generally welcomed by the military at all levels even though they were associated with a separate organization in which they were free to work on new developments no matter how unpromising they appeared initially. There is little need to fear that free scientists, properly informed, will ignore the problems clamoring for

SCIENTISTS IN WARFARE attention; indeed there is more danger that they will be overly impressed by the current military problems and so fail to make revolutionary developments in advance of their need in battle.

According to all information available to us the Axis’ use of scientists was in sharp contrast to our policy. Second-rate scientists climbed into positions of authority and never gained the full confidence of the military, with the result that the scientists, being uninformed, indulged in many useless and fantastic enterprises. Exceptions, such as rocket development, do not alter the general belief that German scientists found little encouragement to consider themselves essential to the winning of the war. This was indeed most fortunate for us, as we now know after the events at Hiroshima and Nagasaki.

Axis scientists suffered either from over direction in government and industrial laboratories, or else had little contact with the military problem. True, the military agencies granted contracts to various institutional laboratories, but apparently very little of direct military interest was expected or delivered. This is in strong contrast with the way in which the Office of Scientific Research and Development organized and directed the work of American scientists.

1.3 THE SECURITY PROBLEM

As was pointed out, science in its military applications as well as in its basic form, must be a “free science” in order to be strong. If this is granted, several more steps should be taken by both military and scientific agencies. One has to do with the thorny question of secrecy. Contributing parties must be adequately informed about the tactical and technical problems. In spite of this obvious fact, there was far too much indiscriminate, blind classification of military information, scientific discoveries, technical equipment, and correspondence. Not only were our civilian scientists given too little access to military planning but they were also kept in mutual ignorance of scientific advances in cognate fields. Discoveries made in radar should have received much wider dissemination to those working in communications, television, underwater sound, and other fields. That these discoveries were not so distributed is a sad reflection on the scientists themselves who were temporarily forgetful of the very essence of creative thinking — freedom of publication. No one is suggesting unrestricted publication in the public journals, but surely there could have been a series of classified journals, available to all cleared scientists, which would have broken down artificial and highly injurious barriers. The writer has personal knowledge of many instances where greater restricted distribution of basic scientific and technological data would have profoundly increased our scientific strength.

With the coming of peace and talk about split-second pushbutton warfare of the future, we are faced with a most difficult problem in secrecy. In the midst of war it is clear that the best security lies in speed, in achievement, and not necessarily in secrecy. That secrecy can defeat its own purpose is shown by the frequency with which enemy scientists independently discovered techniques zealously guarded by us. Our secrecy merely slowed our own production and decreased our time advantage. A classical example is the case of the German Air Force which withheld information on captured British microwave bombing equipment from the German submarine command. Six precious months were thus lost by the Germans in combating microwave aircraft to surface vessel [ASV] radar. Perhaps the whole war and history of the world was affected by this instance of the shortsightedness of excessive secrecy.

Though wartime secrecy concerning engineering advances usually serves to keep the wrong people in ignorance, we must concede that peacetime secrecy is more of a problem. Here the element of time and speed is lacking; so if we assume that a truly important weapon can be kept secret there is point in limiting complete information to a few people only. Of course, such limitation will automatically retard technical progress, and perhaps retard quantity production in the event of war. But how can we assume that we can keep a secret, when in fact it is exceedingly difficult to find any important weapon or scientific advance that was not the contemporaneous interest of potential belligerents? This generally universal development of “secret” weapons should surprise no one, for creative thinking does not come as a bolt from the blue. It comes from the free interchange of ideas between all manner of people doing all manner of work. Modern radar owes much to virtually all nationalities working for hundreds of years. The atomic bomb roster includes Germans, Italians, French, English, Americans, Canadians, and Austrians, to mention but a few nationalities.

Before the war England, Germany, Japan, France, Italy, and the United States were all closely guarding radar as a highly secret device. By such close control our progress was immeasurably hampered, but to be

SELECTION AND TRAINING OF SCIENTIFIC PERSONNEL sure the enemy also probably failed to benefit from our discoveries. At the start of this war our radar was far behind what it could have been, but Japanese radar was still farther behind and that of the Germans somewhat ahead of ours. It is likely that our radar advantage over the Japanese would have been reduced by free publication, while it is interesting to speculate on how soon the whole show would have been given away anyhow under the impact of normal peacetime demands for the facilities which radar offers. The best one can hope for, even with tight security control, is a slight time advantage of a few months to a year or so and there is a very good chance, that excessive secrecy, by slowing down production, will actually lose any advantage gained by prior invention.

We can only conclude that in the past, and increasingly so in the future, no nation has had or will have a monopoly on scientific advance. No way is known to keep secret a fact of nature; it is present for all inquiring minds to discover and apply. Of nearly equally dubious validity is the belief that engineering “know-how” can be kept secret to the advantage of the possessor. Only rarely is an important weapon significant in small quantities, and if it requires mass production to be useful it must be designed with the national technical structure in mind. Airplanes, rockets, radars, guns, ships, tanks, radios are a clear reflection of our industrial life and as such hold few real secrets. In fact, our thinking is distressingly influenced by what has been done before, so that under the stress of war we turn again and again to established practice.

Wherein, then, does security lie? Some will argue that large standing armies and full military preparedness are the only safeguard. Others believe in a small, highly trained army of mechanical wizards possessed of an array of push buttons marked with the names of potential enemies. We even hear the attack-now theory which urges us to use our temporary alleged superiority in atomic bombs to wipe out anyone and everyone who might one day wipe us out.

To suggest that all this is unconstructive, hysterical, and even insane is perhaps out of place in a book devoted to the “creative” side of war. But as we remarked earlier, this volume attempts to approach warfare as a whole. By our intensive study of technical warfare during the most destructive war of modern times we, as scientists and engineers, are qualified to speak of more than boxes, knobs, rectifiers, and antennas. We have observed and reflected on the nature of technical warfare and can only conclude that no nation can, by scientific and industrial effort alone, insure itself against annihilation. There is no impregnable defense; there is no guarantee of victory no matter who starts another war.