The Elements of Field Fortifications: For the Use of the Cadets of the United States Military ...

Front matter

Google to make the world's books discoverable online.

It has survived long enough for the copyright to expire and the book to enter the public domain. A public domain book is one that was never subject

to copyright or whose legal copyright term has expired. Whether a book is in the public domain may vary country to country. Public domain books

Preface

This text-book is prepared for the use of the

c^ets of the United States Military Academy while pursuing their course of studies in the subject of

'* military engineering.**

The endeavor has been made to state concisely and plainly the principles upon which the "art of fortification'* is based, and to give all information likely to be of practical use to a young officer while serving in the field. All unnecessary details have been avoided, leaving explanations and illustrations of that kind to be introduced into the class-room.

The elementary form of the work and the method of treatment of the subject are based upon the assumption that the readers of the book are beginners and know nothing of the principles of fortification.

" Th$re are fiu things from which the tMier

never be separated: his gun, his ammunition, hii

knapsack, his rations for four days and an in-

Urenehing tool."

Nafolsoh.

Contents

CHAPTER L

Oeneral PrinoiplM and Definitions.

AmrtoLM. Pam

CHAPTER II. Slements of the Profile of a Fortifioation

18. The parapet 15

14. The terreplein 15

15. The.profile 15

16. Theberm 18

17. Theditch.. 18

18. The foot of a slope, the crest, etc. ... 18

19. The principal lines of the profile 1

Tl CONTSNTa.

CHAPTER III. Dimensions an^ Inclinations given to the Lines and Slopes

of a Parapet.

4RTICLB. PAOB

20. Height that a parapet should have 21

21. Definition of the terms, command and relief 22

22. Thickness that a parapet should have 22

23. Width and height of banquette 24

24. Inclination given to the interior slope 25

25. Inclination given to the superior slope 27

26. Inclination of the exterior slope 28

27. Width and uses of a berm 28

28. The uses, and the dimensions of a ditch 29

29. Slope of scarp and counterscarp « 30

30. Method of determining the dimensions to give the ditch 30

31. Method used in practice 32

82. The normal profile of a field fortification « 33

CHAPTER IV. The Trace of a Field Fortification

83. Definition of the terms, trace and sub-crest 34

84. The kinds of fire to which a fortification, or a body of troops may be exposed 34

35. The salient and re-entering angles of a trace 36

86. The general principles to be observed in the selection

of a trace 86

87. The reasons for observing these principles 87

CHAPTER V. Field Works

88. Classification of field fortifications into field works and lines 39

89 Classes of field works c. 39

OONTESfa. Til

40. Open, and half-closed field works 41

41. Lunettes 42

42. Bastioned front • 42

48. Closed field works 43

44. Redoubts 43

45. Star redoubts 44

46. Bastioned forts 45

47. Nomenclature of the bastioned fort 46

48. Sectors without fire, and dead spaces 47

49. Flanked dispositions 48

60. Relations existing between the different parts of a bastioned front 49

51. The least and the greatest exterior sides that can be used in bastioned fronts 51

52. Defects to be found in a bastioned fort 52

68. Defects of star forts 53

CHAPTER VI. Lines

64. Different classes of lines 54

65. What is meant by a continued line 54

66. What is meant by a line with intervals 64

Oontinned Lines.

67. Different kinds of continued lines 66

68. Tenaille line 56

69. Redanline 57

60. Indented lines 67

61. Bastioned lines 58

62. Advantages and disadvantages of continued lines 68

Lines with Intervals.

68. The positions occupied by the field works forming a line

with intervals 69

64. Thirdline .' 61

65. The advantages and defects of lines with intervals compared with other kinds of lines 63 nii OOl^TBNTS.

CHAPTER VII. The lize of a Field Work, the number of its OarrisoB, and

the Selection of its Trace.

ARTIGLB. PAOB

66. The size to give to a field work 64

67. The number of the garrison to defend a field work 65

68. The amount of space to be enclosed 66

69. The relation between the space, and the length of interior crest of a square redoubt when the number of the garrison is known 67

70. The things to be observed in the selection of trace 69

CHAPTER VIIL Oongtmction of Field Works.

71. The operation known as ** tracing " , 72

72* The operation known as " profiling ". 73

73. The method employed to construct the parapet 76

74 The time which is required to build a field work 78

CHAPTER IX. Revetments

76. What is meant by the term, revetment 81

76. Kinds of materials used for revetments 81

77. Fascines, and their construction 82

78. Fascine revetments 83

79. Gabions, and their construction 85

80. Hurdle revetments 87

81. Revetments of timber 87

82. Revetments made of planks 89

83. Revetments made with casks, barrels, etc 90

84. Sand-bags, and their use in revetments 90

85. Sod revetments, and their construction 02

86. Pisa revetment, and its construction 98

67. Revetments of other kinds 94

C0NTMNT8. it

OHAPTBB X.

Defilade.

88. What ii meant hj defilade, and Eow a field work maj

be defiladed 96

80 Plane of defilade, and its use 97

90 The amount of area to be defiladed 98

91. The method used to obtain the position of the plane of

9S. Front and reverse defilade 103

94. Methods used to defilade a work from reverse fires. . . . 104

95. The method used to determine the position of the plane

of reverse defilade 106

96. The method of defilade by means of traverses 108

97. Defilade of aline.. : 110

CHAPTER XL

The Interior Arrangements made in a Field Work. 96. Classes of interior arrangements 114

Arrangoment of the Parapet.

99. Arrangement of the parapet for defence 116

100. Barbette fire of artillery 115

101. Method of constructing the trace of a barbette 116

103. Pan-coup6, when used 118

103. Embrasure fire of artillery 120

104. Method of constructing the trace of an embrasure 121

105. Direct and oblique embrasures 124

106. Comparative advantages and defects pertaining to barbette and embrasure fires 125

107. Bonnettes, and their uses 125

108. Loop-holes, and their object 126

109. Traverses, their kind and their construction 128

110. Construction of splinter-proof traverses 180

111. Platforms for artillery in field works 182

Arrangements for Sheltering the Troops, etc. from -the effects

of the Bnemy's Fire.

112. Bomb-proofs and splinter-proofs for the use of the garrison 185

113. Method of constructing bomb-proofs 136

114. Blindages 138

1 15. Construction of splinter-proofs 138

116. Powder magazines 139

117. Service magazines, their construction 141

118. Gun-shelters 143

119. Materials used in construction of shelters 143

120. Example of a bomb proof used in the field works surrounding the city of Washington in 1861-5 144

131. Example of a powder magazine used in the same works 145

122. The position to be given to shelters of this class in a field work , 14*

Arrangements affording Communioationa, etc.

123. Passages leading into a field work, and where placed. . . 14^

124. The method used to conceal the interior of the work from being seen through the opening in the parapet. . . 148

126. Barriers, to close the passages 151

127. Bridges to cross the ditch 153

128. Ramps, their uses and dimensions 154

Arrangements for the Oomfort and Health of the Qanison.

129. Nature of the arrangements to be made 155

Other Interior Arrangements nsed.

130. Arrangements of a secondary kind 156

131. Block-houses, their dimensions and uses 157

132. Isolated block-houses 160

183. Stockades 161

CHAPTER XII.

Arrangements made Exterior to the ParapeL

184. Different kinds used exterior to a parapet 166

CONTENTS. XI

Ditch Defences.

185. Classes of defences used in the ditch 166

136. Caponni^res 167

187. Scarp and counter-scarp galleries 168

ObsUdei.

188. Two classes of obstacles 170

189. The ditches as obstacles 170

141. Entanglements 178

142. Chevaux-de-frise : 178

148. Palisading 174

144. Praises 175

145. Small pickets 175

146. Crow's feet, iron harrows ^ 176

147. Military pits, deep and shallow 176

148. Slashing of timber .. 177

149. Torpedoes 178

150. Stone-foagasses 179

151. Shell-foagasses 181

152. Inundations 181

158. General uses of military obstacles 182

CHAPTER XIII.

Application ol Field Fortifications to Sites upon Irregular

Ground.

154. The general considerations of the case 184

155. Three cases 185

156. Modification of profile caused 185

157. Modification of the trace 188

158. Defence of steep slopes 190

159. Defence of precipitous slopes 191

160. General plan of defence influences the engineer in the selection of the kind of works and the arrangement of these works to defend a position 191

Xn CONTENTS,

JSxldge Heads.

4BTICIjB. paoi

161. Bridge-head, its meaning 192

162. The object to be attained by the use of a bridge head. . 193

163. Strong bridge-heads, their use 195

164. Bridge-heads called horn works, crown works, etc 197

CHAPTER XIV.

Hasty Zntrenohments.

165. Hasty defences 200

166. Shelter-trenches, or rifle-pits 200

167. Construction of shelter-trenches 201

171. Use of shelter-trenches as covered oommanications. . . . 203

172. Trace of a shelter trench 205

173. Shelters for artillery or cavalry 206

174. Defence of a house 207

175. Tambours 208

176. Machicoulis galleries 210

177. Expedients similar in principle to a machicoulis gallery 210

178. Use of stone walls, hedges, etc., in defence 211

179. The defence of woods 211

180. The preservation and destruction of roads 213

181. Intrenched field of battle and example 213

CHAPTER XV.

Attack and Defence of Field Fortificatioiuu

182. The attack, when an assault, when a siege 221

183. Open assault, three periods of 222

184. Preliminary operations and the artillery attack 222

185. The operations of the second period 224

186. The operations of the third period 224

187. Attack by surprise 225

188. Unexpectedness of attack important to success 226

CONTENTS. xm

UPnoM. TAsm

289. Attack made by artillery only 226

190. Key point of position to be selected to attack 226

191 Defence of a field fortification 226

192. Memoranda furnished the commanding officers of the field works surrounding the city of Washington relative

to the defence 227

193 Examples of attack and defence of field fortification. . . . 237 194. The conclusion to be drawn from the history of assaults upon field works in recent wars «... 239

CHAPTER XVI.

Siege Works.

196. Siege operations 241

196. Investment 241

197. Posting the attacking forces 242

198. Lines of countervallation and of circumvaUation 244

199. Preliminaries 245

200. Selection of the side of attack 246

201. First parallel 247

202. Construction of the first parallel 249

203. Approaches 252

204. Flying trenchwork 263

205. The second and third parallels 254

206. Batteries 256

207. Construction of batteries 259

208. Remark upon construction of siege-works in advance of the second parallel 260

209. Maxims of Vauban .. 262

CHAPTER XVII.

MiUtary Bridges.

210. Communications of an army 265

211. How rivers may be crossed by an army 265

XIV CONTENTS.

ABTKJLK. PAttB

213. FerrieB 267

215. United States bridge equipage 269

216. Ponton bridge 270

217. Method used to build a ponton bridge 272

218. Description of the canvas ponton 274

219. Organization of a bridge train 275

220. Bridges built upon rafts 276

221. Bridges built upon fixed supports 277

222. Selection of points where a military bridge should be built 278

223. Preservation of military bridges *.... 280

224. Remark upon the advantages to be gained by reading works on the construction of military bridges 281

225. Examples of military bridges 282

CHAPTER XVm.

RailroadB.

226. Railroads as lines of communication 286

227. Construction of military railroads 286

228. Working of military railroads 287

229. Moving troops by rail 288

230. Preservation and protection of military railroads 289

231. Destroying a railroad 290

232. Remark upon the importance of having a good construction corps, and the use of the telegraph 295

Introduction

Iktuenchments are co-eval with man. In all agei they have played important parts in the contests carried on by force^ when men have striven for the mastery.

They have been recognized by the great masters of the art of war as important adjuncts of their military operations, and have been freely used by them in their campaigns.

Napoleon said^ 'Hhose who proscribe the help which the engineer's art may afford in the field, deprive them' selves voluntarily of an auxiliary force and expedient, nevei; hurtful, always useful, and often indispensable."

Frederick the Great, in his M^moires, says, — " Officers require different kinds of knowledge, but one of the principal is that of fortification.'^

General Sherman says in his memoirs, '^ earthforts, especially field-works, will hereafter play an important part in wars, because they enable a minor force to hold a superior one in check for a time, and time is a most valuable element in all wars."

The general of modern times who first prominently recognized the great merit of field works, and who saw

2 INTRODUCTION.

in them "an auxiliary force," was the emperor, Charles V. of Germany.

To each regiment of infantry he attached a hody of pioneers, oumbering four hundred, under the command of a special oflBcer, and provided them with intrenching tools. Those men were used to construct fortifications, and perform the duties of engineer soldiers.

The use of this kind of force was fully appreciated by him, an 1 on more than one occasion proved of great service to liim.

It is mentioned, that in 1547, the emperor found himself in the presence of the enemy, who were twice his strength in numbers, but who made the mistake of not attacking at once. Charles V. immediately began to intrench his army, and, by morning of the foUowinc day, was capable of repulsing the enemy. He con tinner to strengthen his position for twelve days. On the thirteenth iav, he received re-inforcements and moved against the enemy.

It is gifted, that Peter the Great, at the battle of Pultowa, vrhich terminated in the total defeat of the Swedish 'irmv, owed his success to intrenchmenta which he had had the foresight to construct in front of his line of battle, upon the night before the action.

The simple redoubt in the pass near Montenotte, defended by Colonel Rampon, in 1796, enabled Bonaparte to execute the details of a campaign unparalleled in the records of military history. Relative to this re

INTRODUCTION. 3

doubt and its defence, Thiers says, " It saved the general's plans, and perhaps, the future of the campaign."

Intrenchments played an important part in the late war in the United States.

In the beginning of this war, (1861), the sentiment or general opinion of the American volunteers was ftdrerso to intrenchments. The manual labor requisite for the construction of intrenchments was regjirded by them as degrading; their idea was '^a fair stand-up fight," in the open field. They applied the term ** dirt-diggers" to the advocates of intrenchments, and considered ^^ masked batteries" as devices unbecoming a civilized people.

Experience in war, and great necessity soon drove such erroneous views from their minds, and before the war ended, these same soldiers threw up intrenchments whenever the army halted, of their own free will and accord.

A writer stated, on this subject, that "they waited neither for orders, nor deployment of skirmishers, nor formation of lines. * * * * The rule was that the troops should proceed with this work without waiting for orders."

Their good sense soon caused them to appreciate the value of both nataral and artificial aids in the defence, and to learn that the fate of a battle frequently depended upon some slight protection given to a line, a protection so slight in many cases as to be hardly

4 INTRODUCTION.

worthy of the name^ such as a few rails heaped to gether, a shallow trench, etc. The result was that the American soldier became an adept in intrenching himself on the field of battle.

The Confederates made great use of intrenchments, and by their aid inflicted great losses upon our troops.

General Orant crossed the Bapidan in May. 1864, and attacked the enemy in the Wilderness. His most desperate assaults were not successful in driving the confederates from their intrenchments. He was successful only by moving around the position.

The losses suffered by the Union army, under General Grant from the time he crossed the Bapidan until he reached the James river, — about one month, — were equal in numbers to the entire force opposed to him in the beginning, when he crossed the Bapidan ; and these losses were largely due to the fact that the confederates occupied " intrenched *' positions.

General Sherman bears testimony in many places to the influence of intrenchments. In speaking of the assaults made on the enemy's lines, at Kenesaw mountain, June 24, 1864, he says. ''The two assaults were made at the time and in the manner prescribed, ai\d both failed, costing us many valuable lives, * * * our aggregate loss being near three thousand men, while we inflicted little loss upon the enemy who lay behind his well formed breast- works."

The experience acquired in this war in the United

INTRODUCTION, 5

States proved the necessity and value of intrenchments, even when extemporized and constructed in the presence of an enemy. It also proved that a very slight intrenchmenty when manned, and with the approaches to it swept by artillery, was practically impregnable.

The cost of carrying a line of intrenchment is incidentally mentioned in one of the reports of Major General H. G. Wright, the present Chief of Engineers, United States Army, who commanded the Sixth Corps of the Army of the Potomac, in the attack upon Petersburgh, in April, 1865. He said that it "cost us, in killed and wounded, a number equal perhaps to that of the entire force of the enemy actually opposed to us. It was an attack of nearly two divisions against a picket line covered by a simple trench and parapet ; but had it been held by two ranks of good troops it is doubtful if it could have been carried even by an entire corps.*' His conclusion was that "a well intrenched line, defended by two ranks of infantry cannot be carried by a direct attack,*' unless there are favorable circumstances, which it is not necessary to mention here.

The recent war between Bussia and Turkey confirms the experience gained by us in our late war, and places the intrenching tool almost on a level with the musket.

Lieut. Greene in his report says, that General Skobeleff made his men carry the spades and shovels on their persons. He remarks^ relative to this intrench-

6 INTRODVCnON.

ing tool, "they were heavy (weighing over five pounds), they were uncomfortable, they were in every way inconvenient, but each man had learned by hard experience to feel that his individual life depended upon his musket and his spade— and he took good caro to lose neither the one nor the other."

The student, seeing the advantages accruing from intrenchments hastily constructed, can easily draw his conclusions as to the value of lines of fortifications when there is time to build them properly.

The famous lines of Torres Vedras, in Portugal eonstructed by Lord Wellington ; the line of works built around the city of Washington during the late war ; the line of works defending Nashville, Tennessee ; and others are interesting subjects of study, and show how a defeated, or an inferior army by their use is able to hold its ground, for more or less time, against a superior or victorious enemy.

Field fortifications have attained such great importance, owing to the long range, the precision, and the rapid fire of modern arms, that no soldier can afford to be without a knowledge of the great principles underlying this branch of military engineering. The remark of Frederick the Great, true in his day, is still true at the present time, viz : " Officers require different kinds of knowledge, but one of the principal is that of fortification.'^

FIELD FORTIFICATIONS.

Chapter I. General Principles And Definitions

1. Positions. — The terra, position, is applied oy military writers to any piece of ground which is, or may be, occupied by a body of troops for the purpose either of making or repelling an attack.

When the purpose is that of repelling an attack, the position is called a defensive one. The motives which lead a body of troops to occupy a defensive position may spring from several causes. The most prominent of these causes are small n ess of numbers, inferiority in arms, lack of experience in war, or similar differences, which, at the time, render the enemy superior in strength.

A defensive position is occupied principally for the purpose of neutralizing this temporary superiority of an enemy, and to give to the troops holding the position, the chances of making a successful resistance to any attack made to dislodge them.

2. Strong positions. — Positions are called strong. when they give to their defenders all the chances oi making a successful resistance against any sudden assault which may be made by an enemy.

When the natural features of a position are such, that the defenders can shelter themselves from the enemy's fire, and at the same time be free to pour a fire upon the enemy's columns as they approach, it is evident that the chances are decidedly in favor of a successful resistance by the defence, ana cue position is more or less a strong one. Positions are not equally strong, in consequence of the natural features of the ground in one case being less favorably disposed for shelter, than in another. Their strength may however be increased by artificial means, and so much so, in many cases, as to render them technically ^* strong " or impregnable.

3. Fortifications.— The artificial means used to give additional strength to a position are termed fortifications, from the verb, "to fortify" [fortiSy strong, and facere to make] derived from the Latin.

The skilful combination of these means, and their construction, constitute a branch of Military Engineering known as the ^* Art of fortification."

The object of the art of fortification is to locate and construct, upon positions selected for defence, such additional aids or helps, that the defenders can by

GENERAL PRmCIPLES AND DEFINITIONS. 9

thoir use remove partially, if not entirely, the disparity existing between them and their assailants.

The art of fortification may therefore be defined to be that branch of military engineering which has for its object the strengthening of positions selected for defence.

4. Classes of fortifications. — ^Fortifications are usually diyided into two general classes, viz. :

Permanent and Temporary.

That class of fortifications which is usually con strncted in times of peace for the purpose of strengths ning positions which may be of military importance in ^ase of a future war, is termed permanent. Fortifications of this class are built usually with great care, and of durable materials. They are expected to last for a considerable time, and are therefore comparatively per manent in their nature.

That class of fortifications which is usually built after war has been declared, and to strengthen positions which have suddenly acquired a military import- *tnce, is known as temporary. Fortifications of this class may in some cases become permanent, but ordinarily they are built in a comparatively short time, of materials which are near at hand and can be obtained quickly, and frequently by the labor of the troops. The positions strengthened by them are frequently of transitory importance and soon abandoned, and the materials used are oftentimes perishable in theii nature. The fortifications are in use, in many eases, but for a short time ; are wanting in durability ; and are therefore temporary in their nature.

6. Field fortifications. — The temporary fortifications constructed by the labor of the troops constitute the greater part of the fortifications of this class. The troops are said to be *'in the field" at this time, and the fortifications constructed by them are usually known as field fortifications.

The subject of this book is a general discussion of the principles used, and the kind of works employed, in fortifying a position in the field, by the labor of troops.

6. Kinds of field fortifications. — Fortifications constructed in the field iare of two general kinds, according to the time employed in their construction, viz : Hasty and Ordinary.

Hasty fortifications are those which must be built in the time intervening between the end of a march and the beginning of a battle. This time is a very few hours at most, and the fortifications must be finished usually in a single night, or they will be useless.

Ordinary fortifications are also constructed hurriedly, but there is time enough to practically finisli them according to the plans upon which they are laid out.

Hasty fortifications are the kind built, in many cases, in the actual presence of an enemy ; ordinar}

OBNERAL PRINCIPLES AND DEFINITIONS. 11

fortifications are those built before the enemy arrives npon the ground.

7. General principles of fortifications.—

Fortifications, whatever be their class, are merely pas 81 ve means of defence.

Certain general conditions must be satisfied by a defensive position, to enable an armed force occupying it to contend successfully against an assailant, superior either in numbers, discipline, or arms. These conditions must be favorable to the defence and unfavorable to the assailant ; and when they do not exist naturally in

the position, must be supplied by means of fortifications. These conditions for a position, and in consequence, for a fortification, may be briefly enumerated to be as follows:

1. A shelter must be provided to protect the defenders against the missiles of the assailant, and to screen them from his view.

2. The position should be so arranged that an assailant can not approach within cannon range and not be exposed to the fire of the defence.

3. If practicable, the position should be taken, and the shelter arranged, so that an approach of the enemy would be difficult, and the enemy's movements towards the position be greatly impeded.

4. The position and shelter should be arranged so that the defenders movements to defend the position should not be hindered or impeded in any way.

8. General method of complying vnXtk these conditions. — The first condition or principle named is usually satisfied by making an excavation, and heaping the mass of earth thus obtained, until it is high enough and thick enough to screen and protect the defenders.

The second is fulfilled ordinarily by clearing away the ground in front of the position, and within cannon range, of all trees, houses, enclosures, hedges, etc., which might be used by the enemy as a screen ; and by arranging the mass of earth used as a shelter, so that the defenders can fire over it, or through it, and sweep, with their fire,the ground over which the enemy must approach.

The third s observed by placing the fortification behind some natural obstruction, as a marsh,- a water-course, etc. If this is not practicable, it is fulfilled by placing obstacles in front of the fortification and arranging them so that they shall impede the assailant's approach, but not screen his movements, nor protect him from the fire of the defence.

The fourth is complied with by removing any obstructions which might be in the way of the free movements of the defence, and by making communications which can be used by the defenders in moving from one part of the position to another.

9. Active and passive defence. — The terms, active and passive, are used to designate the kind of resistance which is offered in the defence of a posi«

GENERAL PRINCIPLES AND DEFINITIONS. 13

don. If the defenders, seeing an opportune moment, should leave the position and attack the enemy without waiting to be attacked ; or if during the assault, ^^ey leave the position for the same purpose, the resistance made is termed an active defence.

If no attempt is made to leave the work to attack the enemy, the resistance offered is known as a passive defence.

An active defence can be made, as a rule, only by a force which is strong enough and numerous enough to leave the position and become an attacking force. A passive defence is usually the resort of a force which is decidedly inferior to the assailant ; or is the defence made when the object of the resistance is fully attained if the enemy fails in his assault.

An active defence requires that the third principle just mentioned should be modified. It requires that the arrangements, organized to impede an enemy's approach, should be made so as not to interfere with the free movements of the defenders.

10. Definitions. — The principal parts obtained in the construction of an eartbern shelter are the mass of earth which is heaped up, and the excavation from which it was taken.

When the excavation is between the mass of earth and the enemy, it is called a ditch ; if the mass of earth is between the excavation and the enemy, the excavation is then designated as a trench.

14 FISLD FORTIFICATIONS.

It will be seen that the trench is the simplest form of shelter^ and the most quickly made. It fails to fully satisfy the conditions just named, as will be hereafter shown.

11. The ground occupied by a fortification is called the site of the work ; and a plane tangent to this ground is called the plane of site.

The outline of a fortification as drawn upon the ground, or its projection upon a horizontal plane, is termed the trace. A section of the fortification made by a vertical plane passed perpendicularly to the principal or directing line of the trace, is called the profile.