PART IX.

BATTERIES, AND FORTIFICATION.

BATTERIES.

_A battery_, in respect to its profile, may be either elevated, half sunken, or sunken; and it is usually reveted with gabions, fascines, sand-bags, &c.

_An elevated battery_ has its whole parapet raised above the natural surface of the ground, and, to procure the mass of earth required, a ditch is usually dug directly in front of the parapet.

_A half-sunken battery_ has its interior space, or terreplein, sunk some inches below the natural surface, and its parapet is composed of the earth thus obtained, and of that taken from a narrow ditch in front.

_A sunken battery_ has the whole of the earth taken from the interior space to form the parapet; and it must therefore be lowered from 2 feet to 3 feet 6 inches, according to the height of the gun carriages to be used.

_The half-sunken battery_ is constructed the quickest, as the diggers can work both in front and rear, at the same time. In a sunken battery, the diggers are as much crowded as in an elevated one, but, since the mass of parapet to be raised is smaller, it may be completed in much less time.

_Casemates, or vaulted batteries_, are made bomb-proof, and the embrazures are cut through the revetment.

_Barbet batteries_ have no embrazures, the guns being placed on traversing platforms to enable them to fire over the parapet.

_A direct fire_ from a battery is when the line of fire is perpendicular to the parapet, and an _oblique fire_ when it is oblique. The direct fire being preferable, the battery should be placed parallel to the object against which the fire is to be directed.

_The line of fire_ is an imaginary line drawn through the centre of an embrazure, in the direction of the object against which a battery is constructed.

_Embrazures_ are openings cut through parapets, flanks of bastions, &c., for guns to fire through.

_The neck of the embrazure_ is the inward, or narrowest part of it.

_The mouth of the embrazure_ is the outward, or widest part of it.

_The sole of the embrazure_ is the bottom, or space, between the cheeks or sides.

_The sill_ is the front of the sole.

_The genouillere_ is that part of the parapet which is immediately beneath the embrazures.

_The merlon_ is the portion of the parapet contained between two embrazures.

_The following dimensions are requisite to be proof,_

_Against musketry._—3 feet when of earth. 6 inches ” stone. 12 inches ” fir. 5 inches ” oak. 9 inches ” brick.

_Against cannon._—4 feet, when of wood, or brick. 6 feet against 6-pounders, when of earth. 9 ” 9-pounders, ditto. 14 ” 12-pounders, ditto. 18 ” 18 & 24-pounders, ditto.

_Note._—A 6-pounder shot, with a charge of one pound, will penetrate a _mass of ice_ to the depth of 4½ feet, at the distance of twenty-one yards.

GENERAL DIMENSIONS OF AN ELEVATED GUN BATTERY,

_reveted with fascines_.

ft. in. Space from the centre of one embrazure to that of the next, without traverses 18 0 Ditto, with traverses 22 0 Slope of the interior revetment, per foot (one-fourth its height) — 3 Fall of the superior slope, ditto (one-twelfth, ditto) — 1 Interior width of embrazures, measured on the sill 2 0 Exterior ditto, measured on the sole, at 12 feet from the sill 7 0 Slope of the cheeks of embrazures at the neck, per foot, (one-sixth of their height) — 2 Ditto, at the mouth, per foot (one-fourth their height) — 3 Distance from the centre of an embrazure to the foot of the slope of an adjoining traverse 7 6 Distance from the centre of an embrazure to the foot of the slope of an adjoining epaulment 5 0 Height of the sill about 3 0

DIRECTIONS FOR TRACING A BATTERY.

Batteries at sieges are generally traced in the dusk of the evening.

_Detail of men, and tools required:_

_Tracers.—1 non-commissioned officer, and 2 privates._

_Tools.—1 ground-square. 1 measuring tape._

_1 white tracing-line. 2 ten-feet rods. 1 bundle of pickets. 1 mallet._

_Directions._—The tracing-pickets, and mallet, are carried in a sand-bag, and a few long pickets are necessary to mark the embrazures. A line should be stretched about 40 feet in the direction of the object against which the battery is to be erected; this will show _the line of fire_. By means of a ground-square, a line may be laid down at right angles to the former, touching the first placed picket. This will be the interior base line. Another line must be placed parallel to this, at a distance equal to the sum of the breadth of the base of the parapet, breadth of the berm (if any), and breadth of the slope of the ditch (viz., about 27 feet), which line will represent the reverse slope of the ditch. A picket is then driven in on the interior base line, where it is intended to have one extremity of the battery, and as many long pickets (18 feet apart), measuring from this end, as there are guns, which will mark the centre of the embrazures. Then one more picket, 18 feet distant from the last, will show the other extremity. For the embrazures, drive in a picket at the distance of one foot on each side of the centre of the embrazures, for the width of the neck. Set off, and drive in pickets 3 feet 6 inches on each side of, and perpendicular to the line of fire, for the width of the mouth.

WORKING PARTY; TOOLS; AND MATERIALS REQUIRED

_for each gun; mortar; traverse; or epaulment; in an elevated fascine battery_.

_2 sappers, with 6 assistants_, to revet the work.

_12 infantry_, to excavate the ditch, and form the parapet.

_9 pickaxes, 15 shovels, or spades, 14 fascines, 18 feet long, 1 bundle of 50 pickets to 6 fascines, 3 mauls, 3 rammers, 1 saw_ to every two guns, _1 hatchet_ per gun, _1 bill-hook, 1 field-service level, 1 six-feet rod, 1 bundle of matches_ to every three guns, _1 lantern_, do., 1 lb. _of candles_, do., _1 bundle of gads_ to each gun, _1 tape of 50 feet in length_ per battery.

A battery will seldom be completed in less than 24 hours, when executed by inexperienced workmen; but by those inured to hard labour, and with proper reliefs, in about 10 hours. In light soil, that can be easily dug without the aid of a pickaxe, a man can, in 8 hours, load from 19 to 20 cubic yards of earth on barrows. If a pickaxe be required, 2 men will do the same quantity of work. A man can wheel 20 cubic yards of earth per day to a distance of 30 yards on level ground, or 20 yards on a ramp. Twenty cubic yards of earth will fill 500 wheelbarrows. When near the surface, in soil requiring but little the use of the pickaxe, an excavation of 6 cubic yards in a day of 8 hours would be a fair task for a soldier, who in general is little accustomed to working with the pickaxe and shovel.

SHELTER FROM AN ENEMY’S FIRE.[36]

The following method of sheltering the workmen from the enemy’s fire was used with great success during the construction of the batteries. It was towards the end of the siege that Lieutenant Néandre received orders to construct a battery 130 paces from the counterscarp, the covered way being strongly occupied by the enemy. Foreseeing the difficulties that would occur, Lieutenant Néandre provided 120 common platform planks, and, when the gabions were in their places, arranged the planks outside them, in such a manner as to present an inclined plane, (one end of the plank being supported on the gabion, and the other end resting on the ground towards the enemy): the gabions were then half filled with earth, and the pickets driven in. At this moment the enemy threw some fire balls, and fired a few shot, all of which went over. Soon after, the workmen were assailed with a well-sustained fire of musketry; but, on the balls striking the epaulment, they ricocheted and passed over the workmen, so that not a single man was hit. The battery was finished in a few hours, when the planks were drawn in, and used for the platforms.

A portable framework might be rapidly made, and used instead of the gabions, to obtain immediate cover from musketry fire; and, for sapping, the framework, with the planks fixed thereon, might be readily moved on trucks, as a substitute for the present sap roller.

EPAULMENTS.

Batteries at sieges are generally secured on one flank at least, by a parapet called an epaulment, forming an obtuse angle with that of the battery. Their use is to secure the reverse of the terreplein from any flanking fire, and they are not in general made so thick as the parapet, being seldom subject to a direct fire.

ELEVATED SAND-BAG BATTERIES.

The base of the interior slope of a battery reveted with sand-bags is rather broader than that of one reveted with fascines, being about one-third the height of the parapet. _Bushel sand-bags_ are now the only kind in use, and _when filled are of the following dimensions_:

Length 20 inches, breadth 10 inches, depth 5 inches. Number required per gun,—for the interior revetment 262 Ditto Ditto for the cheeks 360 --- Total 622

_Sand-bags_ are laid _header_, and _stretcher_, as in masonry; the ends which are tied being always hid. As the sand-bags near the neck of the embrazure would be destroyed after a few hours’ firing, and constantly require repairing, gabions, or casks should be substituted for them.

_Howitzer batteries_ are similar to those for guns, except that the interior openings of the embrazures are 2 feet 6 inches, and the soles are raised, towards the front, about 10°, in order to cover the gunners as much as possible.

_Mortar batteries_ are constructed with the same dimensions as gun batteries (the parapet being generally 8 feet high, and from 18 to 22 feet thick), but, as they have not embrazures, the ditch of elevated batteries is made two feet deeper to obtain the requisite quantity of earth. A preference would in general be given to the sunken, or half-sunken profile for a mortar battery, on account of its requiring less time for its construction, and it being of no consequence whether the platforms are sunken, or otherwise. Mortars are placed at the distance of 15 feet from centre to centre of each other, where no traverses intervene; and the parapet has the same profile as a gun, or howitzer battery.

When fired at 45° they are placed 12 feet from the revetment. Ditto 30° ditto 13 ditto Ditto 20° ditto 21 ditto Ditto 15° ditto 30 ditto Ditto 10° ditto 40 ditto

HALF-SUNKEN BATTERIES.

The sill is about half its total height above the natural surface of the ground; the most convenient depth to which the terreplein may be sunk is 2 feet. The height of a sill for a travelling carriage will be 18 inches, and for a garrison carriage one foot above the natural level. The profile of the parapet is the same as in an elevated battery.

Number of sand-bags required for reveting one merlon 180 Ditto ditto for cheeks of embrazures 360 --- Total 540

In forming the epaulment of a half-sunken battery, the earth is taken from a ditch in front, six feet wide, and about five feet deep.

SUNKEN GUN BATTERIES.

The soles of the embrazures are on a level with the natural ground, therefore the terreplein is sunk a sufficient depth for the solid, and, the merlons are formed of the excavated earth. The height of the solid depends on the nature of gun carriage to be used. The first operation is to trace out the embrazures. The profile is the same as in the elevated battery. Should there be traverses, all the earth excavated from the interior will be required; if not, the overplus may be scattered in the rear.

RICOCHET BATTERIES.

_Ricochet firing_ is the art of projecting shot, or shell, with a certain velocity, and in such a direction as to ensure its striking the ground at any spot that may be required; afterwards making several grazes upon the earth, and destroying, or striking all that may oppose its progress. The piece of ordnance is loaded with a diminished charge of powder, and the elevation is from 3° to 10°, which causes the shot to bound or hop along the ground. The smaller the angle under which the shot is made to ricochet, the longer it will preserve its force, and have effect, as it will sink in the same proportion so much less into the ground on which it bounds. In the ricochet of a fortress, or field work, the elevation should seldom exceed 10° to throw the shot over the crest of the parapet; but in the field, the objects to be fired at being principally infantry, and cavalry, the guns need seldom be elevated above 3°; as, under greater angles, the shot would be apt to bound too high, thereby defeating its intended purpose.

_Ricochet batteries_ should, if possible, be at a distance of 400 yards, or not exceeding 600 yards; as, from the uncertainty of the fire at a greater distance, at least two-thirds of the ammunition might be expended without producing any good effect.

_The best elevation to enfilade a work_ being from 6° to 9° measured above the parapet, the charge should be regulated accordingly, which varies from one-half, to one-tenth the service charge.

_Ricochet firing_ is very efficacious in dismounting the guns on the faces, or flanks of bastions, &c., the batteries for this purpose being erected on the prolongation of these works, and as nearly as possible perpendicular thereto, by which their whole length will be exposed to the effects of plunging, and destructive ricochet fire.

_Vide Tables of Ricochet practice_, pages 73, 79, 80.

FASCINES.

_Fascines_ are bundles of wood of various lengths, according to the purposes to which they are to be applied.

_Fascines_ for a revetment should be strong, and well bound. When small brushwood is used, _they are made 6 feet long, and 7 inches in diameter_, and are firmly bound with four or five withes, or gads.

_The gads_ are made of tough twigs, first twisted until the fibres separate, the smaller end is then turned round, so as to form a loop, or noose. To make a fascine 6 feet long, the workmen set up three fascine horses on the same level, and in a right line.

(_A fascine horse_ is formed with two pickets, each 5 feet long, driven about 1 foot obliquely into the ground, so as to cross each other at right angles 2 feet above the surface of the earth; and they are fastened together at their point of meeting, with cord, three or four-thread spun yarn, or gads.) The brushwood, stripped of all its leaves and smaller branches, and which should be from half to one inch in diameter, and 5 or 6 feet long, is then laid on the fascine horses, the thick ends being placed alternately at each end. The large stuff must be used to form the exterior, and the smaller twigs the interior of the fascine. Before binding the fascine, it must be compressed with a _fascine choaker_, which consists of a cord, or chain, equal in length to one and a half times the circumference of the fascine, fastened at one end to a lever 5 feet long and 2½ inches in diameter, with a loop at the other end, into which, after passing the chain round the fascine near the part to be bound, a lever, similar to the one already described, is inserted, and the brushwood is squeezed tightly together until the gad is tied. The fascine must be compressed in a similar manner before each gad is fastened. _The weight of the fascine_ is about 33 lb. _Three men can make a 6 feet fascine in twenty minutes._ Two of the workmen place the brushwood, while the third prepares the gads. If large brushwood can be procured, the fascines should be 18 feet long, the strength of the revetment being materially increased by diminishing the number of joints. _When the fascines are 18 feet long_, they are made nine inches in diameter, and the gads are placed 18 inches apart, the fascine horses being one yard apart. _This fascine weighs_ about 2 cwt. _Four men can make an 18 feet fascine in two hours_, or, if the wood be cut and brought to them, they can make four fascines in that time. _They require 3 bill-hooks, 1 saw, 1 fascine choaker (each lever about 6 feet long), and 6 fascine horses._ Three men prepare the brushwood, and lay it on the horses, while the fourth makes the gads.

The revetment is formed in proportion as the parapet is raised, the first fascine being half buried in the banquette, with three pickets driven vertically through it, each picket being from 3 to 4 feet long, and from 1¼ to 1½ inches in diameter at the thickest end. The second row of fascines is then laid a little in front of the first, so as to form the required slope, and three pickets are driven through each fascine; the extreme pickets through the fascine previously laid in the direction of the slope, the other perpendicular to the slope.

_The joints of the different rows of fascines_ should be so broken, that no two adjoining joints may be in the same line, and the ends of the fascines at the angles should alternately be flush with, and be inserted in the parapet; care being taken to lay the fascines so that the ties of the gads may be concealed in the parapets. Six rows of large fascines are sufficient to form the revetment of a parapet, the upper row being covered with a layer of sods, the grass upwards. When fascines of seven inches in diameter are used, eight rows are required.

GABIONS.

_Gabions_ are cylindrical baskets open at both ends, and are very commonly used to revet parapets. For the interior of parapets they should be _3 feet in height, and diameter_. _The common gabions are 2 feet in diameter, and 2 feet 9 inches high._

_To make them._—A directing circle consisting of two hoops, kept apart by bits of wood, to which both the hoops are secured with packthread, is first made. The diameter of the hoops must be such as to permit of the pickets for the gabion being driven between the exterior of the one, and the interior of the other. The directing circle is then laid on a level piece of ground, and from seven to twelve pickets are driven at equal distances apart, between the hoops; the number of pickets depending on the size of the rods, or brushwood with which the basket-work is to be made. The circle is then raised, and fastened to the middle of the pickets, and the web is made above it, two or three rods being used at the same time; the workman twisting them round each other while he interlaces them with the pickets, striking down the web from time to time with a stick. The _randing_, or _basket-work_, is continued to near the top of the pickets, where it is secured with four gads, each one passed round one of the pickets and four or five of the rods, which should be from 8 to 10 feet long, and not more than half an inch in diameter. The gabion is then pulled up, the finished end is placed on the ground, and the directing circle being removed, the remainder of the web is completed and secured as before described.

_Two men can make a gabion_ in three quarters of an hour, using about 80 rods for each gabion.

In forming the revetment, the gabions are placed touching each other with a slope of one quarter the height; the first row is surmounted with two rows of fascines side by side, and a second row of gabions rests on them.

SOD, OR TURF.

A revetment is sometimes made with sods of unequal sizes, called _headers_, and _stretchers_.

_The headers are 1 foot 6 inches long, 1 foot wide, and about 4½ inches thick._

_The stretchers are 1 foot wide, and long, and about 4½ inches thick._

Sometimes the sods are first cut all of the same dimensions—viz., 1½ foot long and 1 foot wide; this sod is then cut diagonally, across, so as to form two, and they are then all laid as headers. This saves nearly half the turf, and labour. The sods should be cut from good meadow land, previously mown, and watered; but the sods should not be laid or built when wet, because they would shrink in dry weather, and all the joints would open. The sod-work is laid with the grass downwards, either alternately headers, and stretchers, or two stretchers to one header; care being taken that the joints of no two rows fall immediately over one another, which is termed breaking joint. If the layers of sods are laid perpendicular to the slope, they will answer better than if laid horizontally. Each sod should have two or three pegs driven through it, to secure it to the work beneath. When the revetment is completed, the whole should be cut off smooth to the proper slope; a pair of hedge-clippers, or a cutting knife, will answer well for this purpose.

_One man can lay 19 square yards of sod-work in eight hours_, when the sods are brought to the spot, and require no previous trimming.

PLATFORMS.

To facilitate the working of a gun, it must be placed on a platform of stone, or timber and plank: but, as a temporary measure, when required to fire only in one direction, timbers to take the wheels will suffice. The usual inclination given to platforms, from the rear to the front, is half an inch per foot. Platforms on barbettes should be perfectly level, and their dimensions must depend on the extent of the lateral range which may be required.

_In laying a gun platform_, the first thing to be done is to fix the _hurter_, which may be a piece of timber 7 or 8 feet long, and 7 inches square, or a strong fascine 9 feet in length may be advantageously used. The hurter is intended to take the wheels, or trucks of the carriage when the gun is run out, and to prevent their damaging the interior slope of the parapet. The position of the hurter necessarily depends therefore on the steepness of the interior slope. The hurter should be placed perpendicular to the axis, or central line of the embrazure. Three, four, or five sleepers of from 6 to 8 inches square, are then laid, their upper surface on a level with the bottom of the hurter, and they are covered with two-inch planks, nailed down when three sleepers are used; but if there be four or five sleepers, the planks may be confined by two _ribbands_ (which are pieces of wood of the same length, but weaker scantling than the sleepers) and the platform racked down with _rack lashings_ at the proper intervals.

_A rack lashing_ consists of a piece of 2-inch rope about 9 feet long, which is fastened to a stick 15 inches long, 2 inches wide at the head, with a hole in it to receive the lashing, and tapering to a blunt point: it is passed round the timber, and sleeper beneath, then twice round itself. The end of the stick is then put into the loose gromet so formed, and twisted round until the whole is firmly secured, when the stick is turned flat on the upper piece of scantling.

The gun, and mortar platforms for sieges are now made rectangular: the dimensions of the former are 15 feet long by 10 feet 6 inches broad; those of a mortar platform are 7 feet 6 inches long by 6 feet 6 inches broad. Mortar platforms are laid exactly horizontal, the front part being placed 5 feet within the foot of the interior slope of the parapet.

_Madras platforms_ consist of two stout planks about 12 feet long; they are supported on two sleepers, having a transom in front. The planks are secured with a moveable bolt, or pivot to the front transom, slide freely on the sleepers, and are connected together in rear by two cross pieces parallel to the rear sleeper, one in front, and the other in rear of it. To the centre of these two cross pieces is bolted another 12-feet plank, called the trail-piece, of a width equal to the distance between the cheeks of a siege-carriage, which is supported on a sleeper in the rear. When the gun is to be traversed, the whole platform is moved on the sleepers on the pivots in front. These platforms are chiefly intended for a direct fire. Two wedges are required for this platform to form inclined planes for the wheels, in running the gun on, or off the platform. Each wedge is of elm, 3 inches thick, 2½ feet long, and 1 foot wide, with a block to give the requisite height, the block being 12 inches long, 4 thick, and 7 in extreme height.

_Alderson’s platform._

The platform invented by Colonel Alderson, R.E., is 15 feet long, by 9 feet wide; and is composed of 46 similar pieces of timber (baulks) each measuring 9 feet × 5 inches × 3½ inches. Of these, ten are used as sleepers, and the remainder as planking. The weight of the platform (when 15 feet long and 9 feet wide) for guns is 15 cwt. 2 qrs. 14 lb. By addition of the small beams, this platform may easily be extended from 15 to 18 feet.

_Dimensions, and weight of Platforms, for Guns, &c._

+--------------------------+----+--------+--------+--------+-----------+ | Nature of Platform, and |Num-| | | Thick- | | | articles required. |ber.| Length.|Breadth.| ness. | Weight. | +--------------------------+----+--------+--------+--------+-----------+ | | | ft. in.| ft. in.| ft. in.|cwt.qr. lb.| | GUN, AND HOWITZER. | | | | | | | Sleepers | 5 | 15 | 5 | 5 | 4 2 1 | | Planks | 20 | 10 6 | 9 | 2 | 7 3 22 | | Ribbands | 2 | 15 | 4 | 4 | 1 0 18 | | Rack-sticks, and lashings| | | | | 10 | | | | | | |-----------| | _Total weight_ | | | | | 13 2 23 | | | | | | |-----------| | MORTAR. | | | | | | |_Covered with oak planks._| | | | | | | Sleepers | 7 | 7 6 | 6 | 6 | 3 3 7 | | Planks | 10 | 6 6 | 9 | 3 | 5 1 22 | | Ribbands | 2 | 7 6 | 4 | 4 | 2 10 | | Rack-sticks | 10 | 1 3 | | | 15 | | | | | | |-----------| | _Total weight_ | | | | | 9 3 26 | | | | | | |-----------| | _Made entirely of fir._| | | | | | | Sleepers | 7 | 7 6 | 6 | 6 | 3 3 7 | | Planks | 8 | 6 6 | 11¼ | 4 | 4 2 18 | | Ribbands | 2 | 7 6 | 4 | 4 | 2 10 | | Rack-sticks | 8 | | | | 12 | | | | | | |-----------| | _Total weight_ | | | | | 9 0 19 | | | | | | |-----------| | MADRAS. | | | | | | | _Wood work._ | | | | | | | Side-pieces | 2 | 12 6 | 1 0 | 4 | 3 0 18 | | Trail-piece | 1 | 12 | 1 4 | 4 | 1 1 3 | | Fore transom | 1 | 7 | 6 | 6 | 2 19 | | Hind transoms | 2 | 6 6 | 9 | 3 | 2 20 | | Sleepers | 3 | 9 | 6 | 6 | 2 0 16 | | Wedges | 2 | | | | 2 7 | | | | | | | | | _Iron work._ | | | | | | | Long bolts, ⅞in. diameter| 2 | 11½ | | | 6 | | Short bolts, ditto | 6 | 7½ | | | 11 | | | | | | |-----------| | _Total weight_ | | | | | 8 2 16 | +--------------------------+----+--------+--------+--------+-----------+

GUN, AND HOWITZER PLATFORM.

_For carrying this platform_, two men are required for each sleeper; one man for each plank, and ribband. The non-commissioned officer carries the rack-sticks.

_A platform may be laid down_ in an hour by expert men, and may be dismantled in three minutes.

MORTAR PLATFORM.

_Detailed as above._ One non-commissioned officer, and seventeen men carry the platform. _Time required for laying down, and dismantling_, similar to the above.

MADRAS PLATFORM.

_In an elevated battery, the platform may be laid down_ by expert men in half an hour, _and may be dismantled_ in three minutes.

BREACH.

_The best place for making a breach_, in ravelins, bastions, &c., is about thirty yards from their salient angles. The batteries should commence by marking out by their fire the extent of the breach intended to be made, first by striking out a horizontal line as near the bottom of the revetment as possible, and afterwards two others perpendicular to, and at the extremities of this line. Should the breach be required to be extensive, it will be necessary to form intermediate lines. Then, by continuing to deepen these two or more cuts, and occasionally firing salvoes at the part to be brought down, the wall will give way in a mass. The guns must, however, at first fire low, and gradually advance upwards until the breach is effected; and when the wall has given way, the firing should be continued until the slope of the breach is made practicable.

TO BURST OPEN GATES OF FORTRESSES, ETC.

A leathern bag, containing about 50 lb. of powder, should be hooked upon the gate, as near the centre as possible (or be laid on the ground, close to the bottom of the gate, and tamped with sods, &c.), and be fired by means of a piece of portfire, or match, passed through a hole in the bottom of the bag.

FORTIFICATION.

_Offensive fortification_ is the art of conducting a siege.

_Defensive fortification_ comprehends military architecture, and is the art of securing, or protecting a place by works, to resist a siege.

_Natural fortification_ consists of obstacles, such as marshes, mountain passes, &c., which are found in some countries, and should be taken advantage of to impede the approaches of an enemy.

_Artificial fortification_ comprises those works which are constructed to defend a place.

_Permanent fortification_ is the art of putting towns, &c., into such a state as at all times to be prepared to resist the attack of an enemy.

_Field fortification_ is the method of fortifying a camp, or position, buildings, &c., and it includes the construction of redoubts, entrenchments, &c. Works of this nature are considered as temporary.

_Irregular fortification_ is the art of fortifying a place of an irregular figure, situated where the country does not admit of giving to the several works their due proportion according to rule.

_A Command_ is the vertical elevation of one work above another, or above the country.

_A Command in front_ is when an eminence is directly facing the work which it commands.

_A Command in the rear_, or reverse, is when any eminence is directly behind the work which it commands.

_A Command by enfilade_ is when an eminence is situated in the prolongation of any line of a work, and a considerable part of it may be seen from thence; this line will be subject to enfilade, and such a command is the most dangerous.

_The Rampart_ (A T R) is an elevation of earth, obtained from the excavation of the ditch; and is that part of the fortification which is situated between the ditch, and the town, consisting of an interior slope, terreplein, banquette, parapet, and exterior slope or escarp.—(_Vide Plate._)

_The Interior slope_ (A) is the inclination of earth nearest to the town.

_The Terreplein_ (T) is the upper part of the rampart, which remains after having constructed the parapet.

_The Parapet_ (R) is a mass of earth elevated on the terreplein of the rampart, on the side towards the country; being from 18 to 22 feet thick, and from 6 to 8 feet high. The top is formed with a slight declivity towards the country, which is called the _superior slope_.

_The Banquette_ is an elevation of earth, or step, on which the soldiers stand to fire over the parapet.

_The Revetment_ is the masonry which retains the earth of the rampart on its exterior side. It is about 5 feet thick at the top, and its slope is one-fifth, or one-sixth its height.

_The Berm_ is a space, or path, sometimes left between the exterior slope of the rampart, and the ditch. It serves as a communication round the works, and prevents the earth falling into the ditch.

_The Tablette_ is a flat coping-stone, on the exterior of the top of the escarp of whole revetment.

_The Cordon_ is a semicircular projection of stone, whose diameter is about one foot, placed at the top of the slope of the revetment of the escarp.

_The Escarp_ (a) is the exterior slope, or wall of the rampart.

_The Counterscarp_ (b) is the wall, or slope of the ditch, opposite to the escarp.

_The Faces_ of a work (p q) are those parts which form a salient angle, projecting towards the country.

_The Flank_ (q G) is the part of a work so disposed as to defend another; joining the face of a bastion to the curtain, &c.

_The Bastion_ (M L) is a work composed of two faces, and two flanks. Bastions are joined by curtains, and are constructed salient, and with flanks, in order that the whole escarp may be seen, and that a reciprocal defence may be obtained.

_Bastions are of various kinds_—viz., full (M), empty (L), also flat, detached, demi, and tower bastions.

_A Full bastion_ (M) is when the terreplein occupies all the interior space of the bastion. From the description of this bastion, that of all the others may be ascertained.

_The Curtain_ (G R H) is that part of the rampart which lies between two bastions, and joins the flanks thereof.

_A Front of fortification_ consists of two half bastions, and a curtain.

_The Ditch_ (B) is an excavation from 12 to 24 feet deep, and from 90 to 150 feet broad, surrounding the rampart. The side of the ditch nearest the place forms the escarp (a); and the opposite part, the counterscarp (b) is made circular opposite to the salient angles of the works.

_The Covered way_ (V) is a space of about 30 feet broad, extending round the counterscarp of the ditch, being covered by a parapet from 7 to 9 feet high, with a banquette.

_The Glacis_ (X) is the superior part of the parapet of the covered way, forming a gentle slope towards the country, and terminating at from 120 to 180 feet; it covers the revetment of the body of the place.

_The Places of arms_ of the covered way are spaces contrived in the salient, and re-entering angles of it; those (c) in the re-entering angles flank the branches of it, and contain troops for sallies, and its defence; and those (P) in the salient angles serve for assembling the Troops destined for the defence of the covered way.

_The Sally-ports_ are openings cut in the glacis, at the faces of the re-entering places of arms, and at the branches of the covered way. They are used in making sallies from the covered way.

_The Traverses_ (n) in the covered way, are parapets which cross the breadth of it at the salient, and re-entering places of arms, &c. They cover the troops who are drawn up behind the parapet of the covered way, from the enfilade fire of the enemy. There are passages cut in the parapet of the covered way, close to the traverses, in order to form a communication from one part of the covered way to another: these passages are about 6 feet wide, and are provided with gates.

_A Citadel_ is a fortress joined to the works of a place, and is fortified both towards the town, and country. It should always be situated on the most commanding ground, serving to keep the inhabitants in awe, and, should the town be taken, it becomes a retreat for the garrison.

_The Esplanade_ is a space of even ground, clear of buildings, situated between the town, and citadel.

_The Body of the place_ (or _Enceinte_) consists of the works next to, and surrounding the town, in the form of a polygon, whether regular, or irregular.

_Outworks_ are those works which are constructed beyond the body of the place, such as tenailles, ravelins, &c.

_The Tenaille_ (D) consists of two faces, and a small curtain. It is constructed between the flanks of the bastions in front of the curtain, and has a terreplein, parapet, and banquette.

_The Ravelin_ (P) is constructed opposite the curtain, (in front of the tenaille,) is composed of two faces, which form a salient angle towards the country, and of two demi-gorges formed by the counterscarp.

_A Horn-work_ is composed of two half bastions, and a curtain, with two long sides directed upon the faces of the bastions, or ravelins, so as to be defended from them.

_A Crown-work_ is composed of a bastion between two curtains, which are terminated by half bastions. It is joined to the body of the place by two long sides.

_Lunettes_, and _Tenaillons_ are works constructed on each side of ravelins, consisting of two faces.

_A Flèche, or Arrow_, is constructed along the foot of the glacis before the re-entering, and salient places of arms. It consists of a parapet, whose faces form a salient angle, and are about 120 feet long, and it has a communication with the covered way, cut through the glacis.

_The Caponiere_ (Y) is a work intended to cover a passage across the ditch. That from the tenaille to the gorge of the ravelin is a road about 30 feet wide, covered on each side by a parapet 7½ feet high, its superior slope terminating in a glacis about 60 feet wide.

_A Cunette_ is a small ditch made in the middle of a dry ditch, to drain off the water from the place, &c.

_A Batardeau_ (e) is a solid piece of masonry, 7 or 8 feet thick, crossing the whole breadth of the ditch opposite the flanked angles of the bastions. It retains the water in those parts of the ditch which require to be inundated.

_A Ramp_ (t) is a road cut in the interior slope of the rampart, forming a communication from the town, &c., to the terreplein.

_A Cavalier_ is a work constructed upon the terreplein of a full bastion, being from 8 to 12 feet above the rampart, with a parapet 6 feet high. Its use is to command some rising ground within cannon-shot, and to serve as a traverse for preventing the neighbouring curtains from being enfiladed.

_Parallels, or Places of arms_, thrown up at sieges, are trenches formed to connect together the several approaches to a besieged place.

_Zig-zags, or Boyeaux of communication_, are trenches made for the approaches from the parallels to the besieged place. They are generally 3 feet deep, and have a parapet, and banquette.

_A Redan_ consists of two faces forming a salient angle (which should not be less than 60°) with parapet, &c.[37]

_A Lunette_ has two faces, similar to the redan, and also two flanks.[37]

_A Redoubt_ is a square, polygonal, or circular field fort.[37]

_A Star fort_ consists of a succession of salient, and re-entering angles, formed on the sides of a polygon. These forts are usually constructed on a triangle (when they have six salient points), or a square (having eight salient points).[37]

_Têtes de pont, or Bridge heads_, consist of redans, &c., which are constructed upon the banks of rivers, to protect the passage across them.[37]

_Lines_ are formed for the entrenchment of armies, and are composed of a succession of redans, &c., joined by curtains, which should not be more than 120 yards distant from each other, to afford mutual protection, and defence.[37]

_An Epaulment_ is an elevation of earth thrown up to cover troops from a flanking fire.

_Loop-holes_ are oblong holes, from 15 to 18 inches long, 6 inches wide within, and 2 or 3 without. They are cut through timber, or masonry, for the services of small arms.

_Palisades_ are stakes of strong wood, 8 or 9 feet long, and 6 inches thick, fixed about 3 feet in the ground, and 3 or 4 inches asunder.

_Fraises_ are a kind of palisades, placed horizontally, or obliquely in the exterior slope of ramparts.

_Chevaux de frise_ consist of a piece of timber from 9 to 12 feet long, and about six inches in diameter, into which staves are inserted cross-ways, about 9 inches asunder, about 2 inches thick, 6 feet long, and pointed at the end, if not shod with iron. Their use is to stop up a breach, defend a passage, or form an entrenchment against cavalry. Chevaux de frise are sometimes made entirely of iron.

_Abattis_ consist of trees with their branches shortened, and sharpened at the ends; they are used instead of chevaux de frise on an emergency.

_Hurdles_ are about 3 feet high, and 2 broad, and are used in sieges to stop up breaches, &c.

_Trous de loup_ are holes dug in the ground in the form of an inverted cone, about 6 feet deep, and 4½ in diameter at the top, having a picket fixed in the centre of the bottom, 6 feet long, and 4 or 6 inches square, the point being on a level with the upper surface of the ground. These pits are used to prevent the approach of bodies of cavalry.

PERMANENT FORTIFICATION.

_Remarks, and general rules._

The ground plan, and relief of bastioned fortifications are mutually dependent on each other; and, as a variety of causes occur to influence both according to the various sites occupied, it is impossible to give them any fixed arrangement, and dimensions, applicable under all circumstances. However, under the supposition that the site to be fortified is a horizontal plane, a great number, and variety of systems have been proposed at different times; almost every author, who has treated of fortification, having invented one, at least, of his own. Notwithstanding this diversity of opinion, as to the best system, all agree that the following general principles should not be lost sight of in the construction of fortifications.

1. Salient angles should be as large as possible, and never less than 60°. The larger they are the smaller will be the space in front undefended by direct fire. If less than 60°, the salients of earth are too acute to stand firmly for any length of time; and the angles of masonry are easily damaged; besides which the space within the parapets becomes too restricted to admit of a gun being worked near the angle.

2. Angles of defence should be right angles, or slightly obtuse. If less than right angles, the fire from the flanking works might injure the defenders of the works they flank; as troops generally, and more particularly at night, fire in a direction perpendicular to the parapet; and if too obtuse the fire might be directed wide of its object. Besides, embrazures should be cut as direct as possible; as the more they are oblique, the more they weaken the parapet.

3. The length of the lines of defence shall be such, that the works defended may be within the effective range of the projectiles used.

4. The works should be so disposed that the assailants may not be able to obtain cover in any part of the exterior, within range of the projectiles of the defenders.

5. The escarps of the body of the place should be of such height, or construction, as to be secure against escalade.

6. The masonry should be sufficiently covered from the view of the enemy, to prevent his making a practicable breach from a distance.

7. The interior of every work should be completely covered from the view of an enemy outside it; so that he may not be able to fire directly into any part of it. Interior works should therefore have a command over those in front of them, at least equal to the height which a besieger can give to the parapets of his lodgments, and which is seldom less than 3 feet.

8. Every opportunity should be seized of so directing the faces of works that an enemy may not have it in his power to enfilade them by ricochet fire.

9. In the general construction of fortifications the salients should be few, and sufficiently prominent to force the besieger to take them before he can attack the re-entering parts. The object of this is to reduce the number of points of attack, as, the fewer they are, the less advantage an assailant derives from his numerical superiority.

10. Permanent fortifications must be considered very incomplete without a sufficiency of casemated cover for the sick, and wounded, and for the portion of the garrison off duty. The magazines of ammunition and provisions, should also be secure from the effects of shells; and the supply of water ample, and certain.

11. Small enclosed works, in which the defenders must be crowded, without cover from vertical fire, should never be employed in permanent fortification. The strength they impart can never make up for the loss the garrison must suffer by them.

12. Outworks, and detached works should have easy communications with the main work, to admit of their garrisons receiving reinforcements, or supplies, when necessary; and to enable them to retreat, when the works are no longer tenable.

13. Every enclosed defensive work of importance should, if possible, be provided with a keep, or citadel, or interior retrenchment, to which the garrison may retire when the main enclosure (or enceinte) is forced.

14. Outworks, and detached works near the body of the place, should be so constructed that the enemy, when he has taken them, may not be able to use them as defensive works.

15. Outworks, and detached works, should always be of sufficient strength to force the enemy to make _regular_ attacks on them. Advanced works of a weak construction are likely to do more harm than good; for the troops of the garrison seeing them taken with comparative facility, would naturally lose confidence in the strength of their remaining defences, while that of the assailants would be increased by early success.

16. All fortifications should be provided with means of egress, and ingress, to enable the garrison to assume the offensive, whenever opportunities offer; and to admit reinforcements into the fortress.

17. There are very few fortified places that agree with any published system, though some resemble one or other of the systems, or consist of combinations, or modifications of them. The systems which have been wholly, or partly carried into execution are, of course, the most interesting, and form valuable subjects of study. A knowledge of their advantages, and defects, and the best methods of attacking, and defending them, will enable the military student properly to appreciate works which have been, or are to be constructed; and the operations by which fortresses have been, or may be captured.

VAUBAN’S FIRST SYSTEM.[38]

_To describe three Fronts of fortification, on a hexagon._—_Vide Plate._

With a radius of 360 yards, the length of the exterior side of the fortification (taken from a scale of equal parts), describe a semicircle, which divide into three equal parts, and draw lines to the points of division; thus forming _three exterior sides_. Bisect each of these by perpendiculars drawn to the centre of the polygon, on which set off ⅙th of the exterior side, (if a hexagon,)[39] through which points draw _the Lines of defence_; on these set off 2/7ths of the exterior side, from the angles of the circumference, for the length of the faces of the bastions; with radius of the distance between the two faces describe arcs joining the lines of defence, and draw the cord of these arcs for _the flanks of the bastions_; a line joining the interior extremities of the flanks will give the length of _the curtains_.

_Or, to describe one Front of fortification._

For the exterior side, draw a line 360 yards in length, at the ends of which, lines are to be directed to the centre of the polygon, at the angle required; (_vide_ PRACTICAL GEOMETRY—_To find the angles at the centre, and circumference of a regular polygon_,) then bisect the exterior side, and draw the perpendicular, &c., &c., as described for the construction on a hexagon.

[Illustration: Vauban’s 1^{st} System.

_J. W. Lowry, sc._]

_Main ditch._

From the salient angles of the bastions, with 38 yards as a radius, describe arcs, to which draw tangents, directed to the angles of the shoulders of the bastions.

_The Tenaille._

Draw lines parallel to the lines of defence, at the distance of 16 yards, for the faces of the work; its flanks, and curtain are constructed parallel to the flanks of the bastions, and curtain, at the distance of 11 yards.

_The Ravelin._

From the re-entering angle of the counterscarp, make the capital of the ravelin 80 yards in length, and from its summit draw lines to points, on the faces of the bastions, 11 yards from the angle of the shoulder; the junction of these lines, and the counterscarp of the main ditch will determine the length of the faces of the ravelin. The gorge is formed by drawing lines 24 yards from the re-entering angle of the counterscarp to the intersection of the perpendicular, and the exterior side. From the salient angle of the ravelin, with a radius of 24 yards, describe an arc, to which draw tangents parallel to the faces, for the breadth of the ditch.

From the outline of the works draw the following parallels inwards:—

_Rampart._

1. At the distance of 6 yards, for the thickness of the parapet.

2. From which 12 yards, for the breadth of the terreplein.

3. From which 6 yards, for the breadth of the interior slope.

_Tenaille._

Draw lines parallel to the faces, at the distance of 6 yards, for the parapet.

_Ravelin._

To the faces of the work draw the following parallels:—

1. At the distance of 6 yards, for the parapet.

2. From which 8 yards, for the terreplein.

3. From which 5 yards, for the interior slope.

_Covered way._

Draw lines parallel to the counterscarp, at the distance of 11 yards, for the breadth of the covered way.

_Salient places of arms._

These are formed by the salients of the branches of the covered way.

_Re-entering places of arms._

Set off 40 yards on each side of the re-entering angle of the counterscarp for their demi-gorges, from which points draw their faces at an angle of 100 degrees.

_Glacis._

For its breadth, draw parallels to the branches of the covered way, and the re-entering places of arms, at the distance of 50 yards.

_Traverses._

Those at the re-entering places of arms are erected perpendicular to the covered way; those at the salient places of arms are formed on the prolongation of the faces of the bastions, and ravelins, across the covered way; all the traverses are 6 yards thick at the top. The passages, cut out of the glacis, to enable the troops to pass round the traverses, are 4 yards wide.

_Ramps._

Flank of the empty bastion.—Set off 42 yards, from the angle of the flank of the interior slope, diagonally along the slope, for the length of the ramp, to which draw a parallel line 5 yards distant, for their breadth, which mark by a perpendicular, prolonging it, and setting off 6 yards for the interior slope; to which point, from the end of the ramp, draw a line; and also from the same point draw another line parallel to the side of the ramp, and joining the interior slope of the face of the bastion.

Flanked angle of the empty bastion.—From the angle of the interior slope set off 16 yards on each side, from which points draw lines 42 yards in length diagonally along the interior slope for the length of the ramps; to which draw parallels, 4 yards distant, for their breadth; erect perpendiculars from the points (16 yards from the angle) until they intersect each other, from which point as a centre, with radius of the distance between the ramps, describe an arc joining the head of the ramps of the two faces; concentric to which, with a radius 6 yards less than the former, describe another arc, to which draw tangents from the termination of the ramps, representing their slopes.

Gorge of the full bastion.—From the angle of the interior slope, set off 16 yards on each side, from which points draw lines 42 yards in length diagonally along the interior slope; draw parallels to these at the distance of 5 yards, for the breadth of the ramps; erect perpendiculars at their head, from the intersection of which as a centre, with radius of the distance between them, describe an arc, parallel to which, with radius 6 yards less, describe another arc, to which draw tangents, completing the interior slope of the ramps.

Ravelin.—From the angle of the interior slope, set off 12 yards on each side; from these points draw lines 30 yards in length, diagonally along the interior slope, for the length of the ramps; to which draw parallels 4 yards distant for their breadth; erect perpendiculars at the commencement of the ramps, and from their intersection, as a centre, with radius of the distance from the ramps, describe an arc joining the two ramps; also from the junction of the perpendiculars draw lines to the termination of the ramps, for their slopes.

_Caponniere._

Make the passage of this work 30 feet wide, including the banquette on each side; the superior slope of each parapet terminates at 20 yards’ distance.

_Bridges, and communications._

These are about 14 feet wide.

_Stairs, or Pas de souris._

These steps of masonry are made at the gorges of the several works, and at the salient, and re-entering angles of the counterscarp. Those at the salients are generally 24 feet long, and at the re-entering angles 30 feet; they are 5 feet wide, and their steps 1 foot distant from each other.

_Sally-ports._

These passages, cut through the glacis, are about 12 feet wide, and 18 feet long.

[Illustration: Profile of Vauban’s 1^{st} System.

_J. W. Lowry, sc._]

PROFILE, OR SECTION OF VAUBAN’S FIRST SYSTEM.

_Construction._

The interior slope of the rampart has a base of 18 feet, and a perpendicular height of 17 feet 6 inches.

The terreplein has a breadth of 25½ feet, its height being 18 feet sloping to 17 feet 6 inches, the height of the interior slope.

The banquette is 3 feet in height, the tread 4 feet wide, and the slope 5 feet wide.

The parapet is 4 feet 6 inches higher than the banquette, its interior slope is 18 inches, its thickness 18 feet, and its superior slope has a declivity of 3 feet; the revetment is 3 feet thick.

The escarp has a perpendicular height of 36 feet, measuring from the cordon to the bottom of the ditch.

The tablette, or coping-stone, at the top of the revetment, has a projection of 6 inches square.

The cordon is semicircular, its radius being 6 inches.

The slope of the escarp is 6 feet, the thickness of its revetment at the top 5 feet, and at the bottom 11 feet.

The counterfort joins the escarp; it is 1 foot lower than the top of it, 9 feet wide, and it extends to the bottom of the foundation, which is 3 feet below the bottom of the escarp; the retreat, or lessening, has a width of 1 foot.

The ditch is 38 yards wide, from the salient angle of the bastion.

The counterscarp is 17 feet 6 inches in perpendicular height, its slope being 3 feet, and its thickness at top 3 feet, the bottom, therefore, having a thickness of 6 feet; the foundation is 3 feet; and the retreat 1 foot.

The terreplein of the covered way is 20½ feet wide, and its slope is 6 inches. The banquette is 3 feet high, its tread 5 feet, and its slope 6 feet. The parapet is 4 feet 6 inches above the banquette, and its interior slope is 18 inches. The glacis, which forms the superior slope of the parapet of the covered way, is 50 yards in breadth.

The counterfort of the counterscarp is 5 feet in thickness, being 1 foot lower than the top of the counterscarp, and extending as low as the foundation of it.

The counterforts of the escarp, and counterscarp are 15 feet distant from centre to centre of each other, those of the escarp being at the end adjoining it 5 feet 6 inches, and at the termination 3 feet 8 inches thick; those of the counterscarp being in thickness at the larger part 3 feet 6 inches, and at the smaller 2 feet 4 inches.

_Vide Plate._

MODERN SYSTEM.

A Interior slope. T Terreplein of rampart. R Parapet of rampart. A T R Rampart. a a a a Escarp, or exterior slope of rampart. M Full bastion. L Empty bastion. p q Face of bastion. q G Flank of bastion. K o p q G Outline of bastion. G H Curtain. t Ramps. B Ditch. D Tenaille. Y Caponniere. e Batardeau. F F F Ravelin. S Redoubt in ravelin. b Counterscarp. n Traverses in covered way. c Re-entering places of arms. W Redoubt in ditto. P Salient places of arms. V Covered way. X Glacis.

[Illustration: FORTIFICATION.

Modern System.]

FIELD FORTIFICATION.

REMARKS, AND GENERAL RULES.

1. The size of a work depends in general upon the number of men who are to defend it. If labour is the sole object of attention, the advantage must necessarily be the greater in proportion as the size of the work is less; but if the accommodation of the troops is only to be considered, the advantage depends greatly upon occupying much ground.

2. The form of the work should be such as to contain the greatest surface with the least perimeter. By an adherence to this maxim, we obtain the greatest accommodation for the troops with the least labour. The form of a field work seldom depends upon choice, but generally upon the spot where it is to be raised, the purposes for which it is to be constructed, and the nature of the ground in the vicinity.

3. The interior of the work ought to be so covered by the parapet, that the men within, except when on the banquette, may not be seen from any part without, at the distance of cannon-shot.

4. The circumjacent ground (to as great a distance as possible) ought to be cleared, that the enemy may not conceal, or shelter himself against the fire from behind the parapet. The nearer to the work that the enemy can find cover, the more advantageously he can form his dispositions; and, as his attacks may consequently be made with greater vigour, and be more readily supported, the success will be the more probable.

5. The flanking parts ought to be sufficiently capacious to contain all the men required for the defence of the flanked portions of the work.

6. The flanking parts ought to have nearly a direct view of those flanked; that is, the defence should be nearly at right angles, the most advantageous angle being 100 degrees.

7. The parts flanked ought to be within musket fire of their flanking parts.

8. The fire ought to be equally distributed, that every part of the work may be equally defended.

9. The work ought to be equally strong in all its parts, that it may everywhere equally resist the assaults of the enemy; and the parapet should be thick enough to withstand the shot fired against it.

10. The dimensions of the parapet should not only be sufficient to secure, and cover the troops within the work, but ought also to be of such a form as to afford a full view of the enemy in his approach; and at the same time discover, as little as possible, the men employed for its defence.

_Capacity of Field works._

The perimeter of a work, and the number of men to defend it, should bear a just proportion to each other, one yard being allowed for each man, or for each file of men, according to the nature, and object of the work.

In calculating the area of enclosed field works, 10 square feet may generally be estimated for each man, and 324 square feet for each gun, and its stores.

_Content of Field works._

In square redoubts, or works having salient angles, if the areas of the sections of the parapet, and ditch, are made nearly equal, there will be too much earth; were the angles of the plan re-entering, instead of salient, the result would be reversed. Bearing this in mind, previous to commencing the excavation of the ditch, a correct calculation must be made to prevent any excess, or deficiency of earth for the parapet, and banquette.

_Rules._

1. _To find the quantity of earth_ required for the parapet, and banquette of a field work, &c.

Divide the parapet, and banquette into trapezoids, and triangles; compute the contents of each separately (_by the rules in_ MENSURATION OF PLANES) and the sum of them will be the superficial content of a section of the parapet, and banquette. Multiply this by the length of the periphery of the redoubt, battery, &c., for the solid content of the parapet, and banquette.

2. _To find, rapidly_, the quantity of earth required for a parapet, and banquette.

Multiply the height of the crest of the parapet, into the sum of the bases of the superior, and exterior slopes; which will give the superficial content, very nearly.

3. _To compute the superficial content of the ditch._

Multiply the depth into the breadth at bottom, to which product add the areas of the escarp, and counterscarp, for the content required.

4. _To find the breadth of the ditch_, of the usual form.

Divide the area of the section of the parapet by the intended depth of the ditch, and the quotient will be the mean breadth of the ditch; to this add half the sum of the bases of the slopes of the escarp, and counterscarp, for the breadth at top, and deduct the same for the breadth at bottom.

5. _To find the breadth of the ditch_, having a triangular section.

Divide the area of the section of the parapet by half the given depth of the ditch, and the quotient will be the required breadth at the top.

_Construction of Field works._—_Vide Plate._

_Fig. 1. The redan._

Draw a base line, 60 yards, from the centre of which erect a perpendicular, 40 yards; join the terminations of the base, and perpendicular, which will form the crest of the parapet of the work.

_Fig. 2. The lunette._

Construct a redan (_vide No. 1_), base 80 yards, perpendicular 50 yards: make the faces of the lunette 45 yards in length, and draw the flanks to points on the base line, 30 yards, from the perpendicular.

_Fig. 3. The square redoubt._

Construct a square, each side 40 yards (_vide_ PRACTICAL GEOMETRY). To form additional faces when required, bisect the side of the square, draw perpendiculars inwards equal to ⅛th of the side, and join the termination of the perpendiculars, and the sides of the square, thus forming a double number of faces.

_Fig. 4. The pentagonal redoubt._

Describe a circle, radius 30 yards, and construct a pentagon in the circle (_vide_ PRACTICAL GEOMETRY), thus forming the crest of the parapet of the redoubt.

_Fig. 5. The hexagonal redoubt._

Describe a circle, radius 30 yards, and construct a hexagon within it (_vide_ PRACTICAL GEOMETRY); the sides of which form the crest of the parapet of the work.

_Fig. 6. The circular redoubt._

Describe a circle, radius 30 yards, which will form the crest of the parapet of the redoubt.

_Fig. 7. The star fort, with six points._

Construct an equilateral triangle, and divide each side, 75 yards, into three equal parts, form also an equilateral triangle on the central portion of each side, 25 yards, and the crest of the parapet of the fort will be traced.

_Fig. 8. The star fort, with eight points._

Construct a square: divide each side, 60 yards, into three equal parts, and on the central portion, 20 yards, describe an equilateral triangle: the periphery of the fort will thus be obtained.

_Fig. 9. The field fort, with bastions, and half bastions._

Construct a square; from the centre of each side, 120 yards, drop a perpendicular equal to one-eighth of the side, through the extremity of which, from the angles of the square, draw the lines of defence; make the faces of the bastions, and half bastions, two-sevenths of the exterior side, and draw the flanks perpendicular to their respective lines of defence.

[Illustration: FIELD FORTIFICATION.

_J. W. Lowry, sc._]

_Fig. 10. The bridge head, or tête du pont._

Construct a redan, base 50 yards, perpendicular 30 yards, at an appropriate distance from the bridge, 50 yards; draw flanks, 20 yards, perpendicular to the faces, and from their termination draw lines to the river parallel to the capital of the work. To strengthen the defence of the tête du pont, construct a flèche, faces 20 yards each, and 10 yards in front of the bridge, 4 yards wide.

In the construction of bridge heads, the foregoing Figures may be employed when expedient; the simplest form, the redan, being for light bridges, and the more perfect defence, the bastioned front, or fronts, for bridges of material consequence.

_Fig. 11, 12, 13. Lines._—_Vide Plate._

_Fig. 11._ Construct a redan, base 40 yards, perpendicular 30 yards; which join by a curtain 100 yards, to a queue d’aronde.

_Fig. 12._ Side of square, 35 yards, and lines drawn from summit to points on the curtains 10 yards. To increase the defence of the next curtain, 100 yards, bisect it by a perpendicular, 15 yards, and draw the two faces. Lengthen the lines by cremaillères.

_Fig. 13._ Base 100 yards; crochet, base 5 yards; perpendicular 20 yards.

_Lines, continuous_, are formed by a modification of redans, lunettes, curtains, &c., dependent on the nature of the ground, and the means of defence.

_Lines, with intervals_, are formed by detached redans, lunettes, &c., within range of each other; the rear works flanking those in front.

_Bridges, and passages_ into field works are from 6 feet, to 12 feet wide, according to the requirements.

_Traverses_ are placed about 9 feet from the slope of the banquette, their length being so regulated as to exclude from the view of the enemy the interior of the field work.

The nature, and form of the field work, or lines, required for the defence of a post, &c., &c., having been determined, the perimeter may be laid down, in conformity to the construction detailed in the foregoing figures: after which the requisite dimensions of the parapet, ditch, &c., (dependent, of course, on the nature of the enemy’s ordnance) must be taken into consideration, and the quantity of earthwork computed by the _Rules_, page 245, or by those in PRACTICAL GEOMETRY. The following Table will, however, in many cases be found useful; and, by a judicious adaptation of it, much time may be saved in the computation, and construction of field works.

TABLE,

showing the dimensions, in feet; and the superficial content of earth of banquettes, parapets, and ditches, of field works.

Key: A = Number. B = Base of slope. C = Tread. D = Height. E = Base. F = Superficial content. G = Berm. H = Breadth at top. I = Escarp slope. J = Counterscarp slope. K = Depth.

+----+-----------------+----------------------------------------+ | | BANQUETTE. | PARAPET. | | +---+---+---+-----+---------+---------+---------+----------+ | | | | | | Interior| Superior| Exterior| | | | | | | | slope. | slope. | slope. | | | | | | | +----+----+----+----+----+----+ | | A | B | C | D | F | D | E | D | E | D | E | F | +------------+---+-----+----+----+----+----+----+----+----------+ | 1 | 6 | 5 | 3 | 24 | 7½ | 1½ | 7½ | 15 | 5½ | 5½ | 120½ | | 2 | 6 | 4 | 3 | 21 | 7½ | 1½ | 7½ | 15 | 5 | 5 | 113⅞ | | 3 | 6 | 5 | 3 | 24 | 7½ | 1½ | 7½ | 12 | 5½ | 5½ | 101 | | 4 | 6 | 4 | 3 | 21 | 7½ | 1½ | 7½ | 12 | 5 | 5 | 98⅜ | | 5 | 6 | 4 | 3 | 21 | 7½ | 1½ | 7½ | 9 | 5½ | 5½ | 81½ | | 6 | 6 | 4 | 3 | 21 | 7½ | 1½ | 7½ | 9 | 5½ | 5½ | 81½ | | 7 | 5 | 4 | 3 | 19½ | 7½ | 1½ | 7½ | 6 | 6 | 6 | 66⅜ | | 8 | 5 | 4 | 3 | 19½ | 6 | 1 | 6 | 6 | 4½ | 4½ | 44-6/8 | | 9 | | | | | 8 | 1½ | 8 | 12 | 5½ | 5½ | 102⅛ | | 10 | | | | | 7½ | 1 | 7½ | 9 | 5½ | 5½ | 78 | | 11 | | | | | 6 | 1 | 6 | 6 | 4½ | 4½ | 44⅝ | | 12 | | | | | 6 | 1 | 6 | 3 | 5¼ | 5¼ | 33-15/16 | | 13 | 4 | 4 | 3 | 18 | 7½ | 1 | 7½ | 4 | 5½ | 5½ | 44¾ | +----+---+---+---+-----+----+----+----+----+----+----+----------+

+---+-----------------------+ | | DITCH. | + +----+----+---+---+-----+ | | | | | | | | | | | | | | | | | | | | | | G | H | I | J | K | F | +---+----+----+---+---+-----+ | 3 | 26 | 3 | 3 | 6 | 138 | | 3 | 20 | 4 | 4 | 8 | 128 | | 3 | 23 | 3 | 3 | 6 | 120 | | 3 | 17 | 4 | 4 | 8 | 104 | | 3 | 19 | 3 | 3 | 6 | 96 | | 3 | 16 | 4 | 4 | 8 | 96 | | 2 | 18 | 3 | 3 | 6 | 90 | | 2 | 15 | 10 | 5 | 8 | 60 | | 3 | 19 | 3 | 3 | 6 | 96 | | 2 | 16 | 4 | 4 | 6 | 72 | | 2 | 12 | 4 | 3 | 6 | 51 | | 2 | 9 | 6 | 3 | 8 | 36 | | 2 | 15 | 10 | 5 | 8 | 60 | +---+----+----+---+---+-----+

SIMPLE METHODS OF TRACING FIELD WORKS, ON THE GROUND.

_1. Square redoubt._

Place pickets in a line (in length conformable to the side of the intended work), at each end of which erect perpendiculars equal in length to the side first marked out, and join the termination of these lines; which will complete the perimeter of the redoubt.

_Note._—A perpendicular is raised on a given line, with a chain or cord, by forming a right-angled triangle from the numbers 3, 4, and 5, or any multiples thereof, and extending the cord, &c., so that the base may correspond with the base line of the pickets, and the perpendicular be in the direction of the side required.—_Vide_ PRACTICAL GEOMETRY.

_2. Pentagonal redoubt._

With a chain, tape, or cord, construct, and lay down with pickets five similar, and contiguous triangles, having their bases, which form the sides of the pentagon, in the proportion of 47 to the other two equal sides, the length of each of these being 40.

_3. Hexagonal redoubt._

From a central point with a chain, or line, construct, and lay down with pickets six equilateral, and contiguous triangles, the bases of which will form the required hexagon.

_4. Octagonal redoubt._

Construct a square (_vide_ No. 1), from the centre of each side of which erect perpendiculars outwards, in length proportional to the side as 13 to 60 (nearly 1 to 5); join the extremities, or termination of the perpendiculars, to the angles of the square, which will determine the sides of the octagon.

_Note 1._—The directions for the construction of the pentagonal, and hexagonal redoubts are on a small scale; but the redoubts may be increased by the equal extension of the interior sides of the triangles, until the bases are sufficiently long for the periphery of the work required.

_Note 2._—By means of the pocket sextant, prismatic compass, or reconnoitring protractor, the pentagonal, hexagonal, and octagonal redoubt may be thus traced on the ground. From a central point place pickets at the requisite distance from each other, and in the direction of lines drawn from the angle of the centre of the intended work. (_Vide_ PRACTICAL GEOMETRY. _To find the angles at the centre, and circumference of a polygon._) Extend these radii equally until the relative distances between them are of the length required to form the sides of the proposed equilateral redoubt.

_5. Front of fortification, for a Field fort._

Place pickets in a straight line, of the length required for the front of the proposed field work; from the centre of which drop a perpendicular inwards, making it for a square, pentagon, hexagon, or octagon, respectively one-eighth, one-fifth, one-fourth, or one-third of the exterior side. Direct the lines of defence from the termination of the exterior side to the end of the perpendicular, making the faces of the bastions two-sevenths of the exterior side, and constructing the flanks perpendicular to, and joining the lines of defence. Other fronts are traced by laying down the exterior sides, at the angle of the circumference of the intended polygon (_Vide_ PRACTICAL GEOMETRY) by means of the prismatic compass, &c., and then proceeding as directed for the former front.