Part 9

1st. The spot on which works are to be constructed should determine their figure; nor should any attention be paid to preserve a regular form which does not occupy the ground to advantage.

2d. Every line must be so disposed, that the slope of hills all around even to the very bottom, be open to the small arms of the garrison; and every part should be discoverable to the distance of at least 500 paces.

3d. Works thrown up for the defence of a defile, should always be within musquet shot of it, which must not be more than 200 yards.

4th. The best defence in works that are flanked, or where one side is defended by the fire of another, is that formed by right angles.

5th. A salient angle should never be less than 60, and a re-entering angle than 90 degrees; nor greater than 120 degrees.

6th. The entrance to the work should always be made in the part least exposed to attack, and if possible in a re-entering angle.

7th Endeavor to present, if possible, a larger front to the enemy than he can occupy in making the attack.

8th. Avoid all ground commanded by an eminence, either in front, flank, or rear.

9th. Never leave the rear of a work so exposed that the enemy may turn it.

10th. Always make the angles of a work in the directions least exposed to attacks, and consequently always present a front to the most exposed.

11th. The garrison should never be drawn up more than two deep; and an ordinary pace of two feet is usually allowed for each file, and from 6 to 8 paces from each piece of ordnance.

12th. If a work is so large as to be defended by a battalion or two, a reserve should be allowed of about one sixth of the number.

13th. The space within a work should always be sufficient for the men to move and lie down. Every soldier will require at least 18 square feet, and every field gun at least 216 square feet.

14th. Provided the line is not made too extensive, the more inward space there is the better.

15th. A parapet to resist cannon shot should never be less than 12 feet thick; and for musquet shot not less than 6 feet.

16th. The height of the parapet must be regulated by the situation of the work, and of the adjoining ground; with this consideration, that its height above the banquette does not exceed 4½ feet.

17th. The depth and breadth of the ditch must be regulated by the quantity of earth required, for the parapet and banquette.

18th. A tete de pont, or work to cover the embarkation of troops, or the passage of a river, should, if possible, be made where the line of the river or coast forms a kind of re-entering angle; that the flanks of the corps, as well as those of the works, may be covered.

_To carry on the Work._—The number of workmen must be proportioned to the time allotted for carrying on the work, the quantity of labour, and the number of hands capable of being employed at the same time. When the ditches are broad, the workmen may be posted in two rows; but if narrow, only in one. In the first case, the earth will be thrown by those who are on the outward edge of the ditch to the second row, and by them upon the parapet; for which reason the second row, to keep pace with the first, ought to be twice as numerous. The workmen should never be placed nearer than 2 paces, or 4 feet, from each other; and two men with shovels should be preceded by one with a pickaxe. If more than usual expedition be required, one man with a wheel barrow, or basket, may be added to six or eight with shovels. Another row of workmen should also be placed upon the parapet, to spread the earth and beat it down, as it is thrown up.

In fixing the fascines, three men will be sufficient for every 24 feet of the work, who should be provided with two mallets, a saw, and a handbill, or hatchet.

In order to form some idea of the time in which a field work may be completed, compute the number of cubic feet of earth to be excavated, thus; multiply half the sum of the breadth of the ditch at top and at bottom, by the depth, for the number of square feet in the profile; and this multiplied by the distance between the workmen in feet, will give the number of cubic feet each man has to dig: or being multiplied by the length of the ditch, gives the cubic contents of the ditch. Now, one man is supposed to be able to move 216 cubic feet of earth in a day, during the summer; but this is not always the case. If a field work be completed in 24 hours, it will be as much as the most diligent workmen are capable of. This time is generally allowed for the formation of a weak profile; 48 hours for that of a stronger, with a revetement of fascines; and 72 for the strongest.

The different slopes for the works must depend upon the nature of the soil, and the materials of which the work is composed. The interior slope of the parapet, though it be fascined, should be ⅙ of its height; exterior about ⅔ its height. The slope of the banquette equal to its height. The slope of the scarpe or counterscarpe of the ditch, should be from half its height to its full height, according to the soil. The superior slope of the parapet must entirely depend upon the situation of the work, and that of the surrounding country. The interior slope of the parapet is generally lined with fascines, to keep up the earth; but it is not absolutely necessary to fascine the exterior slope, if the soil be pretty stiff. The embrazures are generally made 20 inches wide on the inside, and 9 feet on the outside; they must always be lined with something to retain the earth; turf is generally preferred, as fascines are so apt to take fire.

The manner of making the materials for field works, may be seen under the heads _Fascines_, _Gabions_, _Hurdles_, &c. and the manner of estimating the quantity of materials for works of this kind, may be seen under the word _Battery_.

_Fortification—Permanent._

A _parapet_, to resist cannon, should never be less than 18 feet thick in earth, and 8 or 9 in masonry. A wall need only be two feet thick in masonry, to resist musquetry. The parapet should always be 4½ feet above the banquette, and 7½ or 8 feet above the rampart, or terre plein.

The _Rampart_ should always be sufficiently wide to allow for the platform, and for two carriages passing each other; about 9 fathoms at top. A parapet of earth, though it takes more room, is always preferable to one of masonry, when it can be raised; though the only objection to the masonry is the number of splinters it produces.

Entire _Revetements_ of masonry are not advantageous for the same reason. The masonry of revetements should not be so high as to be seen or battered from a distance: earth parapets are battered in vain, as the earth forms a natural slope.

The best _Escarpe_ is made of masonry, either in wet or dry ditches, be the earthen one ever so well fraized or palissaded. The earthen one may be stormed without making a breach. The escarpe should be 30 or 35 feet high.

The _Counterscarpe_ should also be of masonry, and not less than 12 feet high. The inconveniences of an earth or low counterscarpe, are the impossibility of defending to the last the covert way; as the enemy may descend into the ditch, and again mount the covert way, and so get in the rear of the traverses. The enemy may find his way along the natural slope of an earth counterscarpe, and is not delayed by a tedious operation of getting into the ditch. Besides, the natural slope of the end of an earth traverse prevents its effectually covering the covert way.

_Ditches_ are generally 15 or 18 toises wide. Dry ditches are always preferable to wet ones, on account of the shelter they afford the troops, and the ready communication with the outworks, without the constant trouble and danger of bridges.

The _Covert way_ should be 5 toises wide; less would crowd the troops, and more would allow room for the enemy to erect batteries in it.

The whole of the glacis should be seen, not only from the crest of the parapet, but from the embrazures in the parapet.

The _Tenaile_, must not be so high as to prevent the flank guns in one bastion seeing the breach that may be made in the collateral one.

_Ravelins_ are best without flanks; their faces directed to 10 toises from the shoulders of the bastions.

The crest of the parapet of the body of the place should be 8 feet above the crest of the glacis, to command it across a ditch of 15 or 20 toises.

The crest of the parapet of the ravelin is 3 feet lower than that of the body of the place, in order that it may be more effectually commanded from the place; and therefore to enable the parapet of the ravelin to command its own glacis, the ditch is only made 10 toises, and this glacis is a foot lower than that of the body of the place.

There must be an equilibrium of defence established through every front of a fortified place; for it will be needless to strengthen any particular front, if the others from their weakness be left exposed. The following remarks may enable an observer to appreciate the value of particular works, in the proper application and arrangement of which that equilibrium consists.

_Intrenchments_ within the works add much to their defence. In large bastions with obtuse flanked angles, the best intrenchment is formed of the front of a fortification, or of two demi bastions and a curtain, connecting the angles formed by the flank and curtain. If this intrenchment be advanced to the shoulders of the bastion, so as to include its flanks, as is often the case, it will be subject to be taken in the rear, by the fire from the counter batteries opposed to the flanks. But in bastions with acute flanked angles, which do not afford sufficient space for this kind of intrenchment, Cormontaigne proposes one in the form of a cavalier, whose faces and flanks are parallel to those of the bastion. The first kind of intrenchment does not operate in the defence of the place, till after the passage of the ditch; till which time it remains entire, and then capable of a very great defence. The second kind becomes a support to the bastion from the first commencement of the siege; but it is therefore subject to have its defences destroyed at a distance. Nor is its defence equal to that of the other form.

_Counterguards_ should possess the three following properties: 1st. They must cover effectually the principal work before which they are placed; at least that part of it, which can be battered in breach. 2d. They must be lower than the work which they cover; but not so low as to permit its revetement to be seen. 3d. They must be so narrow as not to afford room for the besiegers to erect batteries in them, against the work which they cover, and therefore not leave the besiegers a choice of positions. The counterguards in Coehorn’s system are only of earth, through which it is necessary to make an opening, before the capital work can be battered.

_Horn_ or _Crown Works_, unless to occupy some important point, to strengthen some weak side, or to afford more room for a confined garrison, are rather a weak than a strong arm to a place. This is particularly the case when they are constructed with smaller, and consequently weaker fronts, than that part of the body of the place which they cover; as they facilitate, when taken, the approaches to the body of the place. This is remedied by constructing their fronts of the same strength as the front or fronts which they cover. They also facilitate the taking of the place, by exposing the revetement of the work on which their branches are directed, to be battered in breach, along the ditches of those branches. This is a great evil, even to an outwork, but is of serious consequence if they rest upon the body of the place. This defect has been remedied by placing these works altogether outside of the covert way, and allowing their ditch no communication with those in the rear. In this case their gorge must be made very secure to prevent its being turned.

An _Advanced Covert_ way, is esteemed amongst the best means of adding to the defence of places. Besides the advantages common to the usual covert way, it has many peculiar to itself. It however seems necessary to ensure to it the many advantages of which it is susceptible, (beside being properly palissaded,) that it should be secured in the rear by a wet ditch, as the only means of giving it an inaccessible counterscarpe, and at the same time keeping it under the fire of the musquetry of the place. This kind of covert way is generally supported by redoubts upon the capitals of the bastions and ravelins; which from their position cannot mask the fire of the place; and being mounted with artillery, oblige the besiegers to commence their attack at a great distance, and very much to extend their operations; and as their establishment upon this covert way must effectually mask the fire of their first batteries, it must greatly increase their labour. The retreat from these redoubts must be secured by an underground passage.

_Countermines_ are undoubtedly one of the first means of strengthening places. For this article we refer to the word _Mines_.

_Detached Redoubts_, when circumstances of situation favour them, are employed with great success. They are usually detached and totally unconnected with any of the works of the place, by any covert way or other aboveground work; and have for objects, either the opposing an additional obstacle to the besiegers at the point they occupy, or the rendering the adjoining fronts inaccessible, by an enfilade or reverse fire upon the approaches. They also afford at their gorge, a most excellent rendezvous and retreat for sorties; upon the level of the country, and without the difficulty of filing troops through the barrier of a covert way.

But in order to insure to the detached work or works, all these advantages, it is necessary that they should be either totally inaccessible to the besiegers, by reason of the natural difficulties of their situation, as in an inundation, morass, &c. or be made secure by art, from being taken by storm, and only attackable by regular approaches. They should be under cover of the fire of the place; but if their distance be too great for that, an intermediate work must be established to give them support. Their best form is that of a bastion with retired flanks; and a strong system of countermines the most effectual way of prolonging their resistance.

_General Remarks._—The larger the flanked angles of works, the more direct will be their fire, and that of their covert way, upon the approaches; the greater extent will they oblige the besiegers to occupy in their parallels and batteries; and the more will they oblige the besiegers to expose themselves to the fire of the fronts collateral to the one attacked. Faces of works directed to inaccessible situations, such as rivers, lakes, &c. from whence they cannot be enfiladed by ricochet batteries, add greatly to the strength of a front.

If the flanked angle of a ravelin be so advanced as to see in reverse any battery erected upon the crest of the glacis, or in the covert way of the bastions, it will increase the strength of that front; because it will oblige the besiegers to gain possession of the ravelin, before they can make any lodgement, from which they can batter the bastions. This is the case in Cormontaigne’s system: and a place thus fortified, obliges the besiegers to attack and gain two ravelins, to get at the bastion between them. Beside, if this system be applied to a right line, or to a polygon of many sides, the prolongations of the faces of the bastions, will be intercepted by the flanked angle of the ravelins, and consequently make the establishment of enfilading batteries against them very difficult. A work which admits of a breach being made in it (particularly the body of the place) at a distance, very much facilitates its being taken. The ditch of the ravelin affords an opening through which the besiegers may make a breach in the face of the bastion, from the glacis, opposite the flanked angle of the ravelin, and is therefore subject to this defect. A counterguard before the bastion, lessens this evil, by transferring the breach from the body of the place to the ravelin; but it requires a counterguard also before the ravelin, effectually to cure it. A crown or horn work also produces this evil; its remedy was given, in speaking of those works.

The direction of the flanks or faces of a work is not so material as relating to the fire of artillery, as to that of musquetry; for artillery is never fired without being pointed, but musquetry is fired mechanically, and perpendicular to the parapet, without much attention to the object to be struck.

A work in the neighbourhood of a height must be defiladed[7] from that height, that is, instead of being built upon a horizontal plane, it must be erected upon an imaginary inclined plane, passing from somewhere in the interior of that work, over the most commanding points of the height: and every part of the works must bear the same relation to this inclined plane, that they would do, to a horizontal plane in a level country.

A work is not therefore always to be condemned, because it is in the neighbourhood of a height; for if it be properly defiladed from that height, it will receive a great advantage over the approaches of the besiegers, carried on down an inclined plane towards it. But a work to be properly constructed in the neighbourhood of heights, must not uniformly preserve the same distance from those heights, unless their summits be all upon the same level; but must approach them at their lowest parts, and recede from them as they rise; thus will the necessary plane of defilement preserve nearly the same degree of obliquity throughout.

_The Dimensions in the following Table of Vauban, are thus applied_:

The _Fort_ is mostly for squares.

The _Little_ for citadels, commonly pentagons.

The _Mean_ for all fortifications from the hexagon and upwards.

The _Great_ is seldom used but in irregular fortifications, and particularly on rivers.

[7] The compiler must here apologize for coining the word _defiladed_, which he is obliged to do, never having seen this subject treated of in English. But the French use the word _defile_ in a contrary sense to _enfile_; and as we admit the words enfilade and enfiladed from the latter, we cannot refuse the terms defilade and defiladed from the former.

_Principal Dimensions of Fortifications, according to_ VAUBAN.

+-----------------+-------+-------------+--------+----------+ | |Side of| Length of |Faces of|Capital of| | |Polygon|Perpendicular|Bastions|Ravelins | +-----------------+-------+-------------+--------+----------+ | Forts. | 80 | 10 | 22 | 25 | | | 90 | 12 | 25 | 28 | | | 100 | 12½ | 28 | 30 | | | 110 | 14 | 30 | 35 | | | 120 | 15 | 33 | 38 | | | 130 | 16 | 35 | 40 | | | | | | | | Little | 140 | 20 | 40 | 45 | | Fortification. | 150 | 21 | 42 | 50 | | | 160 | 23 | 45 | 50 | | | 170 | 25 | 47 | 52 | | | | | | | | Mean. | 180 | 30 | 50 | 55 | | | 190 | 31 | 53 | 55 | | | | | | | | Great. | 200 | 25 | 55 | 60 | | | 260 | 22 | 60 | 50 | +-----------------+-------+-------------+--------+----------+

_Dimensions of Walls and their Counterforts, from 10 to 50 Feet high, having a Slope of ⅕ their Height._

+--------------------------------++-----------------------------+ | Wall. || Counterforts. | +--------+-----------+-----------++--------+---------+----------+ | | | ||Distance| | | | | Thickness |Thickness ||between | | | |Height. | at Top. |at Bottom. || them. | Breadth.| Length. | +--------+-----------+-----------++--------+---------+----------+ |Feet. |Feet. Inch.|Feet. Inch.|| Feet. |Feet. In.| Feet. In.| |10 | 4 0 | 6 0 || 8 | 2 8 | 4 — | |15 | 4 3 | 7 3 || 10 | 3 4 | 5 — | |20 | 4 6 | 8 6 || 12 | 4 0 | 6 — | |25 | 4 9 | 9 9 || 14 | 4 8 | 7 — | |30 | 5 0 | 11 0 || 16 | 5 4 | 8 — | |35 | 5 3 | 12 3 || 18 | 6 0 | 9 — | |40 | 5 6 | 13 6 || 20 | 6 8 | 10 — | |45 | 5 9 | 14 9 || 22 | 7 4 | 11 — | |50 | 6 0 | 16 0 || 24 | 8 0 | 12 — | +--------+-----------+-----------++--------+---------+----------+

The heights in the above table are taken only from the bottom of the ditch, and do not include the foundations.

When the rampart is partly walled and partly turfed; then ⅕ of the height of the turfed part must be added to the breadth of the wall at the top given in the table.

The bases of all inward slopes of earth should be equal to their height, if not more.

The bases of all outward slopes of earth ⅔ of their height.

The superior slopes of all parapets ⅙ of their breadth.

The slope of all walls, or revetement ⅕ of their height.

Though the above principles given for the erection of field works may assist an officer’s recollection who may be employed on that duty, the memorandums given respecting _permanent_ fortification pretend to no such object: but may serve to remind an officer, if he should visit a fortification, of its essential requisites; and may assist his observations in passing round the works.

_FUZES.—Composition._

Saltpetre 3 lbs. 4 oz. Sulphur 1 — Mealed powder 2 12