REDOUBT is a general name for nearly every kind of work in the class of field fortifications; thus a redan with flanks, a parapet enclosing a square or polygonal area, a work in the form of a star [star-fort], and a fort with bastions at the angles, like the enceinte of a fortress, are occasionally so called; but the second of these is the work to which the term is more particularly applied, and it is that which we purpose now to describe. When a work to be constructed on level ground is intended to contain troops and artillery for the purpose of preventing the enemy from occupying the spot, and when there is an equal probability that the work may be attacked on any side, that spot should he quite enclosed by the parapet; also if the defence is to continue only till succour can arrive from the army in the vicinity, flanking defences being then scarcely necessary, a quadrangular figure may suflice for the plan of the work, and there can be no reason why one side ■hould be longer than another, or why the sides should form with each other any but right angles. But when the redoubt is to occupy an eminence whose figure on the plan it irregular, the faces of the work, whatever be tho form thus produced, must necessarily be traced so as to correspond to the different directions assumed by the brow of the height; and if the fire of the work is intended to defend some fund object, as a pass leading towards it, one of the faces must be perpendicular to the direction of that pass. It may be observed however that in general the number of fares, though not less than four, should bo as few as possible. The ditches of all polygonal works without re-entering angles, are incapable of being defended by the fire from the parapets above, on account of the height and thickness of the latter, which prevent the soldiers from seeing them; and a curvilinear redoubt has, besides, two defects which are irremediable; the fires from its parapets are diverging, therefore they produce little effect while the enemy is advancing up to the work; and the ditch, on account of its form, is incapable of being defended from stockades within it. These objection' apply with nearly equal force to redoubts formed on regular polygons of more than five or six sides. The French however made a circular redoubt of casks for the purpose uf strengthening the defence of the isthmus at St. Sebastian previously to the siege of that place in 1813; ami circular redoubts of masonry are supposed to be useful on the setcoasts. In the latter situation they are not liable to be attacked by infantry; and their artillery, which is mounted on traversing platforms, may be fired in any direction against ships or boats, should an enemy attempt a debarkation of troops. [martello Towers.]
Every work in field as well as in permanent fortification it surrounded by a ditch, from whence is obtained the earth for the parapet, and by which the difficulty of carrying it bv assault is increased. The ditch is generally crossed direct';opposite the entrance by a bridge of timber, which should be capable of being drawn into the work, or re-placed at pleasure. The entrance into a redoubt is at a re-entering anglr, if there is one, otherwise it may be about the middle of oae of the faces on the side which is least exposed to the view of the enemy; and, besides being barricaded, it is defended bi the fire from a traverse, which is raised in the interior, and perpendicular to the direction of the passage.
Redoubts for the defence of positions are in general intended to contain only about fifty men with three guns: but works in the form of irregular polygons have somctnon been constructed of a magnitude sufficient to contain 16M men and twenty-five pieces of artillery; and such were the two principal redoubts (on Mount Agraea and at Torre* Vedras), formed in 1810, in order to protect Lisbon. Tlieve were expected to make a vigorous defence in the event of being attacked; but it is admitted that thei, trace, or ground-plan, was defective on account of the want of flank*. and perhaps they would have been prevented from faille; only by the strong divisions of troops who were daily umVr arms in their vicinity. The redoubt constructed by the British in the neighbourhood of Toulon, in 1793, for the protection of the town and fleet, was a large work well furnished with artillery; yet, on being attacked by the republican troops, it was taken, after a gallant resistance, in »hirh the enemy was twice repulsed. The ditches being undefended by flanks, the assailants, on being driven into them, re-formed their order with little molestation; and at the third attack they succeeded in getting possession of the work.
It is admitted among military men that in firing orer i parapet, the soldier doing the duty as rapidly as possible', and fearing to expose himself while adjusting his musk*.-:. places the latter mechanically in a direction nearly perpendicular to the line of the face behind which he is station*-*} It follows that in front of every salient angle of the work there must be an undefended sectoral space, as mn, in th# suhjoincd cut, which represents the plan of a square redoubt in which space, in order to avoid the direct fire from the faces, the enemy may advance to the attack; and on thai account it is recommended that the faces of the work slioulj be disposed so that the angles may be turned tosrara* ground which is impassable, or which will not permit tbr enemy to establish batteries for the purpose of enfihadir«£ those faces. When this disposition is not possible, rarucj methods may he adopted by which the troops who man th>e work might direct some of their fire within those sector*. The simplest of these, and that which is generally put a practice, is to form the crest of the parapet near **yt anfta. very little attention on the part of the men about a and b will enable them to give their muskets au oblique direction so as to fire upon an enemy advancing within those spaces. A second method is that of rounding off the interior of the parapet at the angles, as at erf; but this has been objected to on account of the divergency of the lines of fire. The third method, which is much dwelt on by writers on fortification, consists in forming the interior of the parapet with indentations, as at eg and fh, alternately parallel and perpendicular to the capital, each indent being three feet long; and a parapet of this kind is said to be en cremaillere. It is evident that by placing men contiguously to the sides of these indentations, a fire may be kept up in either of the directions just mentioned; and by placing them at the angles, they may fire perpendicularly to the general face of the work. It must be observed however that the men cannot fire in these different directions at the same time, because, the muskets crossing one another, that of one man might be injured by the fire of the next. The only objections to this method are, that the parapet can be so formed only by men belonging to the corps of sappers and miners, who are regularly trained to the construction of fortifications, but who may not be present when wanted; and that the unsteadiness of the soldiers in firing almost always renders such precision in the formation of the work useless.
The ditch of a redoubt having no Hanks, being unseen and incapable of defence from the parapets, it has been proj>osed, in order to have some means of annoying the enemy when in the ditch, to form an enclosed space A, at one or more of the angles of the ditch, by planting a line of palisades across the latter on two contiguous faces of the work; the enclosure may have a roof of timber covered with earth, and loop-holes, three feet asunder, must be cut in the palisades, that the defenders may be enabled to fire along the ditches.
Another method, which may be advantageously adopted when a fare of the work has considerable length, is to form, as at B, what is called a palisade cuponniere, by planting across the ditch, at the middle of the face, two rows of palisades about eight feet asunder; each row being pierced with loop-holes. The entrance into the caponniere is by steps in the interior of the redoubt and a gallery under its parapet; and this work, as well as that at A, may have a roof, but in no case should such roof be above the level of the natural ground, in order that it may be concealed as long as possible from the view of the enemy. One of the redoubts which was executed near Lisbon, being commanded by a height in its front, from whence the parapets might have been destroyed and the interior ploughed by shot, there was formed a gallery behind the counterscarp, and opposite one of the angles of the work, with loop-boles, from whence the ditch along each face might have been defended by musketry if the enemy had penetrated into it. The soil being chalk, no timber-frames were necessary for the support of the sides or top; and between this recess and the interior of the redoubt there was a gallery of communication passing under the bottom of the ditch.
A row of palisades is frequently planted quite along the ditch of a redoubt. Sometimes also the escarp of the work is fraized, or furnished with palisades planted in an inclined position, and a line of chevaux-de frize is disposed upon the berme. In order to retard the advance of an enemy, the work is generally surrounded, at a distance not exceeding the range of musket-shot, by a single or double abatis, and often by two rows of pits called trous de loup. The magnitude of a redoubt, whatever be its form, is determined by the strength of the garrison and the quantity of ordnance by which it is to be defended; all the men being supposed to be lodged within it. It was formerly the practice to allow on the area of the terreplein, within the foot of the banquette, ten square feet for each man, and 324 square feet for each piece of artillery; consequently when the redoubt is of a square form, the breadth of the banquette being known (about 11 feet), the length of the crest-line on each face could be easily determined. In order that the defenders may conveniently use their arms on the banquette, it has been customary to allow three feet along the crest of the parapet for each man, who is to stand contiguously to the interior slope; and it was once considered that a redoubt intended to make a considerable resistance when attacked on all sides, would be adequately garrisoned if the number of men in it were equal to the number of feet in the whole length of the crest of the purupet; that is to say, if there were three ranks of men along each face, the work being supposed to be capable of containing such a number. It is said that each side of the square redoubts which Marshal Saxe caused to he consirucled at the siege of Maestricht in 1748 was above 100 feet long, measured on the crest of the parapet, and that each redoubt was garrisoned by SOU men; and it will be found by computation that, consistently with the above rules, a square redoubt, each of whose faces is sixteen yards long, is the least that ought to be constructed ; for if less, the interior within the banquette would not contain the number of men necessary to line its parapet with one rank. But the rule relating to the area within the banquette has been objected to as an unnecessary affectation of mathematical precision. The British en E'neers who constructed the works for the protection of isbon observe that, except at night, or at the moment of being attacked, part of the garrison will be on watch, or otherwise occupied outside of the work; and even at those times, at least one-thud will be under arms on the banquette. Colonel Sir John Jones states that the strengths of the garrison were finally determined by allowing two men per yard in the length of the parapet for the exterior works, and one man per yard for the interior works; deductions being made for the spaces where artillery was to stand. Each gun takes up about eighteen feet of the length of a parapet.
The crest of the parapet of a redoubt may bo about 8 feet above the natural ground, unless the work is to be defiladed from some commanding ground in the neighbourhood, in which case it must be higher. The form of a seciion or profile of the parapet is similar to that which is used for permanent fortification [lines Op Intrenchment,./?^-. 4], but the breadth of the superior slope may vary with the nature of the arm which the enemy can bring against it; three feet will suffice if the work can be attacked by infantry only, but it may be as much as 10 or 12 feet if it is to resist field artillery of the heaviest calibre. The superior surface of the parapet should slope down towards the exterior, so that the defenders may see the top of the counterscarp of the ditch in front; and when, from the great relief of the work, this is impossible, the counterscarp should be raised by earth obtained from the ditch to the height necessary for this purpose; taking care however to give the raised earth a gentle slope towards the exterior, that the enemy may not be'screened by it. The exterior of the parapet and the escarp of the ditch are covered or reveled with sods when the earth has not sufficient tenacity to stand unsupported; and when the work is to resist the fire of heavy artillery, the revetment might consist of stout logs of timber planted obliquely in the ground or in the bottom of the ditch, and leaning against the face of the work. The interior of the parapet is usually reveted with sods or fascines.
Redoubts are intended to fortify military positions, for which purpose they usually occupy the heights and command the defiles; and their magnitude or number must depend upon the time afforded for their construction. [lines Ok InTrenchment; Military Positions.] It sometimes happens that they are thrown up during a night to protect artillery on the wings, or in some important situation in front of the army, in expectation of an engagement taking place the next day; and then they are necessarily few and small. When Marshal Soult was reduced to defensive operations in the south of France, in 1813 and 1814, he strongly entrenched the heights on all the frontier between the sea about Bayonne and St. Jean-de-Luz, and the mountains at St. Jean-Pied-de-Port; an extent of above 16 miles. The works, which were executed in three months, were generally irregular polygons; and some of them were constructed for 500 men. More than a year was spent in raising the redoubts which covered Lisbon; and consequently these were not only strong, but numerous beyond any other example. [encampment.] They were of every trace, but mostly irregular polygons, whose sides sometimes formed reentering angles, as the ground required: the two great redoubts before mentioned were retrenched by interior parapets, which also served as traverses, and each salient point of the redoubt at Torres Vcdras constituted an independent post. Attack and Defence of a Redoubt.—In the attack of a small redoubt unprovided with artillery, light infantry or riflemen, keeping for a time as much as possible covered by the inequalities of the ground, endeavour to surround the Work, and, by a fire of musketry, directed towards the crest of the parapet, to diminish that of the defenders. The assailing troops then gradually close in upon the redoubt, and, while one division remains on the counterscarp to continue the fire, should the defenders show themselves upon the parapets, the rest descend into the ditch, where, having collected themselves in parties or small columns, they mount the parapet on each side of a salient angle; then developing themselves on the summit, they make a general discharge and enter the work. In order to avoid accidents in descending into the ditch, or in ascending the escarp, it is recommended that the bayonets should not be fixed by the assailants till they have gained the berme of the work.
But if the redoubt is of considerable magnitude, if it is furnished with artillery, and moreover protected by palisades in the ditches, and abatis or other obstacles in the front, the attack must be conducted with more powerful means. It should commence by a fire of artillery directed partly so as to enfilade the parapets, break down the palisades and derange the abatis, and partly to destroy the merlons which cover the artillery of the work. The lire of the latter being thus in some measure silenced, the light infantry, as in the former case, endeavour by musketry to prevent the defenders from manning the parapets; and in the mean time columns of troops advance towards the angles, being preceded by parties of sappers and miners, who make openings for them in the line of abatis, or cover with timbers the trous de loup, if such there be. If the ditch is deep, the descent into it, and the subsequent ascent of the escarp, must be facilitated cither by placing scaling-ladders or by throwing in fascines or bags of hay; and any palisades or other obstacles which may not have been displaced by tiic artillery, must now be cleared away by the working-parties which accompany the troops. The fire of the covering parties must cease while the assailants are mounting the parapet, but it must recommence if they should be repelled: in the latter case the storming troops reform their order in the ditch, and again attempt to enter the work. It may be supposed that at length they will succeed, when the defenders, if not provided with a redoubt to which they may retire for the purpose of capitulating, must surrender at discretion. In 1793 the French camp under Valenciennes was protected by works which, though furnished with artillery, were open at the gorge; and in an attack, the British cavalry, having entered those works at their rear, made prisoners of all the • defenders. When a redoubt is threatened with an attack, the officer commanding it endeavours to provide against the event by disposing in front of the work all possible obstacles to the advance of the enemy, and by placing sand-bags on the parapets in order to cover the defenders, who are to fire through small intervals left for the purpose: these measures should be taken, if not before, during the night preceding the attack; since the latter generally takes place early in tho morning. On the advance of the assailants, the artillery of the work is made to play upon their columns;
and the fire of musketry commences as soon as the latter are within the proper range. These Dies are kept up vigorously while the assailants are clearing awav the obstacles, and until they have descended into the ditcli. Should the work have flanks, and the guns behind them be not Jtv mounted, a fire of grape-shot and of musketry must now be directed along the ditches; while hand-grenades and slon«* are thrown, and live shells are rolled into them from the parapets of the faces. The storming troops may however persevere, and may at length mount upon the parapet, in which case they must be received by a fire of musketry from the defenders on the terreplein; and the latter, if overpowered, must endeavour to retire or capitulate.
Any works constructed within others, in order to prolong their defence, or to afford a retreat for the troops who occupy them, are also called redoubts; but by the French engineers, reduits or retrenchments.
Note - this article incorporates content from The Penny Cyclopaedia of the Society for the Diffusion of Useful Knowledge (1840)