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Course of Tactics.-Field Fortification.

COURSE OF TACTICS,

LECTURE FIFTH.

The Course of Tactics, of which this is the fifth lecture, is the first part of a complete body of the ART OF WAR, through which we propose to go, distributing it into three parts or divisions, i. e. the Course of Tactics, Practical Engineer. ing, and Strategy. The Course of Tactics will include field fortification and permanent fortification. Practical Engineering will comprehend Military surveys, Planning, Taking up ground, and artillery. Strategy will comprehend military essays on the general detail of war, the duties of general and staff officers, principles of military movements, &c.

FIELD FORTIFICATION.

The method of constructing Field Works continued. 10th, THERE is another method by which to prevent an enemy's passing a defile; this consists in having a double or cross fire, which may be obtained in two different ways: first, (vide plate 3d,). by constructing the redoubt, with the face opposed to the defile tenailled, that is to say, forming a re-entering angle a; by this means it is defended by the fire of the side a b, also by that of the side a e, so that the enemy will be unable to pass through the village d, over the bridge c, and the dam f, which form the defile, any other way than under the fire of the musketry.

11th, The second method is to defend the defile by two redoubts, (vide plate 4th,) whose faces a and b defend the passage, flanking each other at the same time. A farther security may be procured by joining the redoubts with a line d, leaving a passage of thirty or forty feet at each extremity, ee; so that if the enemy should unfortunately succeed in forcing the defile x, troops may be immediately marched to drive them back, and be able afterwards to regain their post. These passages, instead of being covered by traverses, as in redoubts, in order to facilitate such sorties or sallies, are simply closed up with chevaux-de-frise, which may be removed at any time.

Some cases may occur, when it will be necessary to strengthen redoubts of this kind by lines, carried on as far as where the access is nearly impracticable, to prevent the enemy's turning them, and attacking the garrison in their rear. A line, for instance, may be 30

VOL. I. NO. VI.

Course of Tactics.-Field Fortification.

added from the redoubt on the left, to the morass f, through which runs a small brook h; another line may also be added from the redoubt on the right to the deep ravine g, that covers its flank, and in which the trees are all to be cut down. When such lines as these are used to strengthen a work, you must be cautions not to extend them beyond musket-shot, or above three hundred paces; but if the distance they require being carried to should prove greater, a cross-fire then must be obtained by breaking the line, and this of course will improve the defence. In the construction of works intended to dispute the passage of a defile, you must always endeavour to present, if possible, a greater front to the enemy than they can occupy in making the attack.

12th, There are several other works, which are of essential service for defending the passage of a defile, and which indeed deserve the preference, when unprovided with cannon. For instance, the redoubtes en crémailliere, in which the inside line of the parapet is broken in such a manner as to resemble the teeth of a saw : their advantage consists in rendering the passage of the defile more difficult, by means of opposing a greater fire than common redoubts do.

They are constructed as follows. If two hundred and forty men, or one hundred and twenty file, are appointed for the defence of such a work, you have thirty file to each face. Trace a square redoubt, a, b, c, d, (plate 5th,) let each face be thirty paces with an angle presented to the defile. Now divide the faces a b and a d into as many parts, twelve feet each, as those faces will allow, and mark the divisions with small pickets e, but remember always to begin at the angle a. Then construct a fleche upon each of these divisions, the faces of which are eight feet and a half. To perform this operation with facility, use the cord mentioned in the first section; take seventeen feet of it, the sum of the two faces of the fleche, fix the extremities at the ends of each division, stretch the middle of it out towards the front, and mark the angle of the fleche with a small picket, as expressed very distinctly in the plate. Next, trace out a line, determining the thickness of the parapet, parallel to a b and a d; this must be at least fifteen feet, that it may not be too weak at the salient angles

(

Course of Tactics.-Field Fortification.

of the fleches. Two feet will be sufficient for the breadth of the berm: the ditch must be twelve feet wide and six deep, that you' may have earth enough for the parapet. The banquette is made parallel, not to the crémaillieres or teeth, but to the faces a baud a d, (vide plate 6.)

13th, Sometimes redoubts are made quite open in the rear, in order to defend such defiles in front of a camp as are too distant to be battered by the musketry fire of the line. These redoubts are also constructed to sustain the advanced posts on the farther side of the defiles, or to afford them protection if forced to retreat, by preventing the enemy from pursuing them. They are likewise to be erected on heights or eminences, within reach of the cannon of the line, that the enemy may not hold the possesssion of them. Particular care must always be taken to support the detachments that defend them; however, if they should chance to be forced, the enemy can gain but very little advantage, as they are entirely exposed to the fire of the camp, as the work is not closed in its rear; yet a row of chevaux-de-frise should be placed in the opening, well fastened together with chains or cramp-irons; but in case wood cannot be procured to make the chevaux-de-frise, then you must dig trous-de-loup along the rear, to be protected against a surprise in the night. The nature of the ground will determine the figure of these works, and according to the number of men appointed to defend them, 'you will take proper dimensions. (Vide plate 7, fig. 1, 2, 3, 4.)

14th, If you wish to construct a star-work, you must first trace the parapet line of a square redoubt, and divide each face into two equal parts, which you mark with small pickets. From these pickets draw a perpendicular line towards the centre of the work; this line is to be exactly an eighth of one of the faces. This operation is minutely expressed in the plate, (vide plate 8, fig. 1st,) for the use of those officers, who, being unacquainted with geometry, might find these directions rather too abuse. Let us suppose the garrison to be composed of two hundred and fifty-six men, or one hundred and twenty-eight file, which divided by four will make thirty-two file, and consequently as many paces for each face of the redoubt e f g h. The eighth part of each face is four

Course of Tactics.-Field Fortification.

paces, which being set off from their centres towards the middle of the work, and the extremities a bed marked with pickets, you trace lines from these pickets to the angles e f g h, which form the line of the parapet of the star-work. The parapet, the berm, and ditch, follow the same proportions as above directed, traced outwards parallel to the star, as well as the banquette withinside. In these redoubts you obtain a cross-fire, and you have the advantage that the lines mutually defend each other. The entrance is to be made in that part which is the least exposed to be attacked, and always in a re-entering angle. If you cover it with a traverse, this must be broken in the like manner as the face which stands before it.

We have been supposing that thirty-two file were to line each face in the first trace of the square; but as by forming the star we bave increased the line of the parapet, it might be thought that the garrison would be insufficient; the difference, however, is but very inconsiderable: you need but open your files a little more than usual to render it imperceptible, and the defence will be equally good.

15th, You may construct other kinds of star-works by using the following method: trace out a square redoubt a b c d, (vide plate 8, fig. 2d,) divide each face into three equal parts, and trace out an equilateral triangle e fg, on the centre divisions of each. On account of this operation the line of the parapet is increased one fourth. In tracing the square, therefore, three-fourths only of your number of them are to be considered as belonging to the defence of the face, the other fourth is to be left for the triangles. Suppose, for example, your number to consist of one hundred and sixty file: when you trace the square as the foundation of the work, you must allow only one hundred and twenty file, or one hundred and twenty paces to the line of the parapet, which makes thirty to each face; the fourth part, or forty file that remain, are to be placed in the equilateral triangles, when you have completed the star-work, ten file to each triangle. The entrance must be made in a re-entering angle h.

16th, There is another method of constructing star-works, Trace out first an equilateral triangle ABC, (plate 8th, 'fig. 3d,)