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The position of our army before Sebastopol has forced upon the attention of those even who were most peaceably disposed details of military operations to which we have long been strangers. With many of the terms employed most well-informed persons are familiar; but there are others purely technical, which belong to war considered as an art or a science. With these the non-professional reader cannot be supposed to be well acquainted. We propose, therefore, to give a brief sketch, first, of the operations which it is probable that an army would perform when establishing itself in an entrenched position ; and, secondly, of the plan ordinarily pursued in besieging a fortified place.
We will suppose, then, that a well-appointed army finds itself unexpectedly in the presence of a vastly superior force; or that, for some other reason, its commander feels disposed neither to give battle nor to retreat. We will suppose, also, that he has the power of selecting his own ground; and that he has in his rear facilities for retiring, should necessity for such a movement present itself.
A rising ground, with a precipice, river, or morass on either flank, or on both, and not commanded by any ground of superior or even equal elevation, would afford an eligible site for an entrenched position, which would be rendered yet more advantageous by a river, marsh, or other such natural obstruction in front. Such a position, indeed, might be said to be well defended by nature. A careful and skilful general, however, would not rest satisfied with these natural defences, but would avail himself of the appliances afforded by the science of Fortification, which may be defined, “ the art of putting a place in a state to resist the attack of an enemy.
Officers of the engineers first measure the ground on which it is proposed to erect a field-work (this being the name given to fortifications not intended for permanent use), and wooden stakes, called pickets, are driven in as a guide to the workmen who are about to be employed. Labourers from the neighbouring villages are sometimes hired to assist in this operation ; but it is frequently performed exclusively by fatigue-parties of the soldiers themselves, who have stated duties assigned to them, and are relieved at regular intervals. They commence by excavating a ditch or trench to the depth of about twelve feet, more or less, according to circumstances.
The soil thus removed, called the déblai, is thrown up on the side which the defenders intend to occupy, and ought to furnish sufficient remblai to form a parapet of a thickness proportioned to the weight of metal that the enemy are likely to bring to bear upon the position. The face of the trench next the defenders is termed the escarp, that next the enemy is the counterscarp; the front of the parapet is allowed to take the natural slope of the earth thrown up, which varies according to the tenacity of the soil. It is prevented from falling back into the trench by leaving between its base and the edge of the escarp a narrow ridge called the berm. As it is, of course, intended that the defenders should stand within the work, the parapet is made of a convenient height for a man of ordinary stature to fire over it. The inside, or rear of the parapet, is not, like the front, allowed to take the natural slope of the earth, but is made to approach much nearer the perpendicular. This is effected either by building it up with sods reserved for that purpose, by fascines, bundles of rods tied together, if wood be easily attainable, by bags of earth, or by gabions, cylindrical baskets of wicker-wood. This process is called reveting, and the work itself thus constructed, a revetment; which method is adopted must depend in a great measure on the nature of the soil, the facilities within reach, &c. The defenders are frequently elevated on an earthen platform, which runs round the parapet, and is called the banquette, that part on which they actually stand being called the tread. The banquette is ascended by a sloping earthwork called the ramp.
At certain parts of the work, where it is considered that artillery can be used with effect, platforms are constructed with the most solid material that can be obtained, and batteries of cannon are planted, their fire being directed through openings cut in the parapet, and called embrasures.
Besides these internal defences, other measures are adopted to strengthen the work and check the approach of an enemy, so as to keep him as long as possible exposed to the fire of the defenders. For instance, the ground is raised at the crest of the counterscarp and made to slope towards the enemy; not, as might be supposed, for the sake of deepening the trench, but to shelter the parapet from the fire of the enemy's field-pieces: this is called the glacis. Care is also taken to cut down any woods and to destroy any houses which might afford him cover. The trees felled have all their leaves and smaller branches cut off, and with their larger branches sharpened are placed in a row on the ground, securely fastened together, with their points turned in the direction from which the assault is expected. This defence is termed an abattis. Chevaux de frise are long beams through which are inserted sharp stakes at right angles to each other, so that, even if turned over, one row of spikes always projects towards the assailants. The extremities of the beam are sometimes fixed to a frame, in such a way that the engine itself revolves on a pivot when pressed against. Where cavalry can manæuvre with advantage, the ground is strewed with crow's feet, or caltrops, which are spikes fastened together by their heads in such a way that when thrown on the ground, one spike at least always points upwards. Trous de loups (wolf's holes) are pits sloping to a point in which a sharp stake is fixed.
Palisades are rows of stout stakes fastened together by transverse bars. They are sometimes placed horizontally on the parapets, when they are termed fraises.
In spite of these and other such-like obstructions, a determined enemy will sometimes approach so near that the parapet becomes a protection to both parties; but for this emergency the defenders will have prepared themselves by flanking works. The work at either extremity has been constructed so as to take a sudden turn outwards: these projections are termed flanks ; and are of such a nature that fire from their parapets commands the trenches and the glacis; consequently the enemy, should he succeed in reaching the counterscarp, finds himself exposed to a fire from the right and left, as well as from the front. The flanking defences have various names, such as bastions, demi-bastions, &c., and the work which connects two such flanking works is called the curtain.
We read in the account of the siege of Sebastopol that certain batteries were liable to be “enfiladed” by the enemy's fire. By this is meant that the enemy had planted guns to the right or left of the enfiladed battery, in a position where they could not be touched themselves, but from whence they were enabled to do much mischief by firing in a direction nearly parallel to the parapet. This enfilade fire is very dangerous, as the enemy, by employing a small charge of powder, is enabled to practise with advantage ricochet firing; that is, making the shot bound along the battery, dismounting the guns, and sweeping the parapet of its defenders. A parapet thus commanded must either be abandoned or defiladed by the erection of a mound or traverse of sufficient height and solidity to protect the battery on the exposed side.
We have spoken as yet of a work simply intended to repel the attack of an enemy advancing in a given direction ; but it is evident that a large army occupying an extensive field of operations would require many such works as that described, and must expect to be attacked on more points than one. Every one has heard how the Duke of Wellington was enabled to keep his army within the lines of Torres Vedras, having the sea in his rear, from which he obtained his supplies, and to defy all the efforts made by a superior force not equally well-supplied, to dislodge him.
By these “lines” we are not to suppose that his works consisted of one continuous trench and parapet flanked at intervals by bastions, but of a great number of detached works, some advanced much in front of the others, and all varying in their structure to suit the inequalities of the country and the importance of the position.
It is usual to divide field-works into three classes: first, openworks are those which have neither parapet nor trench in the rear; secondly, works which are enclosed all round; and thirdly, lines, properly so called. Of open works the simplest is a redan, or flêche, and is composed of two faces, each from thirty to forty yards long, forming an angle, the apex of which projects towards the enemy. The open part of this and of similar works is called the gorge. Fig. 1 represents a redan, one of the sides of which has a flariking shoulder. Sometimes two redans are united, and form what is termed a double redan (Fig. 2). · This form of work
possesses the great advantage over the single redan, that the adjacent faces flank each other. Open gorged works are mostly constructed much in advance of the main works, and it is desirable that they should be commanded by the fire from other works in the rear, in order that, if taken by the enemy, they may be of no use to him.
To the second class belong redoubts, star-forts, and bastion-forts. A redoubt (Fig. 3) is a rectangular work enclosed on all sides, with
from 20 to 30 yds.
the exception of a narrow opening or doorway at the rear, which may be defended by a drawbridge. At a short distance from this opening, and inside the fort, it is usual to erect a traverse, of sufficient mass and height to protect the soldiers standing at the parapet in front, in case the enemy should attack it in the rear. It should here be observed, that any projecting angle, or angle
which includes a part of the work, is termed a salient angle. A star fort (Fig. 4) is an enclosed work of six or eight salient angles and the same number of re-entering angles.