The approaches at a siege are generally carried on upon the capitals of the works attached; because the capitals produced are of all other situations in the front of a work the lead exposed to the fire of either the cannon or musquetry; and are the least in the line of fire between the besieged and besieger’s batteries. But if, from particular circumstances, these, or other advantages do not attend the approaches upon the capitals, they are by no means to be preferred to other positions.
The trenches of communication, or zig-zags, are 3 feet deep, 10 feet wide at bottom, and 13 feet at top, having a berm of one foot, beyond which the earth is thrown to form a parapet.
The parallels or places of arms of the trenches are 3 feet deep, 12 feet wide at bottom, and 17 or 18 feet wide at top, having a banquette of about 3 feet wide, with a slope of nearly as much. See the word [Sap].
The first night of opening the trenches, the greatest exertions are made to take advantage of the enemy’s ignorance as to the side of attack; and they are generally carried on as far in advance as the first parallel, and even sometimes to the completion of that work. The workmen set out on this duty, each with a fascine of 6 feet, a pick ax, and a shovel; and the fascines being laid so as to lap one foot over each other, leaves 5 feet of trench for each man to dig.
The usual method of directing the trenches or zig-zags, is by observing during the day some near object in a line with the salient parts of the work, and which may serve as a direction in the night; or if the night be not very dark, the angles of the works maybe seen above the horizon; but as both these methods are subject to uncertainty, the following is proposed, to answer every case: having laid down the plan of attack, the exact positions of the flanked angles of the works of the front attacked, and particularly of those most extended to the right and left, mark on the plan the point of commencement for the first portions of zig-zag; the point where it crosses the capital; and the point to which it extends on the other side of the capital: this last point will be the commencement of the second branch; then mark off the point where this branch crosses the capital and its extent on the other side; and this will give the commencement of the third branch; and so on for the others. Thus provided with a plan ready marked off, it will be very easy, even in the darkest night, to lay down the points where the zig-zags are to cross the capital, and the points to which they are to be produced beyond them. The first parallel is generally run about 600 yards from the place, and of such extent as to embrace the prolongations of the faces of all the works which fire upon the trenches; and each end has a return of about 30 or 40 yards.
The second parallel is constructed upon the same principles, and of the same extent as the first; at the distance of about 300 yards from the salient angles of the covert way. This parallel is usually formed of gabions, each workman carrying a gabion, a fascine, a shovel, and a pick ax. After this the trenches are usually carried on by [sap.—See that word].
The half parallels are about 140 or 150 yards from the covert way, and extend on each side sufficient to embrace the prolongation of the branches of the covert way.
The third parallel must not be nearer than the foot of the glacis, or it will mask the ricochet batteries. It is generally made rather wider than the other parallels.
Cavaliers of the trenches must not be nearer than 28 yards from the covert way, or they will be liable to be annoyed by hand grenades.
See likewise the words [Approaches], [Sap], and [Battery].