(c) The trenches should have the best possible cover.
(d) The forward position on a slope for the first line has the best advantage. The support trench should be on the reverse slope from 100 to 600 yards in rear of the first line to prevent direct observation and to be practically free from artillery fire. The reserve trench is usually from ½ to 1 mile in rear of the first line. Remember that the first line, the support line, and the reserve line are all fire trenches. Do not put them on a crest.
(e) The communicating trenches (boyaux) should be zigzagged, wide and deep, and should follow the low ground. The longest straight trench should not exceed thirty paces. The angle made by each turn should be less than 140 degrees.
(f) The fire trenches should have salients and re-entrants so as to flank the wire entanglements. The bays are usually 27 feet long with 9 feet of traverse.
(g) There are two problems in the siting of trenches, one for those to be constructed under fire and another for those that will be constructed without any danger from fire. Trenches built under fire are usually made by connecting up individual shelters made by the front line when forced to halt. Trenches built under quiet conditions can be laid out according to the best possible plan.
Trench Construction.
Several kinds of difficulties face the trench digger: Sand, clay, water and bullets. In order to overcome them he must be familiar with the general arrangement of a trench, the principles which govern its construction and the standard trench as it has been worked out in the present war at the cost of thousands of lives.
General Arrangement.—A position is a combination of trenches, consisting of: The fire trench, or first line, nearest the enemy; the cover trench, just behind the first line, where all but sentinels of the fire trench garrison are held in dugouts or shelters; the support trench, from 150 to 200 yards in rear of the cover trench, and the reserve, from 800 to 1,200 yards still further to the rear.
The support trench is placed far enough from the first line to prevent the enemy from shelling both trenches at once. By a concentration of artillery fire and a determined advance of the hostile infantry the first line may be captured. The support trench must be so organized that it will then act as a line of resistance upon which the enemy's advance will break. Lieutenant Colonel Azan of the French army says: "As long as the support trenches are strongly held, the position is not in the hands of the enemy."
