February 10, 1917—2.30 P.M.
When neither time nor material is lacking, the machine-gun shelters ([Fig. 5]) in the trenches are installed within steel cupolas, which are either stationary or revolving. The mechanism of the latter is, however, complicated, and too delicate for use in the first lines. These cupolas are also much used for observation posts, and, as we shall see later, they are kept as much as possible concealed from the sight of the enemy by camouflage.
Fig. 5
The first line comprises three positions or trenches. That nearest to the enemy is the advanced trench, and at a short distance behind it are the support trenches. Only a few men are now posted as sentries in the advanced trenches. In front of these trenches, “listening” or “watch” posts are hidden in the ground. Between these posts and the advanced trenches barbed wire entanglements are stretched, in number and width proportionate to the dangers threatening the position.
In the support trenches are the dugouts sheltering the men against the fire of the artillery. Many communication trenches or boyaux connect them with the advanced trenches, facilitating the rapid occupation of the latter in case of need. In the advanced trenches are built shelters for the machine-guns. Rifle-fire is directed through loopholes protected by the steel plates above mentioned ([Fig. 4]) which are bullet-proof at fifty yards.
At some distance to the rear of the support trenches and overlooking them, the first-line system is reinforced by a line of “centres of resistance,” which is punctuated with blockhouses protected by thick wire entanglements. Well sheltered machine-guns, a certain number of which sweep the communication-ways leading to the front, compose their main armament. This blockhouse line is connected by many communication-ways with the trenches in front of it.
These centres of resistance are intended to check the advance of the enemy, when they succeed in breaking into the three anterior lines, and to give the reserves time for counter-attacking.
Between the blockhouses and the second-line system a fortified line is frequently organized which is called the “protecting line of the artillery.” This is intended to repel the advance of the enemy infantry, if they gain possession of the first-line system, before they reach the field batteries, or to retard it long enough to allow the batteries to fall back. This line is held by the troops of the sector which do not belong to the fighting contingent.
The distance from the first-line system of trenches to the second-line system varies according to the configuration of the ground. These second lines should, when possible, overlook the first lines, so as to hold them under their fire. The same rules prevail in the location of the third lines. In the sectors which seem to particularly interest the enemy, very strong “check positions” are prepared in the rear.