For this purpose a sufficient number of boyaux are dug in the direction of the enemy, starting from the advanced trenches, passing under the wire entanglements, and connecting together with a cross-trench when at the required distance. This is the “trench of attack” and at the proper time, steps are made in it to facilitate the egress of the troops at the moment of assault.
This work is done at night, and preferably, when possible, by troops which are not to take part in the attack. The men proceed to this work under cover and patrol guard.
Artillery. The artillery, according to its size, is placed between the lines or behind them. Field batteries are pushed forward up to the “artillery protecting line” and placed in position to shell, at any time, certain designated portions of the enemy’s front. They are either buried in the ground or sheltered under casemates, when the latter can be concealed from the enemy.
The trench-guns are, generally, on account of their small range, placed in the first-line support trenches.
The heavy artillery, farthest back of all, is drawn up in echelons according to its size and the part assigned to each part of it.
Wire Entanglements. The width of the wire entanglements varies considerably. Well-strung wire prevents any attack, and none can be attempted until the entanglements are destroyed. In front of their new lines on the Aisne, where the Germans are simply holding the ground, and have given up all notion of advance, they have stretched eight or nine successive rows of wire, each row being fifty metres wide.
Wherever defence only is contemplated, the protection of wire is essential, but it will be well to bear in mind that too many entanglements may prove inconvenient at the time of an attack. We have seen that in such cases, the difficulty is solved by digging communication trenches under the wires.
3. Mines and counter-mines. Since both parties dug themselves in, much use has been made of mines and counter-mines, especially in 1915 and a part of 1916.
The aim of the mine is to throw the enemy into sudden consternation and disorder, while destroying an advanced trench, or work. The French considered the mine as a weapon with which it would be possible to remedy at certain points the defects of their line.
They caused heavy losses to both parties, but are not so much used now for the very good reason that, where the fronts have undergone no change since 1914, the soil has been so greatly disturbed that it would be absolutely impossible to make the necessary excavations. We shall simply recall that in June, 1917, the British, prior to their attack on Messines, set off twenty mines, each containing twenty-three thousand kilograms of explosive, and as the Germans were not aware of their construction, the effect of the explosions was terrible, producing huge craters, seventy metres deep and several hundred metres in circumference.