Fighting the Boche Underground

by H. D. Trounce

The preceding sketch illustrates a plan adopted by the French which may be used in suitable soil for the offensive. This procedure often gives good results in deceiving the enemy. He thinks he is protecting himself. The defensive gallery starts from the front line and the offensive from the support. Both galleries are in the same vertical plane, the second being more advanced in the direction of the enemy. In the top galleries very little attempt is made to deaden the noise, while work below is carried on silently. An enemy listener easily confuses one with the other, and the offensive gallery passes under him. Distances D and D¹ are the same. The miner M confuses the two sounds, and the offensive gallery passes under him.

(Note: In many of the districts in France, where a sandy clay forms the top-soil and a hard chalk the subsoil, this method could only be adopted with difficulty, as the conditions are reversed. The top gallery being in clay, it would be comparatively easy to do noiseless work there, but extremely difficult to carry on the lower chalk gallery without noise.)

Referring to sketch C, direct attack may be made in this manner, or this method might be used as a feint, while the enemy is driven around behind the gallery at another point.

The usual measures of precaution employed in ordinary warfare above ground must be taken below ground whenever the distance of the enemy and the nature of the soil do not exclude all possibility of a mining attack.

It is essential to have: An efficient lookout and listening service (observation of enemy's work above ground, and listening-posts above and below); Means of defense underground—countermines.

The most reliable information will be obtained by underground listening with portable listening-instruments, such as the geophone, etc. Much confirmatory evidence is obtained by listening patrols at night in "No Man's Land" and by a careful survey of enemy trenches.

Several different arrangements can be adopted. The fan-shaped arrangement as shown in Fig. B, or the arrangement of independent parallel galleries (Fig. C). The second arrangement is preferable. The interval between galleries varies with range of listening in different soils. In clay, the distances between galleries should not be greater than 60 feet. In chalk this may be safely doubled. Listening-galleries are usually put out in Y-form, and these galleries are of smaller size, often 3 feet by 2 feet in cross-section. If desired, holes may be bored from the ends of these listening-galleries and geophones placed in them. Where time, material, and personnel permit, the mine-shaft is put in at the support-line instead of from the front line. This can only be done, however, when the situation allows of it. The galleries in Flanders seldom reach a greater depth than 25 feet to 30 feet, but in the districts farther south, in the chalk country, mining operations are conducted at any depth from 80 to 150 feet. A comprehensive German mine system was found in the Somme district at 200 feet. Naturally, it is a distinct advantage to get one's own defensive system in first and then sit tight and listen for enemy work.

The best defensive is often a strong offensive. A concrete instance of this is furnished by the experience of a British mining company who were ordered from Flanders to trenches in the chalk district at the Vimy Ridge to meet what was termed "an urgent situation" underground. The Germans were mining from chalk galleries at depths varying from 60 to 100 feet, and inflicting heavy casualties on the infantry occupying the British trenches by blowing large mines under their advanced positions. As a result the infantry were obliged to abandon many of these forward positions. The hard chalk subsoil of this district was covered with a sandy clay top-soil varying in thickness on this sector from 1 to 30 feet in depth. Some defensive galleries in the chalk had been started by the French miners when occupying these trenches. The British at once undertook the construction of numerous galleries in the clay top-soil. Their rate of progress was much faster in clay than that of their opponents in chalk, in addition to which they could proceed without noise. The programme was daring but entirely successful. The enemy continued to handicap their efforts at the outset by blowing often, but within some six weeks the British had succeeded in completely establishing their mastery underground. A few camouflets were blown by them in crossing "No Man's Land," but the majority of their mines were fired directly below the enemy's first line, and in some cases beyond. So intense was the fighting that on some occasions the British blew as many as four mines a night on a 500-yard front.

The question of the blowing and occupation of craters is usually determined in consultation with the infantry staff. Some occasions occur, as, for instance, when the enemy is met below ground, when it is necessary to fire charges which will form craters; but, as a rule, no craters are blown in "No Man's Land" until the infantry have been warned and plans made for their occupation or otherwise.