These attacks and counter-attacks had brought the German and French trenches so close together that it became impossible to fight in the open. The struggle was therefore continued underground. On both sides subterranean galleries were bored under the opposing trenches, generally to a depth of 20 to 26 feet. Mine-chambers, filled with cheddite, at the end of the galleries, were fired electrically. In the ensuing upheaval the trenches entirely disappeared, giving place to huge craters, for the possession of the edges of which bitter hand-to-hand fighting followed.
BRITISH CEMETERY, BETWEEN ALBERT AND LA BOISSELLE, ON THE RIGHT.
BRITISH GRAVES IN THE GREAT MINE CRATER AT LA BOISSELLE.
During the night of February 6, 1915, the Germans fired three mines in the southern part of La Boisselle occupied by the French, and captured the craters, but were unable to debouch from them. The next day a spirited French counter-attack drove them back.
The communiqués of 1915 mention many feats of this kind, and to-day the traces which still remain of this ferocious struggle attest its extreme violence.
On each side of the Albert-Bapaume road, opposite La Boisselle village, huge craters form an almost continuous line.
The largest crater lies on the right. It has a diameter of about 200 feet and a depth of 81 feet. British graves lie at the bottom (photo opposite).