So the gallery crept steadily on. They had to carry the tunnel rather close to the surface because at very little depth they struck more water than any pumps, much less their single farmyard one, could cope with. The nearness to the surface made a fresh difficulty and necessitated the greatest care in working under the ground between the trenches, because here there were always deep shell-holes and craters to be avoided or floored with the planking that made the tunnel roof. So the gallery had to be driven carefully at a level below the danger of exposure through a shell-hole and above the depth at which the water lay. This meant a tunnel too low to stand or even kneel in with a straight back, and the men, kneeling in mud, crouched back on their heels and with rounded back and shoulders, struck their spades forward into the face and dragged the earth out spadeful by spadeful. Despite the numbing cold mud they knelt in, the men, stripped to shirts with rolled sleeves and open throats, streamed rivulets of sweat as they worked; for the air was close and thick and heavy, and the exertion in the cramped space was one long muscle-racking strain. Once the roof and walls caved in, and three men were imprisoned. The collapse came during the night, fortunately, and, still more fortunately behind the line and parapet of the forward trench. The Subaltern flung himself and his men on the muddy wreckage in frantic haste to clear an opening and admit air to the imprisoned men. It took time, a heart-breaking length of time; and it was with a horrible dread in his heart that the Subaltern at last pushed in to the uncovered opening and crawled along the tunnel, flashing his electric torch before him. Half-way to the end he felt a draught of cold air, and, promptly extinguishing his lamp, saw a hole in the roof. His men were alive all right, and not only alive but keeping on hard at work at the end of the tunnel. When the collapse came they had gone back to where their roof lay across the bottom of a shell-hole, pulled a plank out, and--gone back to work. When the tunnel reached a point under the German parapet it was turned sharp to left and right, forming a capital T with the cross-piece running roughly along the line of trench and parapet. Here there was need of the utmost deliberation and caution. A pick could not be used, and even a spade had to be handled gently, in case the sounds of working should reach the Germans overhead. In some places the Subaltern could actually hear the movements and footsteps of the enemy just above him.