For another hundred and fifty yards the party proceeded before the men turned into the zigzag communication-trench. This ran backwards for nearly a mile. In places it was eight feet deep, with sand-bags on either side in addition, In others, in marshy spots, where the high-explosive shells had spitefully disturbed the tranquillity of meandering streams and carried the sluggish water to overflow and swamp the surrounding ground, the "trench" was above normal ground-level, with a lofty and broad wall of sand-bags to right and left. Here and there the trench was roofed in, where, from experience, men had learnt it was unhealthy owing to being exposed to machine-gun fire. The Huns had got to know the weak spots. Aerial observation during daylight had enabled them to train machine-guns upon certain points of the communication-trenches. The lethal weapons would be ominously silent until after dark; then, on the off-chance of receiving a good bag, they would let loose a hail of bullets.