Sometimes a trenchful of the enemy would fire a volley and half of them disappear through gullies leading to other cover.
1916 — Boyd Cable, Action Front, E. P. Dutton and Company (1916), page 113:
"Beg pardon, sir," said 'Enery Irving with lofty dignity, "but if I 'adn't started this row the 'ole trenchful o' Frenchies would 'ave been 'owling our 'Gawd Save.' […]
1916 — Arthur Gleason & Helen Hayes Gleason, Golden Lads, McClelland, Goodchild & Stewart (1916), pages 95-96:
But when he tumbles in from a gusty night out of a trenchful of mud, with the patter from slivers of shell, then he turns to song and color, odd tricks with the knife, and the tales of an ancient adventure.