Wiktionary
fire trench
n. (context military English) A deep trench from which one can fire on the enemy.
WordNet
fire trench
n. a trench especially constructed for the delivery of small-arms fire
Usage examples of "fire trench".
Several of the children were asleep by the fire trench and I saw Jarek Mace stroll away from the hollow to walk to the brow of a nearby hill.
I stalked a deer close enough to kill it with my spear, and came back with the antlers on my head and the hide wrapped around me, and jumped the fire trench, and they put the Spear Mark on my chest.
Nevertheless, they made a camp resembling a small fort, with an earthen rampart around it, and a fire trench.