bunny hole noun an excavation in a fox hole to provide protection from a mortar attack US Korean war usage.
These caves correspond roughly to our “bunny holes,” which are only large enough for one man to huddle in during a mortar barrage. Bunny holes are usually dug so that a man can jump from his fighting-hold into the bunny hole[.] — Martin Russ, TheLastParallel, p. 115, 1957