bridgehead

nouns

an area in hostile territory that has been captured and is held awaiting further troops and supplies
"an attempt to secure a bridgehead behind enemy lines"; "the only foothold left for British troops in Europe was Gibraltar"
bridgehead, foothold
a defensive post at the end of a bridge nearest to the enemy
bridgehead
is a type of (narrower)
the position where someone (as a guard or sentry) stands or is assigned to stand
"a soldier manned the entrance post"; "a sentry station"
post, station