beachhead

nouns

a bridgehead on the enemy's shoreline seized by an amphibious operation
"the Germans were desperately trying to contain the Anzio beachhead"
beachhead
is a type of (narrower)
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
an initial accomplishment that opens the way for further developments
"the town became a beachhead in the campaign to ban smoking outdoors"; "they are presently attempting to gain a foothold in the Russian market"
beachhead, foothold