From Longman Dictionary of Contemporary Englishbridgeheadbridge‧head /ˈbrɪdʒhed/ noun [countable] PMa strong position far forward in enemy land from which an army can go forward or attack
Examples from the Corpus
bridgehead• All we have to do is get in and establish a bridgehead, so to speak.• There were thousands more slaves now, working to finish the bridgehead. 