Fort Casey Historical State Park

Fort Casey was a 19th-century defensive fortification built on Whidbey Island, Island County, Washington, to deter invasion from the sea. It is preserved as Fort Casey Historical State Park, a Washington state park and historic district within the Ebey's Landing National Historical Reserve. Admiralty Inlet was considered so strategic to the defense of Puget Sound in the 1890s that three forts-Fort Casey on Whidbey Island, Fort Flagler on Marrowstone Island, and Fort Worden at Port Townsend-were built with the intention to create a "triangle of fire" against invading ships. This military strategy was based on the theory that the three fortresses would thwart any invasion attempt by sea.