Fort Casey State Park is located on Whidbey Island in Washington state. 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 at the entrance with huge guns creating a "Triangle of Fire." This military strategy was built on the theory that the three fortresses would thwart any invasion attempt by sea. Fort Casey is now a 467-acre (1.89 km²) marine camping park.