Fort Flagler

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 Flagler State Park is a Washington state park on the site of Fort Flagler, a former United States Army fort at the northern end of Marrowstone Island. From Fort Flagler, visitors can see Port Townsend to the northwest, the cranes at the Navy base on Indian Island to the west, and Whidbey Island eastward across Admiralty Inlet.