View along Calwell Trail where it meets the Interpretive Trail Loop. Calwell Trail is an old fort access road that linked Battery Calwell with today's Campground Road. Fort Flagler was established on the north end of Marrowstone Island in 1897. Along with Forts Casey and Worden, Fort Flagler helped defend Admiralty Inlet, the vital passage to the Bremerton Naval Shipyard and ports in Seattle & Tacoma. Today Fort Flagler State Park maintains the same borders as the original fort, with hiking trails, beaches, camping, museum, 5 vacation houses, retreat center and 10 historic gun batteries open for public exploration.