Fort Flagler (1897-1953) was a coastal fortification created to be the first line of defense designed to prevent a hostile fleet from reaching the Bremerton Naval Yard and the cities of Seattle, Tacoma, and Everett. Part of the Harbor Defense of Puget Sound, Fort Flagler, along with Fort Worden, and Fort Casey would become known as the 'Triangle of Fire'. Named after Brig. Gen. Daniel Webster Flagler, Chief of Ordnance, U.S. Army, who died on 29 March 1899.
Fort Flagler was added to the National Register of Historic Places on May 3, 1976.
Fort Flagler was originally constructed with three coastal gun batteries, Battery Revere, Battery Wilhelm and Battery Rawlins. The contract for the construction of these original gun batteries was awarded 22 Jun 1897, to the Pacific Bridge Company, Portland, Oregon. The batteries were completed in 1899 but not accepted for service until 17 Aug 1902. Two additional batteries, Battery Bankhead and Battery Lee were completed in 1900 and 1902 respectively and they were also accepted for service on 17 Aug 1902. Four additional batteries, Battery Grattan, Battery Calwell, Battery Downes, and Battery Wansboro were completed in 1905-1906 and all were accepted for service on 23 Apr 1907.During World War I, eight of the fort's guns were sent to Europe and converted to field or railway guns and 2 were sent to Canada After the war, the fort population was reduced to a caretaker detachment, and by 1937 many of the troop barracks were demolished due to deterioration. In World War II, new barracks were built, the 1920 era Anti-Aircraft Battery was moved into a 'revised' Battery Rawlins. The remaining heavy guns were removed by the end of WWII, and in 1953 Fort Flagler was officially deactivated and declared surplus the next year.