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, were built at the entrance with huge guns creating a "Triangle of Fire" that could theoretically thwart any invasion attempt by sea. Fort Casey is now a 467 acres (1.89 km2) marine camping park. The Admiralty Head Lighthouse is located in the state park.
Construction on Fort Casey was started in 1897. Her big guns on disappearing carriages, which could be raised out of their protective emplacements so that the guns were exposed only long enough to fire, became active in 1901. Unfortunately, the fort's batteries became obsolete almost as soon as their construction was completed. The invention of the airplane in 1903, and the subsequent development of military aircraft made the fort vulnerable to air attack. In addition, the development of battleships designed with increasingly accurate weaponry transformed the static strategies of the nineteenth century into the more mobile attack systems of the twentieth century. Most of Fort Casey's guns and mortars were removed and sent to Europe and the Pacific during World War II, where they were mounted on railcars to serve as mobile heavy artillery.
In 1935, the Coast Artillery withdrew the station's battery assignments and placed it on inactive status. As World War II approached, military officials reactivated the station after making physical improvements to the aging frame-plaster construction.
The two 10-inch (25-cm) seacoast artillery guns on disappearing carriages at the fort were salvaged in the mid-1960's from their final active duty location at Fort Wint on the U. S. Naval Base Subic Bay, and are scarred with the effects of the Japanese bombings in the Philippines at the opening of World War II. Two 3-inch (76-mm) rapid-fire guns from Fort Wint are also mounted at Fort Casey.