Battery Cooper, built in 1906, had two 6-inch rifles mounted on disappearing carriages that popped up, disappeared, and reappeared like a jack-in-the-box. When the guns were fired, the recoil automatically lowered them behind the concrete wall, protecting the crews while they reloaded, and counterweights returned them to the firing position. During World War I, the U.S. Army removed the guns for possible use as railway guns in France. The guns there today came from the Smithsonian Institution.