File:Main Navy Building and Munitions Building on the Washington National Mall, 1918.jpg

English: Main Navy and Munitions Buildings. Photographed from the top of the Washington Monument, circa 1918, looking about west with the Potomac River in the distance. Main Navy is the nearer of the two structures, with nine wings as first completed. The Munitions building had only eight wings. Constitution Avenue, NW, runs along the structures' northern face and 17th Street is in the foreground. Note the many World War I temporary buildings in the area to the north of Constitution Avenue. The Lincoln Memorial is in the left distance, with the Reflecting Pool under construction in front of it. The Naval Hospital is in the right center background, on the near side of the river. The buildings were temporary structures built during World War I on the National Mall in Washington, D.C. The buildings remained in use for several decades, and the Secretary of War was headquartered in the Munitions Building from 1936 until the Pentagon opened in 1943.