General Brehon Somervell provided the major motivating power behind the project Colonel Leslie Groves was responsible for overseeing the project for the U.S. Ground was broken on 11 September 1941, and the building was dedicated on 15 January 1943. Located in Arlington County, Virginia, across the Potomac River from Washington, D.C., the building was designed by American architect George Bergstrom and built by contractor John McShain. military, the phrase The Pentagon is also often used as a metonym for the Department of Defense and its leadership. The Pentagon is the headquarters building of the United States Department of Defense.