Leslie Groves oversaw the construction of the Pentagon.
Lieutenant General Leslie Richard Groves Jr. ( 17 August 1896 -- 13 July 1970 ) was a United States Army Corps of Engineers officer who oversaw the construction of the Pentagon and directed the Manhattan Project , a top secret research project that developed the atomic bomb during World War II . In August 1941 , he was given responsibility for the gigantic office complex to house the War Department 's 40,000 staff which would ultimately become the Pentagon .