Leslie Groves oversaw construction.
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 1940 Groves , who `` had a reputation as a doer , a driver , and a stickler for duty '' , became special assistant for construction to the Quartermaster General , tasked with inspecting construction sites and checking on their progress . He directed the enormous construction effort , made critical decisions on the various methods of isotope separation , acquired raw materials , directed the collection of military intelligence on the German nuclear energy project and helped select the cities in Japan that were chosen as targets .