The Manhattan Project was the project to evelop the first nuclear weapon (atomic bomb) during World War II by the United States, the United Kingdom, and Canada. Formally designated as the Manhattan Engineer District (MED), it refers specifically to the period of the project from 1941–1946 under the control of the U.S. Army Corps of Engineers, under the administration of General Leslie R. Groves. The scientific research was directed by American physicist J. Robert Oppenheimer.