Overview

The Manhattan Project was a project by the United States, United Kingdom, and Canada to develop the first nuclear weapon (atomic bomb) during World War II. The project is formally designated as the Manhattan Engineer District (MED), which refers specifically to the project period between 1941 and 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.

The project succeeded in developing and detonating three nuclear weapons in 1945: a test detonation of a plutonium implosion bomb on July 16 (the Trinity test) near Alamogordo, New Mexico; an enriched uranium bomb code-named "Little Boy" on August 6 over Hiroshima, Japan; and a second plutonium bomb, code-named "Fat Man" on August 9 over Nagasaki, Japan.