The Manhattan Project
Main article: Manhattan Project
The secret U.S. project to create the first atomic weapon was known as the Manhattan Project. Working in collaboration with the United Kingdom and Canada, with their respective projects Tube Alloys and Chalk River Laboratories, the project designed and built the first atomic bombs. The scientific research was directed by American physicist J. Robert Oppenheimer and the overall project was under the authority of General Leslie Groves, of the U.S. Army Corps of Engineers. The Hiroshima bomb, a gun-type bomb called "Little Boy," was made with uranium-235, a rare isotope of uranium extracted in giant factories in Oak Ridge, Tennessee. The atomic bomb was first tested at Trinity Site, on July 16, 1945, near Alamogordo, New Mexico. The test weapon, "the gadget," and the Nagasaki bomb, "Fat Man," were both implosion-type devices made primarily of plutonium-239, a synthetic element created in nuclear reactors at Hanford, Washington. Preliminary research began in 1939, originally because of fear that Nazi Germany would develop atomic weapons first. By early 1945, the defeat of Germany caused attention to turn to possible use against the Japanese.