Editing Nuclear fission (section)

===Manhattan Project and beyond===
{{see also|Manhattan Project}}
In the United States, an all-out effort for making atomic weapons was begun in late 1942. This work was taken over by the [[U.S. Army Corps of Engineers]] in 1943, and known as the Manhattan Engineer District. The top-secret [[Manhattan Project]], as it was colloquially known, was led by General [[Leslie R. Groves]]. Among the project's dozens of sites were: [[Hanford Site]] in Washington, which had the first industrial-scale nuclear reactors and produced [[plutonium]]; [[Oak Ridge, Tennessee]], which was primarily concerned with [[uranium enrichment]]; and [[Los Alamos National Laboratory|Los Alamos]], in New Mexico, which was the scientific hub for research on bomb development and design. Other sites, notably the [[Berkeley Radiation Laboratory]] and the [[Metallurgical Laboratory]] at the University of Chicago, played important contributing roles. Overall scientific direction of the project was managed by the physicist [[J. Robert Oppenheimer]].

In July 1945, the first atomic explosive device, dubbed "The Gadget", was detonated in the New Mexico desert in the [[Trinity test|Trinity]] test. It was fueled by plutonium created at Hanford. In August 1945, two more atomic devices – "[[Little Boy]]", a uranium-235 bomb, and "[[Fat Man]]", a plutonium bomb – were [[atomic bombings of Hiroshima and Nagasaki|used against the Japanese cities of Hiroshima and Nagasaki]].