Editing Manhattan Project (section)

{{Short description|World War II Allied nuclear weapons program}}
{{About|the atomic bomb project}}
{{Pp-vandalism|small=yes}}
{{Featured article}}
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{{Use dmy dates|date=July 2023}}
{{Use American English|date=July 2023}}
{{Infobox military unit
| unit_name                     = Manhattan District
| image                         = {{multiple image|border=infobox|perrow=1/2/2/2|total_width=300
| image1 = Time, 3-22 p.m, December 2, 1942. Place, Racquets Court under West Stands of Stagg Field, University of Chicago.... - NARA - 542144.tif
| image2 = K25 Aerial.jpg
| image3 = Hanford B Reactor.jpg
| image4 = HD.4G.053 (10540204545).jpg
| image5 = German Experimental Pile - Haigerloch - April 1945.jpg
| image6 = Trinity Detonation T&B.jpg
| image7 = Atomic bombing of Japan.jpg
}} From top to bottom, left to right: {{flatlist|
* [[Chicago Pile-1]], the first [[nuclear reactor]]
* [[K-25]], the primary [[uranium enrichment]] site
* The [[Hanford Site|Hanford]] [[B Reactor]] used for [[plutonium]] production
* The Gadget [[implosion-type nuclear weapon|implosion]] device at [[Project Y|Los Alamos]]
* [[Alsos Mission|Alsos]] soldiers dismantle the [[Haigerloch research reactor|Haigerloch pile]] of the [[German nuclear weapons program]]
* The [[Trinity test]], the first nuclear explosion
* [[Atomic bombings of Hiroshima and Nagasaki]], the only nuclear attacks in history}}
| dates                         = 1942–1946
| country                       = {{ubl|United States|United Kingdom|Canada}}
| branch                        = [[U.S. Army Corps of Engineers]]
| garrison                      = [[Oak Ridge, Tennessee]], U.S.
| battles                       = {{ubl|style=text-indent:-1em; margin-left:1em;
  | [[Allied invasion of Italy]]|[[Operation Overlord|Allied invasion of France]]
  | [[Western Allied invasion of Germany|Allied invasion of Germany]]|[[Atomic bombings of Hiroshima and Nagasaki]]
  | [[Occupation of Japan|Allied occupation of Japan]]}}
| anniversaries                 = 13 August 1942
| disbanded                     = 15 August 1947
| notable_commanders            = {{ubl|[[James C. Marshall]]|[[Kenneth Nichols]]}}
| identification_symbol         = [[File:Manhattan District.svg|110px|center|alt=Oval shaped shoulder patch with a deep blue background. At the top is a red circle and blue star, the patch of the Army Service Forces. It is surrounded by a white oval, representing a mushroom cloud. Below it is a white lightning bolt cracking a yellow circle, representing an atom.]]
| identification_symbol_label   = Manhattan District [[shoulder sleeve insignia]]
}}

The '''Manhattan Project''' was a research and development program undertaken during [[World War II]] to produce the first [[nuclear weapon]]s. It was led by the United States in collaboration with the United Kingdom and Canada. 

From 1942 to 1946, the project was directed by Major General [[Leslie Groves]] of the [[United States Army Corps of Engineers|U.S. Army Corps of Engineers]]. Nuclear physicist [[J. Robert Oppenheimer]] was the director of the [[Los Alamos Laboratory]] that designed the bombs. The Army program was designated the '''Manhattan District''', as its first headquarters were in [[Manhattan]]; the name gradually superseded the official codename, '''Development of Substitute Materials''', for the entire project. The project absorbed its earlier British counterpart, [[Tube Alloys]], and subsumed the program from the American civilian [[Office of Scientific Research and Development]]. 

The Manhattan Project employed nearly 130,000 people at its peak and cost nearly US$2&nbsp;billion (equivalent to about ${{formatnum:{{Inflation|US-GDP|2|1945|r=0}}}}&nbsp;billion in {{Inflation/year|US-GDP}}).{{Inflation-fn|US-GDP}} The project pursued both [[highly enriched uranium]] and [[plutonium]] as fuel for nuclear weapons. Over 80 percent of project cost was for building and operating the [[fissile material]] production plants. Enriched uranium was produced at [[Clinton Engineer Works]] in [[Tennessee]]. Plutonium was produced in the world's first industrial-scale [[nuclear reactor]]s at the [[Hanford Engineer Works]] in [[Washington (state)|Washington]]. Each of these sites was supported by dozens of other facilities across the US, the UK, and Canada. Initially, it was assumed that both fuels could be used in a relatively simple atomic bomb design known as the [[gun-type fission weapon|gun-type design]]. When it was discovered that this design was incompatible for use with plutonium, an intense development program led to the invention of the [[Nuclear_weapon_design#Implosion-type_weapon|implosion design]]. The work on weapons design was performed at the Los Alamos Laboratory in [[New Mexico]], and resulted in two weapons designs that were used during the war: [[Little Boy]] (enriched uranium gun-type) and [[Fat Man]] (plutonium implosion).

The first nuclear device ever detonated was an implosion-type bomb during the [[Trinity test]], conducted at [[White Sands Missile Range|White Sands Proving Ground]] in New Mexico on 16 July 1945. The project also was responsible for developing the specific means of delivering the weapons onto military targets, and were responsible for the use of the Little Boy and Fat Man bombs in the [[atomic bombings of Hiroshima and Nagasaki]] in August 1945. 

The project was also charged with gathering intelligence on the [[German nuclear weapon project]]. Through [[Operation Alsos]], Manhattan Project personnel served in Europe, sometimes behind enemy lines, where they gathered nuclear materials and documents and rounded up German scientists. Despite the Manhattan Project's own emphasis on security, Soviet [[atomic spies]] penetrated the program.

In the immediate postwar years, the Manhattan Project conducted weapons testing at [[Bikini Atoll]] as part of [[Operation Crossroads]], developed new weapons, promoted the development of the network of [[United States Department of Energy National Laboratories|national laboratories]], supported medical research into [[radiology]], and laid the foundations for the [[nuclear navy]]. It maintained control over American atomic weapons research and production until the formation of the [[United States Atomic Energy Commission]] (AEC) in January 1947.