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[[File:Trinity shot color.jpg|thumb|The [[Trinity test]] of the Manhattan Project on 16 July 1945 was the first detonation of a [[nuclear weapon]].]]
The '''Manhattan Project''' was the program based in the [[United States]] which tried to make the first [[nuclear weapon]]s. The project went on during [[World War II]], and was run by the U.S. Army. The head of the project was General [[Leslie R. Groves]], who had led the building of [[the Pentagon]]. The top scientist on the project was [[Robert Oppenheimer]], a famous physicist. The project cost $2 billion, and created many secret cities and bomb-making factories, such as a laboratory in [[Los Alamos, New Mexico]], a [[nuclear reactor]] in [[Hanford, Washington]], and a [[uranium]] processing plant in [[Oak Ridge, Tennessee]]. 

The Manhattan Project had to find solutions to two difficulties. The first difficulty is how to make the special [[isotope]]s of uranium ([[uranium-235]]) or [[plutonium]]. This process is called separation and is very slow. The United States built very big buildings with three different kinds of machine for separation. They made enough fissionable special isotopes for a few nuclear weapons.  The second difficulty was how to make a bomb that will produce a big [[nuclear explosion]] every time. A weapon with a bad design can make a much smaller nuclear explosion. This is called a "fizzle". In July 1945, the Manhattan Project solved the two difficulties and made the first nuclear explosion. This test of a nuclear weapon was called "Trinity" and was a success.

The Manhattan Project created two nuclear bombs which the United States used against [[Japan]] in 1945. The bombs were called "Little Boy" and "Fat Man." Little Boy was powered by plutonium and was an implosion type bomb, while Fat Man used uranium fuel and was a gun-type bomb. Implosion type bombs used explosives to initiate the nuclear fission reaction. Gun-type bombs fired uranium atoms into the nuclei of other uranium atoms to release energy neutrons from the nucleus, beginning the fission reaction.<ref>{{Cite web|title=Science Behind the Atom Bomb - Nuclear Museum|url=https://ahf.nuclearmuseum.org/ahf/history/science-behind-atom-bomb/|access-date=2025-07-09|website=https://ahf.nuclearmuseum.org/|language=en-US}}</ref>

The founding father of the Manhattan project was Yasin F.
== Espionage ==
[[File:Oak Ridge Wise Monkeys.jpg|thumb|right|300px|A billboard encouraging secrecy among Oak Ridge workers|alt=Uncle Sam has removed his hat and is rolling up his sleeves. On the wall in front of him are three monkeys and the slogan: What you see here / What you do here / What you hear here / When you leave here / Let it stay here.]]
The Manhattan Project operated under a blanket of tight security. This was to prevent the [[Axis countries]], especially [[Nazi Germany]], from accelerating their own nuclear projects or undertaking [[covert operation]]s against the project.<ref>{{harvnb|Jones|1985|pp=253–255}}</ref> The possibility of [[sabotage]] was always present. At times, people suspected sabotage when equipment failed. While there were some problems believed to be the result of careless or disgruntled employees, there were no confirmed instances of Axis-instigated sabotage.<ref>{{harvnb|Jones|1985|pp=263–264}}.</ref> However, on 10 March 1945, a Japanese [[fire balloon]] struck a power line, and the resulting power surge caused the three reactors at Hanford to be temporarily shut down.<ref>{{harvnb|Jones|1985|p=267}}</ref>

Maintaining security was difficult because so many people worked on the project. {{or}} A special [[Counter Intelligence Corps]] detachment handled the project's security issues.<ref>{{harvnb|Jones|1985|pp=258–260}}</ref> By 1943, it was clear that Soviet [[atomic spies]] were trying to penetrate the project. Lieutenant Colonel [[Boris T. Pash]], the head of the Counter Intelligence Branch of the Western Defense Command, investigated suspected Soviet espionage at the Radiation Laboratory in Berkeley. Oppenheimer informed Pash that he had been approached by a fellow professor at Berkeley, [[Haakon Chevalier]], about passing information to the Soviet Union.<ref>{{harvnb|Jones|1985|pp=261–265}}</ref>

The most successful Soviet spy was [[Klaus Fuchs]]. Fuchs was a member of the British Mission who played an important part at Los Alamos.<ref>{{harvnb|Groves|1962|pp=142–145}}.</ref> The 1950 revelation of Fuchs' espionage activities damaged the United States' nuclear cooperation with Britain and Canada.<ref>{{harvnb|Hewlett|Duncan|1969|pp=312–314}}.</ref> Subsequently, other instances of espionage were uncovered, leading to the arrest of [[Harry Gold]], [[David Greenglass]] and [[Ethel and Julius Rosenberg]].<ref>{{harvnb|Hewlett|Duncan|1969|p=472}}.</ref> Other spies like [[George Koval]] remained unknown for decades.<ref>{{cite news|last=Broad |first=William J.|date=12 November 2007|url=https://www.nytimes.com/2007/11/12/us/12koval.html |title=A Spy's Path: Iowa to A-Bomb to Kremlin Honor|newspaper=[[The New York Times]]|pages=1–2|accessdate=2 July 2011}}</ref> People will never know the value of the espionage. One reason was that the [[Soviet atomic bomb project]] was held back by a shortage of uranium ore. The consensus is that espionage saved the Soviets one or two years of effort.<ref>{{harvnb|Holloway|1994|pp=222–223}}.</ref>
{{Further|Nuclear espionage}}

== Manhattan Project Media ==
<gallery widths='160px' heights='100%' mode='traditional' caption=''>
File:Manhattan District.svg|Manhattan District shoulder patch

File:Los Alamos Primer assembly methods.png|Different fission bomb assembly methods explored during the July 1942 conference (sketches created in 1943 by [[Robert Serber]])

File:Manhttan Project Organization Chart.gif|The Manhattan Project Organizational Chart, 1 May 1946

File:Trinity Test - Oppenheimer and Groves at Ground Zero 002.jpg|[[J. Robert Oppenheimer|Oppenheimer]] and Groves at the remains of the [[Trinity (nuclear test)|Trinity test]] in September 1945, two months after the test blast and just after the end of World War II. The white overshoes prevented fallout from sticking to the soles of their shoes.

File:Groves and Chadwick 830308.jpg|Groves confers with [[James Chadwick]], the head of the British Mission.

File:Y-12 Shift Change.jpg|Shift change at the Y-12 uranium enrichment facility at the [[Clinton Engineer Works]] in [[Oak Ridge, Tennessee]], on 11 August 1945. By May 1945, 82,000 people were employed at the Clinton Engineer Works. Photograph by the Manhattan District photographer [[Ed Westcott]].

File:Los Alamos map.gif|Map of Los Alamos site, New Mexico, 1943–1945

File:ChicagoPileTeam.png|Some of the [[University of Chicago]] team that worked on the [[Chicago Pile-1]], the first nuclear reactor, including [[Enrico Fermi]] and [[Walter Zinn]] in the front row and [[Harold Agnew]], [[Leona Woods]] and [[Leó Szilárd]] in the second
</gallery>
== References ==
<references/>
== Related pages ==
*[[Leó Szilárd]]
== Further reading ==
;General, administrative, and diplomatic histories
* {{cite journal|last=Bernstein |first=Barton J. |title=The Uneasy Alliance: Roosevelt, Churchill, and the Atomic Bomb, 1940–1945 |publisher=University of Utah |date=June 1976 |journal=The Western Political Quarterly |pages=202–230 |volume= 29 |issue= 2 |doi=10.2307/448105 |jstor=448105 }}
* {{cite book |last1=Fine |first1=Lenore |last2=Remington |first2=Jesse A. |title=The Corps of Engineers: Construction in the United States |publisher=United States Army Center of Military History |location=Washington, D.C. |year=1972 |oclc=834187 }}
*{{cite journal |last=Frisch |first=David H. |title=Scientists and the Decision to Bomb Japan |url=https://archive.org/details/sim_bulletin-of-the-atomic-scientists_1970-06_26_6/page/107 |journal=Bulletin of the Atomic Scientists |volume= 26 |issue= 6 | pages=107–115 | publisher=Educational Foundation for Nuclear Science| date=June 1970|doi=10.1080/00963402.1970.11457835 |bibcode=1970BuAtS..26f.107F }}
* {{cite book |last=Gilbert |first=Keith V. |title=History of the Dayton Project |publisher=Mound Laboratory, Atomic Energy Commission |location=Miamisburg, Ohio |year=1969 |url=http://www.eecap.org/PDF/Dayton_Project/History/HISTORY_OF_THE_DAYTON_PROJECT.pdf |accessdate=21 July 2011 |oclc=650540359 |archive-date=29 July 2013 |archive-url=https://web.archive.org/web/20130729230854/http://www.eecap.org/PDF/Dayton_Project/History/HISTORY_OF_THE_DAYTON_PROJECT.pdf |url-status=dead }}
* {{cite book |last=Gosling |first=Francis George |title=The Manhattan Project : Making the Atomic Bomb |year=1994 |location=Washington, DC |publisher=United States Department of Energy, History Division |oclc=637052193 }}
* {{cite book |last=Gowing |first=Margaret |authorlink=Margaret Gowing |title=Britain and Atomic Energy, 1935–1945 |year=1964 |location=London |publisher=Macmillan Publishing |oclc=3195209 }}
* {{cite book |last1=Hewlett |first1=Richard G. |authorlink=Richard G. Hewlett |last2=Anderson |first2=Oscar E. |title=The New World, 1939–1946 |location=University Park|publisher=Pennsylvania State University Press |year=1962 |isbn=0-520-07186-7|oclc=637004643 }}
* {{cite book |last1=Hewlett |first1=Richard G. |last2=Duncan |first2=Francis |title=Atomic Shield, 1947–1952 |series=A History of the United States Atomic Energy Commission |publisher=Pennsylvania State University Press |location=University Park|year=1969 |isbn=0-520-07187-5|oclc=3717478 }}
* {{cite book |last=Holloway |first=David |title=Stalin and the Bomb: The Soviet Union and Atomic Energy, 1939–1956 |url=https://archive.org/details/stalinbombsoviet0000holl |location=New Haven, Connecticut |publisher=Yale University Press |year=1994 |isbn=0-300-06056-4|oclc=29911222 }}
* {{cite book |last1=Howes |first1=Ruth H. |last2=Herzenberg |first2=Caroline L. |title=Their Day in the Sun: Women of the Manhattan Project |url=https://archive.org/details/theirdayinsunwom0000howe |location=Philadelphia|publisher=Temple University Press |year=1999 |isbn=1-56639-719-7|oclc=49569088 }}
* {{cite book |last=Hunner |first=Jon |title=Inventing Los Alamos: The Growth of an Atomic Community |url=https://archive.org/details/inventinglosalam0000hunn |location=Norman |publisher=University of Oklahoma Press |year=2004 |isbn=978-0-8061-3891-6|oclc=154690200 }}
* {{cite book |last1=Johnson |first1=Charles |last2=Jackson |first2=Charles |title= City Behind a Fence: Oak Ridge, Tennessee, 1942–1946 |url=https://archive.org/details/citybehindfenceo0000john |location=Knoxville|publisher=University of Tennessee Press |year=1981 |isbn=0-87049-303-5|oclc= 6331350 }}
* {{cite book |last=Jones |first=Vincent |title=Manhattan: The Army and the Atomic Bomb |publisher=United States Army Center of Military History |location=Washington, D.C. |year=1985 |oclc=10913875 }}
* {{cite book |last=Rhodes |first=Richard |authorlink=Richard Rhodes |title=[[The Making of the Atomic Bomb]] |location=New York  |publisher=Simon & Schuster |year=1986 |isbn=0-671-44133-7|oclc=13793436 }}
* {{cite book |last=Schwartz |first=Stephen I. |title=Atomic Audit: The Costs and Consequences of US Nuclear Weapons |location=Washington, D.C. |publisher=Brookings Institution Press |year=1998 |url=http://www.brookings.edu/FP/PROJECTS/NUCWCOST/MANHATTN.HTM |access-date=2011-10-19 |archive-date=1999-02-08 |archive-url=https://web.archive.org/web/19990208221936/http://www.brookings.edu/FP/PROJECTS/NUCWCOST/MANHATTN.HTM |url-status=dead }}

;Technical histories
* {{cite book |editor-last=Ahnfeldt|editor-first=Arnold Lorentz |title =Radiology in World War II |publisher=Office of the Surgeon General, Department of the Army |location=Washington, D.C. |year=1966 |oclc=630225 }}
* {{cite journal |last1=Baker |first1=Richard D. |last2=Hecker |first2=Siegfried S. |last3=Harbur |first3=Delbert R. |title=Plutonium: A Wartime Nightmare but a Metallurgist's Dream |url=http://library.lanl.gov/cgi-bin/getfile?07-16.pdf |journal=Los Alamos Science |issue=Winter/Spring |year=1983 |publisher=Los Alamos National Laboratory |pages=142–151 |accessdate=22 November 2010 |archive-date=17 October 2011 |archive-url=https://web.archive.org/web/20111017034523/http://library.lanl.gov/cgi-bin/getfile?07-16.pdf |url-status=dead }}
* {{cite book |last=Hanford Cultural Resources Program |first=U.S. Department of Energy |year=2002 |publisher=Hanford Site Historic District |title=History of the Plutonium Production Facilities, 1943–1990 |location=Richland, Washington |oclc=52282810 }}
* {{cite book |last=Hansen |first=Chuck |authorlink=Chuck Hansen |series=Swords of Armageddon: US Nuclear Weapons Development since 1945 |title=Volume I: The Development of US Nuclear Weapons |location=Sunnyvale, California |publisher=Chukelea Publications |year= 1995a |isbn=978-0-9791915-1-0|oclc=231585284 }}
* {{cite book |last=Hansen |first=Chuck |series=Swords of Armageddon: US Nuclear Weapons Development since 1945 |title=Volume V: US Nuclear Weapons Histories |location=Sunnyvale, California |publisher=Chukelea Publications |year= 1995b |isbn=978-0-9791915-0-3|oclc=231585284 }}
* {{cite book |last1=Hoddeson |first1=Lillian |first2=Paul W. |last2=Henriksen |first3=Roger A. |last3=Meade |first4=Catherine L. |last4=Westfall |title=Critical Assembly: A Technical History of Los Alamos During the Oppenheimer Years, 1943–1945 |url=https://archive.org/details/criticalassembly0000unse_u2h0 |location=New York|publisher=Cambridge University Press |year=1993 |isbn=0-521-44132-3|oclc=26764320}}
* {{cite journal |last1=Home |first1=R. W. |last2=Low |first2=Morris F. |title=Postwar Scientic Intelligence Missions to Japan |url=https://archive.org/details/sim_isis_1993-09_84_3/page/527 |journal=Isis |volume= 84 |issue= 3 |date=September 1993 |pages=527–537 |publisher=University of Chicago Press on behalf of History of Science Society |doi=10.1086/356550 |jstor=235645 |s2cid=144114888 }}
* {{cite journal|last1=Ruhoff|first1=John|last2=Fain|first2=Pat|title=The First Fifty Critical days|publisher=Mallinckrodt Incorporated|location=St. Louis|date=June 1962|journal=Mallinckrodt Uranium Division News|volume=7|issue=3|accessdate=30 October 2010|url=http://www.mphpa.org/classic/CP/Mallinckrodt/Pages/MALK_Gallery_01.htm|archive-date=30 March 2015|archive-url=https://web.archive.org/web/20150330001357/http://www.mphpa.org/classic/CP/Mallinckrodt/Pages/MALK_Gallery_01.htm|url-status=dead}}
* {{cite book |last1=Serber |first1=Robert |authorlink=Robert Serber |first2=Richard |last2=Rhodes |authorlink2=Richard Rhodes |title=The Los Alamos Primer: The First Lectures on How to Build an Atomic Bomb |url=https://archive.org/details/losalamosprimerf0000serb |location=Berkeley|publisher=[[University of California Press]] |year=1992 |isbn=0-520-07576-5|oclc=23693470 }} (Available on [[commons:Image:Los Alamos Primer.pdf|Wikimedia Commons]])
* {{cite book |last=Smyth |first=Henry DeWolf |authorlink=Henry DeWolf Smyth |title=[[Smyth Report|Atomic Energy for Military Purposes: the Official Report on the Development of the Atomic Bomb under the Auspices of the United States Government, 1940–1945]] |location=Princeton, New Jersey |publisher=Princeton University Press |year=1945 |oclc=770285 }}
* {{cite book |last=Thayer |first=Harry |title=Management of the Hanford Engineer Works In World War II: How the Corps, DuPont and the Metallurgical Laboratory Fast Tracked the Original Plutonium Works |publisher=American Society of Civil Engineers Press |location= New York |year=1996 |isbn=0-7844-0160-8|oclc=34323402 }}
* {{cite book |last=Waltham |first=Chris |title=An Early History of Heavy Water |publisher=Department of Physics and Astronomy, University of British Columbia |date=20 June 2002 |accessdate=30 October 2010 |url=http://www.physics.ubc.ca/~waltham/pubs/d2o_19.pdf |archive-date=6 July 2011 |archive-url=https://web.archive.org/web/20110706210311/http://www.physics.ubc.ca/~waltham/pubs/d2o_19.pdf |url-status=dead }}
* {{cite journal |last=Weinberg |first=Alvin M. |authorlink=Alvin M. Weinberg |title=Impact of Large-Scale Science on the United States |journal=Science, New Series |volume= 134 |issue= 3473 |date=21 July 1961 |pages=161–164 |publisher=American Association for the Advancement of Science |doi=10.1126/science.134.3473.161 |jstor=1708292 |pmid=17818712 |bibcode=1961Sci...134..161W }}

;Participant accounts
* {{cite book |last=Bethe |first=Hans A. |authorlink=Hans Bethe |title=The Road from Los Alamos |location=New York |publisher=Simon and Schuster |year=1991 |isbn=0-671-74012-1|oclc=22661282 }}
* {{cite book |authorlink=Samuel Abraham Goudsmit |last=Goudsmit |first=Samuel A. |title=Alsos |publisher=Henry Schuman |year=1947 |location=New York |isbn=0-938228-09-9|oclc=8805725 }}
* {{cite book |last=Groves|first=Leslie |authorlink=Leslie Groves |title=Now it Can be Told: The Story of the Manhattan Project |url=https://archive.org/details/nowitcanbetolds00grov|location=New York |publisher=Harper & Row |year=1962 |isbn=0-306-70738-1|oclc=537684 }}
* {{cite book |authorlink=Leona Woods|last=Libby|first=Leona Marshall|title=Uranium People |location=New York |publisher=Charles Scribner's Sons |year=1979 |isbn=0-684-16242-3 |oclc=4665032 }}
* {{cite book |last=Nichols |first=Kenneth David |authorlink=Kenneth Nichols |title=The Road to Trinity: A Personal Account of How America's Nuclear Policies Were Made |url=https://archive.org/details/roadtotrinity0000nich |location=New York |publisher=William Morrow and Company |year= 1987|isbn=0-688-06910-X|oclc=15223648 }}
* {{cite book |authorlink=Stanisław Ulam|last=Ulam|first=Stanisław|title=Adventures of a Mathematician |location=New York |publisher=Charles Scribner's Sons |year=1983 |isbn=0-520-07154-9 |oclc= 1528346 }}
== Other websites ==
* [http://ww2db.com/battle_spec.php?battle_id=206 WW2DB: Operation Trinity and the Manhattan Project]


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[[Category:Nuclear weapons]]
[[Category:1940s in the United States]]