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The Manhattan Project was a research and development project that produced the first atomic bombs during World War II. It was led by the United States with the support of the United Kingdom and Canada. From 1942 to 1946, the project was under the direction of Major General Leslie Groves of the US Army Corps of Engineers. The Army component of the project was designated the Manhattan District; "Manhattan" gradually became the codename for the entire project. Along the way, the project absorbed its earlier British counterpart, Tube Alloys. The Manhattan Project began modestly in 1939, but grew to employ more than 130,000 people and cost nearly US$2 billion (about $26 billion in 2021[1] dollars). Over 90% of the cost was for building factories and producing the fissionable materials, with less than 10% for development and production of the weapons.[2][3]

Two types of atomic bomb were developed during the war. A relatively simple gun-type fission weapon was made using uranium-235, an isotope that makes up only 0.7 percent of natural uranium. Since it is chemically identical to the most common isotope, uranium-238, and has almost the same mass, it proved difficult to separate. Three methods were employed for uranium enrichment: electromagnetic, gaseous and thermal. Most of this work was performed at Oak Ridge, Tennessee. In parallel with the work on uranium was an effort to produce plutonium. Reactors were constructed at Oak Ridge and Hanford, Washington, in which uranium was irradiated and transmuted into plutonium. The plutonium was then chemically separated from the uranium. The gun-type design proved impractical to use with plutonium so a more complex implosion-type nuclear weapon was developed in a concerted design and construction effort at the project's principal research and design laboratory in Los Alamos, New Mexico.

The following is a timeline of the Manhattan Project. It includes a number of events prior to the official formation of the Manhattan Project, and a number of events after the atomic bombings of Hiroshima and Nagasaki, until the Manhattan Project was formally replaced by the Atomic Energy Commission in 1947.

A large house with a stone chimney, decorated with bunting. An army officer runs a red and blue flag up a flagpole. In the foreground are two men in suits and one in an army uniform.

Los Alamos Laboratory director Robert Oppenheimer (left), Manhattan Project director Major General Leslie Groves (center) and University of California president Robert Gordon Sproul (right) at the ceremony to present the laboratory with the Army-Navy "E" Award in October 1945

A long corridor with many consoles with dials and switches, attended by women seated on high stools.

Operators at their calutron control panels at Y-12. Gladys Owens, the woman seated in the foreground, did not know what she had been involved with until seeing this photo in a public tour of the facility fifty years later.[4]

Strings of black blocks are suspended over a circular hole.

Replica of the German experimental nuclear reactor at Haigerloch destroyed by the Alsos Mission

Explosive stack of the 100 Ton Test

Video of the Trinity nuclear test

Aircraft of the 509th Composite Group that took part in the bombing of Hiroshima and Nagasaki. Left to right: backup plane, The Great Artiste, Enola Gay

Casing of a Fat Man nuclear bomb, painted like the one dropped on Nagasaki

Aerial view of the mushroom cloud.

Aerial view of the Operation Crossroads Able mushroom cloud rising from the lagoon with the Bikini Island visible in the background

1939[edit | edit source]

1940[edit | edit source]

1941[edit | edit source]

  • February 25: Conclusive discovery of plutonium by Glenn Seaborg and Arthur Wahl.[15]
  • May 17: A report by Arthur Compton and the National Academy of Sciences is issued which finds favorable the prospects of developing nuclear power production for military use.[16]
  • June 28: Roosevelt creates the Office of Scientific Research and Development (OSRD) under Vannevar Bush with the signing of Executive Order 8807.[17] OSRD absorbs NDRC and the Uranium Committee. James B. Conant succeeds Bush as the head of NDRC.[18]
  • July 2: The MAUD Committee chooses James Chadwick to write the second (and final) draft of its report on the design and costs of developing a bomb.[19]
  • July 15: The MAUD Committee issues final detailed technical report on design and costs to develop a bomb. Advance copy sent to Vannevar Bush who decides to wait for official version before taking any action.[20]
  • August: Mark Oliphant travels to USA to urge development of a bomb rather than power production.[21]
  • September 3: British Chiefs of Staff Committee approve nuclear weapons project.[22]
  • October 3: Official copy of MAUD Report (written by Chadwick) reaches Bush.[21]
  • October 9: Bush takes MAUD Report to Roosevelt, who approves Project to confirm MAUD's findings. Roosevelt asks Bush to draft a letter so that the British government could be approached "at the top." [23]
  • December 6: Bush holds a meeting to organize an accelerated research project, still managed by Arthur Compton. Harold Urey is assigned to develop research into gaseous diffusion as a uranium enrichment method, while Ernest O. Lawrence is assigned to investigate electromagnetic separation methods. Compton puts the case for plutonium before Bush and Conant. [24]
  • December 7: The Japanese attack Pearl Harbor. The United States and Great Britain issue a formal declaration of war against Japan the next day.[25]
  • December 11: United States declares war on Germany and Italy.[26]
  • December 18: First meeting of the OSRD sponsored S-1 Uranium Committee, dedicated to developing nuclear weapons.[27]

1942[edit | edit source]

1943[edit | edit source]

1944[edit | edit source]

  • January 11: A special group of the Theoretical Division is created at Los Alamos under Edward Teller to study implosion.[56]
  • March 11: Beta calutrons commence operation at Oak Ridge.[57]
  • April 5: At Los Alamos, Emilio Segrè receives the first sample of reactor-bred plutonium from Oak Ridge, and within ten days discovers that the spontaneous fission rate is too high for use in a gun-type fission weapon.[58]
  • May 9: The world's third reactor, LOPO, the first aqueous homogeneous reactor, and the first fueled by enriched uranium, goes critical at Los Alamos.[59]
  • July 4: Oppenheimer reveals Segrè's final measurements to the Los Alamos staff, and the development of the gun-type plutonium weapon "Thin Man" is abandoned. Designing a workable implosion design becomes the top priority of the laboratory.[60]
  • July 20: The Los Alamos organizational structure is completely changed to reflect the new priority.[61]
  • September 2: Two chemists are killed, and Arnold Kramish almost killed, after being sprayed with highly corrosive hydrofluoric acid while attempting to unclog a uranium enrichment device which is part of the pilot thermal diffusion plant at the Philadelphia Navy Yard.[62]
  • September 22: First RaLa test with a radioactive source performed at Los Alamos.[63]
  • September 26: The largest nuclear reactor, the B reactor, goes critical at the Hanford Site.[64]
  • Late November: Samuel Goudsmit, scientific head of the Alsos Mission, concludes, based on papers recovered in Strasbourg that the Germans did not make substantial progress towards an atomic bomb or nuclear reactor, and that the programs were not even considered high priority.[65]
  • December 14: Definite evidence of achievable compression obtained in a RaLa test.[66]
  • December 17: 509th Composite Group formed under Colonel Paul W. Tibbets to deliver the bomb.[67]

1945[edit | edit source]

  • January: Brigadier General Thomas Farrell is named Groves' deputy.[68]
  • January 7: First RaLa test using exploding-bridgewire detonators.[66]
  • January 20: First stages of K-25 are charged with uranium hexafluoride gas.[69]
  • February 2: First Hanford plutonium arrives at Los Alamos.[70]
  • April 22: Alsos Mission captures German experimental nuclear reactor at Haigerloch.[71]
  • April 27: First meeting of the Target Committee.[72]
  • May 7: Nazi Germany formally surrenders to Allied powers, marking the end of World War II in Europe;[73] 100-ton test explosion at Alamogordo, New Mexico.[66]
  • May 10: Second meeting of the Target Committee, at Los Alamos.[74]
  • May 28: Third meeting which works to finalize the list of cities on which atomic bombs may be dropped: Kokura, Hiroshima, Niigata and Kyoto.[74]
  • May 30: Stimson drops Kyoto from the target list.[74]
  • June 11: Metallurgical Laboratory scientists under James Franck issue the Franck Report arguing for a demonstration of the bomb before using it against civilian targets.[75]
  • July 16: the first nuclear explosion, the Trinity nuclear test of an implosion-style plutonium-based nuclear weapon known as the gadget at Alamogordo;[76] USS Indianapolis sails for Tinian with nuclear components on board.[77]
  • July 19: Oppenheimer recommends to Groves that gun-type design be abandoned and the uranium-235 used to make composite cores.[78]
  • July 24: President Harry S. Truman discloses to Soviet leader Joseph Stalin that the United States has atomic weapons. Stalin feigns little surprise; he already knows this through espionage.[79]
  • July 25: General Carl Spaatz is ordered to bomb one of the targets: Hiroshima, Kokura, Niigata or Nagasaki as soon as weather permitted, some time after August 3.[80]
  • July 26: Potsdam Declaration is issued, threatening Japan with "prompt and utter destruction".[81]
  • August 6: B-29 Enola Gay drops Little Boy, a gun-type uranium-235 weapon, on the city of Hiroshima, the primary target.[82]
  • August 9: B-29 Bockscar drops a Fat Man implosion-type plutonium weapon on the city of Nagasaki, the secondary target, as the primary, Kokura, is obscured by cloud and smoke.[83]
  • August 12: The Smyth Report is released to the public, giving the first technical history of the development of the first atomic bombs.[84]
  • August 14: Surrender of Japan to the Allied powers.[85]
  • August 21: Harry K. Daghlian, Jr., a physicist, receives a fatal dose (510 rems) of radiation from a criticality accident when he accidentally dropped a tungsten carbide brick onto a plutonium bomb core. He dies on September 15.[86]
  • September 4: Manhattan District orders shutdown of S-50 liquid thermal diffusion plant and the Y-12 Alpha plant.[87]
  • September 8: Manhattan Project survey group under Farrell arrives in Nagasaki.[88]
  • September 17: Survey group under Colonel Stafford L. Warren arrives in Nagasaki.[88]
  • September 22: Last Y-12 alpha track ceases operating.[87]
  • October 16: Oppenheimer resigns as director of Los Alamos, and is succeeded by Norris Bradbury the next day.[89]

1946[edit | edit source]

  • February: News of the Russian spy ring in Canada exposed by defector Igor Gouzenko is made public, creating a mild "atomic spy" hysteria, pushing American Congressional discussions about postwar atomic regulation in a more conservative direction.[90]
  • May 21: Physicist Louis Slotin receives a fatal dose of radiation (2100 rems) when the screwdriver he was using to keep two beryllium hemispheres apart slips.[91]
  • July 1: Able test at Bikini Atoll as part of Operation Crossroads.[92]
  • July 25: Underwater Baker test at Bikini.[92]
  • August 1: Truman signs the Atomic Energy Act of 1946 into law, ending almost a year of uncertainty about the control of atomic research in the postwar United States.[93]

1947[edit | edit source]

Notes[edit | edit source]

  1. Consumer Price Index (estimate) 1800–2014. Federal Reserve Bank of Minneapolis. Retrieved 27 February 2014.
  2. Nichols 1987, pp. 34–35.
  3. "Atomic Bomb Seen as Cheap at Price". Edmonton Journal. 7 August 1945. pp. 1. http://news.google.com/newspapers?id=yuVkAAAAIBAJ&sjid=KoENAAAAIBAJ&pg=5621%2C2841878. Retrieved 1 January 2012. 
  4. "The Calutron Girls". SmithDRay. http://smithdray1.net/angeltowns/or/go.htm. Retrieved 22 June 2011. 
  5. Rhodes 1986, p. 307.
  6. Rhodes 1986, p. 310.
  7. Hewlett & Anderson 1962, p. 17.
  8. Hewlett & Anderson 1962, p. 20.
  9. Rhodes 1986, p. 332.
  10. Gowing 1964, pp. 40–43.
  11. Hoddeson et al. 1993, p. 18.
  12. Hewlett & Anderson 1962, p. 31.
  13. Zachary 1997, p. 112.
  14. Hewlett & Anderson 1962, p. 27.
  15. Rhodes 1986, pp. 383–384.
  16. Hewlett & Anderson 1962, p. 37.
  17. Roosevelt, Franklin D. (June 28, 1941). "Executive Order 8807 Establishing the Office of Scientific Research and Development". The American Presidency Project. http://www.presidency.ucsb.edu/ws/index.php?pid=16137. Retrieved June 28, 2011. 
  18. Hewlett & Anderson 1962, p. 41.
  19. Gowing 1964, p. 76.
  20. Rhodes 1986, pp. 368–369.
  21. 21.0 21.1 Hewlett & Anderson 1962, pp. 43–44.
  22. Gowing 1964, p. 106.
  23. Hewlett & Anderson 1962, pp. 44–46.
  24. Rhodes 1986, pp. 388–389.
  25. Williams 1960, p. 3.
  26. Williams 1960, p. 4.
  27. Hewlett & Anderson 1962, p. 53.
  28. Hewlett & Anderson 1962, p. 49.
  29. Rhodes 1986, p. 399.
  30. Hewlett & Anderson 1962, p. 75.
  31. Jones 1985, p. 126.
  32. Hoddeson et al. 1993, pp. 42–47.
  33. Gowing 1964, pp. 437–438.
  34. Jones 1985, p. 43.
  35. Jones 1985, p. 75.
  36. Jones 1985, p. 77.
  37. Jones 1985, p. 78.
  38. Jones 1985, p. 81.
  39. Jones 1985, p. 83.
  40. Jones 1985, p. 84.
  41. Hewlett & Anderson 1962, p. 112.
  42. 42.0 42.1 Jones 1985, p. 110.
  43. Hewlett & Anderson 1962, p. 152.
  44. 44.0 44.1 Jones 1985, p. 88.
  45. Hoddeson et al. 1993, p. 69.
  46. Hoddeson et al. 1993, p. 66.
  47. Hewlett & Anderson 1962, p. 130.
  48. Hoddeson et al. 1993, p. 79.
  49. Hoddeson et al. 1993, p. 380.
  50. Nichols 1987, p. 101.
  51. Gowing 1964, p. 171.
  52. Jones 1985, p. 241.
  53. Rhodes 1986, p. 499.
  54. Hewlett & Anderson 1962, p. 211.
  55. Rhodes 1995, p. 103.
  56. Hoddeson et al. 1993, p. 157.
  57. Hewlett & Anderson 1962, p. 164.
  58. Hoddeson et al. 1993, p. 238.
  59. Hoddeson et al. 1993, p. 202.
  60. Hoddeson et al. 1993, p. 240.
  61. Hoddeson et al. 1993, p. 245.
  62. "Explosion at Navy Yard". Manhattan Project Heritage Preservation Association. http://www.mphpa.org/classic/FH/PH/Article_05.htm. Retrieved 9 April 2013. 
  63. Hoddeson et al. 1993, p. 269.
  64. Jones 1985, p. 221.
  65. Goudsmit 1947, pp. 69-79.
  66. 66.0 66.1 66.2 Hoddeson et al. 1993, p. 271.
  67. Jones 1985, p. 521.
  68. Nichols 1987, p. 171.
  69. Hewlett & Anderson 1962, p. 300.
  70. Hewlett & Anderson 1962, p. 310.
  71. Rhodes 1986, p. 609.
  72. Jones 1985, p. 528.
  73. Williams 1960, p. 534.
  74. 74.0 74.1 74.2 Jones 1985, p. 529.
  75. Jones 1985, pp. 532–533.
  76. Williams 1960, p. 550.
  77. Rhodes 1986, p. 670.
  78. Hoddeson et al. 1993, p. 377.
  79. Rhodes 1986, p. 690.
  80. Rhodes 1986, p. 691.
  81. Rhodes 1986, p. 692.
  82. Jones 1985, pp. 536–538.
  83. Jones 1985, pp. 538–541.
  84. Jones 1985, p. 561.
  85. Hewlett & Anderson 1962, pp. 405-406.
  86. McLaughlin, Thomas P.; Monahan, Shean P.; Pruvost, Norman L.; Frolov, Vladimir V.; Ryazanov, Boris G.; Sviridov, Victor I. (May 2000). "A Review of Criticality Accidents". Los Alamos National Laboratory. pp. 74–75. LA-13638. http://www.orau.org/ptp/Library/accidents/la-13638.pdf. Retrieved April 21, 2010. 
  87. 87.0 87.1 Hewlett & Anderson 1962, p. 624.
  88. 88.0 88.1 Jones 1985, p. 544.
  89. Hoddeson et al. 1993, p. 401.
  90. Hewlett & Anderson 1962, pp. 480–481.
  91. Zeilig, Martin (August/September 1995). "Louis Slotin And 'The Invisible Killer'". pp. 20–27. http://www.mphpa.org/classic/FH/LA/Louis_Slotin_1.htm. Retrieved 28 April 2008. 
  92. 92.0 92.1 Hewlett & Anderson 1962, pp. 580–581.
  93. Jones 1985, p. 596.
  94. Hewlett & Anderson 1962, p. 641.
  95. Jones 1985, p. 600.

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