The Manhattan Project, An Interactive History Home The Manhattan Project, An Interactive History Home Department of Energy Home Office of History and Heritage Resources Home DOEHome
J.R. Oppenheimer and General Groves
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Time Periods

1890s-1939:
Atomic Discoveries

1939-1942:
Early
Government Support

1942:
Difficult
Choices

1942-1944:
The Uranium
Path to
the Bomb

1942-1944:
The Plutonium
Path to
the Bomb

1942-1945:
Bringing It All Together

1945:
Dawn of the
Atomic Era

1945-present:
Postscript --
The Nuclear Age


Y-12 Plant, Oak Ridge, 1944OAK RIDGE AND HANFORD COME THROUGH
(Oak Ridge [Clinton] and Hanford, 1944-1945)
Events > Bringing It All Together, 1942-1945

None of Los Alamos's bomb design work would be of any use if Oak Ridge or Hanford did not come through with enough uranium-235 or plutonium for at least one bomb.  Spending on the Manhattan Project reached $100 million per month by mid-1944, yet it was still far from clear that enough of either fissionable substance could be produced before war's end.  In the summer of 1944, Oak Ridge's Y-12 Electromagnetic Plant (above) was plagued by operational problems, and the ongoing barrier crisis at the K-25 Gaseous Diffusion Plant threatened to render it useless.  At Hanford, the first production reactor had not yet been completed.  In addition, officials feared that not enough of the uranium-containing slugs to feed the pile would be available.  Even assuming that enough uranium or plutonium could be delivered by Oak Ridge or Hanford, there was no guarantee that the Los Alamos laboratory would be able to design and fabricate weapons in time.  Only the most optimistic in the Manhattan Project would have predicted, as Groves did when he met with Marshall in August of 1944, that a bomb or bombs powerful enough to make a difference in the current war would be ready by August 1, 1945.  

Electromagnetic method for the enrichment of uraniumDuring the winter of 1944-45, substantial progress was made on uranium enrichment at Oak Ridge thanks to improved performance at each of the major production facilities.  The increase in output also had a lot to do with Kenneth Nichols's work in coordinating a complicated feed schedule for the various plants.  As each of the three main processes -- electromagnetic (Y-12), thermal diffusion (S-50), and gaseous diffusion (K-25) -- came on line, they were used in tandem, with the slightly enriched output from S-50 and K-25 ending up in Y-12 for final processing.  At Y-12, the nine Alpha and four Beta racetracks, while not producing up to design potential, were becoming significantly more reliableLiquid thermal diffusion method for the enrichment of uranium. because of maintenance improvements and chemical refinements introduced by Tennessee Eastman.  The S-50 Thermal Diffusion Plant being built by the H. K. Ferguson Company was almost complete and was already producing small amounts of enriched material in the finished racks. The K-25 Gaseous Diffusion Plant, complete with barriers, was undergoing final leak tests.  By March 1945, Union Carbide had worked out most of the kinks in K-25 and had started recycling uranium hexafluoride through the system.  S-50 was finished at the same time that the Y-12 racetracks were demonstrating increased efficiency.  The Beta calutrons at the electromagnetic plant were producing weapon-grade uranium-235 using feed from the modified Alpha racetracks and the small output from the gaseous diffusion and thermal diffusion facilities.  Oak Ridge was now sending enough enriched uranium-235 to Los Alamos to meet experimental needs. 

Gaseous diffusion method for the enrichment of uraniumTo increase production, Groves proposed an additional gaseous diffusion plant (K-27) for low-level enrichment and a fourth Beta building containing two racetracks for high-level enrichment, both facilities to be completed by February 1946, in time to contribute to the war against Japan, which many thought would not end before summer 1946.  In short, by spring 1945 uranium enrichment was still an enormously complicated and laborious process, but it was clearly on the right track.  "Little Boy" (right), the atomic bomb dropped on the Japanese city of Hiroshima on August 6, 1945, contained uranium that had been enriched at Oak Ridge.  The uranium path to the atomic bomb had indeed been proven viable and short enough to result in a weapon before war's end.  

Construction of B Reactor, HanfordAt Hanford, B Reactor was completed and began functioning in September 1944.  Although an unexpected problem with xenon poisoning caused a delay of several months, by early February 1945 the first plutonium produced at B was on its way to Los Alamos.  In December 1944, D Reactor first went critical, and the third and final reactor, F, began operation in February 1945.  The amount of plutonium shipped to Los Alamos grew rapidly over the spring and summer.  From April to May alone, plutonium production increased five-fold.  June production was even better, as was July.  By the end of August 1945, three plutonium devices had been constructed at Los Alamos -- and two had already been detonated, including one over the Japanese city of Nagasaki.  The plutonium path to the bomb had proven equally effective as the uranium one.

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Sources and notes for this page.

The text for this page was adapted from, and portions were taken directly from the Office of History and Heritage Resources publication: F. G. Gosling, The Manhattan Project: Making the Atomic Bomb (DOE/MA-0001; Washington: History Division, Department of Energy, January 1999), 40-42.  See also the History Office publication: Richard G. Hewlett and Oscar E. Anderson, Jr., The New World, 1939-1946: Volume I, A History of the United States Atomic Energy Commission (Washington: U.S. Atomic Energy Commission, 1972), 294-310, 374.  Four devices were completed by the end of August 1945: 1) the implosion-type plutonium device tested on July 16, 1945, at the Trinity Site; 2) the gun-type uranium bomb ("Little Boy") detonated over Hiroshima on August 6, 1945; 3) the implosion-type plutonium bomb ("Fat Man") dropped on Nagasaki on August 9, 1945; and 4) a fourth bomb, also an implosion-type plutonium device, which Leslie Groves reported to the War Department would be available for use in the war by about August 24.  For more on the number and design of nuclear weapons available following the end of the war, see "The Manhattan Engineer District, 1945-1946."  The photograph of the Y-12 complex at Oak Ridge is courtesy the Lawrence Berkeley National Laboratory.  The three diagrams illustrating methods of uranium enrichment are reproduced from the Department of Energy report Linking Legacies: Connecting the Cold War Nuclear Weapons Production Processes to their Environmental Consequences (Washington: Center for Environmental Management Information, Department of Energy, January 1997), 138.  The photograph of B Reactor under construction is courtesy the Hanford Site.

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