Manhattan Project: The Manhattan Engineer District, 1945-1946

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

(Unofficial) MED emblem, 1946 THE MANHATTAN ENGINEER DISTRICT
(1945-1946)
Events > Postscript -- The Nuclear Age, 1945-Present

With the end of the Second World War, American policymakers anticipated that the Manhattan Project’s infrastructure would be turned over to and managed by a largely civilian commission. General Leslie Groves initially thought this would happen soon after the ending of hostilities. His strategy for interim management of the complex was thus one of "hold the line," where he sought to maintain the essential soundness of the physical plant and the personnel that ran it, complete ongoing construction, and promote efficiency and economy. One of his first decisions was to close down marginal operations such as the S-50 Thermal Diffusion Plant in the K-25 area and the Alpha racetracks of the Y-12 electromagnetic separations plant at Oak Ridge. His most serious short-term problem was in retaining personnel, particularly at Los Alamos where many scientists and technicians were eager to return to civilian pursuits.

By early 1946, Groves realized that the Manhattan Engineer District’s trusteeship of the complex might last for an extended period of time. He decided to abandon the hold-the-line policy and begin making longer range plans for the complex, even though this might restrict the freedom of action for any future commission. Expiring operating contracts at major sites demanded his immediate attention. He negotiated extensions through mid-1947 for all of the contracts except for at Hanford, where the DuPont Corporation was determined to withdraw. Groves turned to the General Electric Company, which agreed to replace DuPont. As part of the new contract to operate Hanford, General Electric would also construct and operate a government-owned laboratory at Knolls, a site five miles from the company’s home plant at Schenectady, New York. The laboratory would allow General Electric to pursue the development of atomic power.

With morale and personnel loss continuing to be problems at Los Alamos, Groves upgraded living conditions at the site with major improvements in utilities, housing, and community facilities. He also sought to focus the laboratory more on weapons development by relocating various weapons production and assembly activities away from Los Alamos. Already at the close of the war, the engineering group of the laboratory’s ordnance division began consolidating weapons assembly functions at Sandia Base on the old Albuquerque, New Mexico, airport. Groves now added a special Army battalion at Sandia to take charge of surveillance, field tests, and weapons assembly. In addition, he negotiated an agreement with Monsanto for the development and manufacture at its plant in Dayton, Ohio, of weapons components previously fabricated at Los Alamos.

Groves also attempted to prevent the disintegration of the nationwide nuclear research organization that had been built up during the war. Upon the advice of the Advisory Committee on Research and Development that he set up, Groves initiated the national laboratories system that would conduct unclassified fundamental research requiring equipment too expensive for the academic or private sector laboratories to afford. In April 1946, the University of Chicago agreed to operate the new Argonne National Laboratory formed from the existing Metallurgical and Argonne laboratories. In July, nine northeastern universities banded together to operate the Brookhaven National Laboratory located at an old Army camp on Long Island, New York.

Problems in the weapons complex nonetheless continued to mount. At Hanford, the three production reactors began to show signs of wear. Sustained operation had caused expansion of the graphite core of each reactor, resulting in distortion of the aluminum tubes containing the uranium slugs and through which the cooling water flowed. With limited operating experience, scientists and engineers feared the graphite expansion would continue and render all three reactors inoperable. Potential loss of polonium production was the most immediate concern. Polonium was used as a neutron source for initiating the chain reaction in the plutonium device, and, given polonium’s half-life of only 138 days, production stoppage could make existing weapons useless in a matter of months. As a result, the Army in March 1946 placed B reactor in standby and significantly curtailed power levels on D and F reactors in an effort to conserve their useful lives.

Loss of plutonium production was perhaps less critical due to ongoing problems at the Los Alamos laboratory. With low morale and lack of direction causing many scientists experienced in weapons fabrication to leave the laboratory, the Army concluded that Los Alamos had lost, at least temporarily, the capability to keep the more complex implosion weapon, which used plutonium, in a ready state for use in the event of war. As an interim measure, the Army authorized concentrated production on the gun-type weapon used at Hiroshima. The gun method was highly wasteful of uranium-235, but this drawback was somewhat offset by advances in the gaseous diffusion isotope separations process. The Oak Ridge gaseous diffusion plants, with the new K-27 plant being tied into K-25 in February 1946 to form one continuous operation, over time had achieved stable production rates at very high efficiencies.

Despite Groves’s best efforts, the Manhattan Project complex suffered in the aftermath of the war. By early 1947, the nation’s atomic energy establishment amounted to little more than the remnants of the military organization and facilities that had produced the world’s first atomic weapons.

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Sources and notes for this page.

The text for this page was adapted in part from, and portions were taken directly from the Office of History and Heritage Resources publications: F. G. Gosling, The Manhattan Project: Making the Atomic Bomb (DOE/MA-0001; Washington: History Division, Department of Energy, January 1999), 55; and 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), 301-302, 624-637, 646, and Hewlett and Francis Duncan, Atomic Shield, 1947-1952, Volume II, A History of the United States Atomic Energy Commission (University Park, PA: Pennsylvania State University Press, 1969), p. xiii. Also used were Vincent C. Jones, Manhattan: The Army and the Atomic Bomb, United States Army in World War II (Washington: Center of Military History, United States Army, 1988), 579-596; Rodney P. Carlisle with Joan M. Zenzen, Supplying the Nuclear Arsenal: American Production Reactors, 1942-1992 (Baltimore: The Johns Hopkins University Press, 1996), 55-56, and AEC Staff Paper 1140, History of Expansion of AEC Production Facilities, August 16, 1963, box 1435, folder I&P 14, History, 1958-1966 Secretariat files, DOE Historical Research Center. The (unofficial) MED emblem is ca. 1946; it is reprinted in Jones, Manhattan, 89. The photograph of the Sandia security gate is courtesy the Sandia National Laboratories. Click here for information on the aerial photograph of Hanford. The photograph of Little Boy is courtesy the U.S. Army Corps of Engineers (via the National Archives).