Manhattan Project: Final Bomb Design, Los Alamos: Laboratory, 1944-1945

FINAL BOMB DESIGN
(Los Alamos: Laboratory, 1944-1945)
Events > Bringing It All Together, 1942-1945

Late in 1944, Los Alamos began to shift from research to development and bomb production. Increased production at Oak Ridge and Hanford seemed to promise that enough plutonium and enriched uranium would be available for at least one bomb using each. Germany no longer was the intended primary target. The war in Europe (left) appeared to be entering its final phase, and evidence uncovered by the ALSOS mission in November 1944 indicated that the German atomic program had not gone beyond the research phase. Already by summer 1944, Groves and his advisers had turned their sights toward Japan. The atomic bomb would justify the years of effort, including both the vast expenditures and the judgment of everyone responsible, by bringing the war in the Pacific to a fiery end.

Ongoing problems continued to complicate the efforts of Robert Oppenheimer (right) to finalize bomb design. Foremost among these were continuing personnel shortages, particularly of physicists, and supply difficulties. The procurement system, designed to protect the secrecy of the Los Alamos project, led to frustrating delays and, when

Herb Lehr, SED, holding the Gadget's core, July 1945.

combined with persistent late war shortages, proved a constant headache. The lack of contact between the remote laboratory and its supply sources exacerbated the problem, as did the relative lack of experience the academic scientists had with logistical matters. Leslie Groves and James Conant were determined not to let mundane problems compromise the bomb effort, and in fall 1944 they made several changes to prevent this possibility. Conant shipped as many scientists as could be spared from the Met Lab and Oak Ridge to Los Alamos, hired every civilian machinist he could lay his hands on, and arranged for Army enlisted men to supplement the work force (these GIs were known as SEDS ("Special Engineering Detachment"). Hartley Rowe, an experienced industrial engineer, provided help in easing the transition from research to production. Los Alamos also arranged for a rocket research team at the California Institute of Technology to aid in procurement, test fuses, and contribute to component development. These changes kept Los Alamos on track as design work reached its final stages.

Weapon design for the uranium gun-type bomb was frozen in February 1945. Confidence in the weapon was high enough that a test prior to combat use was seen as unnecessary. The design for an implosion device was approved in March with a test of the more problematic plutonium weapon scheduled for July 4. Oppenheimer shifted the laboratory into high gear and assigned Samuel Allison, Robert Bacher, and George Kistiakowsky to the Cowpuncher Committee to "ride herd" on the implosion weapon. He placed Kenneth T. Bainbridge (right) in charge of Project Trinity, a new division to oversee the July test firing. "Deke" Parsons headed Project Alberta, known as Project A, which had the responsibility for preparing and delivering weapons for combat.

Buttons of plutonium metal, Los Alamos, 1945 The bombs had to be physically assembled at Los Alamos, and this depended largely on the ability of the chemists and metallurgists to process the uranium and plutonium into metal and craft them into the correct shape and size. Plutonium (left) posed by far the greater obstacle. It existed in different states, depending upon temperature, and was extremely toxic. Working under intense pressure, the chemists and metallurgists managed to develop precise techniques for processing plutonium just before it arrived in quantity beginning in May.

As a result of progress at Oak Ridge and metallurgical and chemical refinements on plutonium that improved implosion's chances, the nine months between July 1944 and April 1945 saw the American bomb project progress from doubtful to probable. The August 1 delivery date for the "Little Boy" uranium bomb (right) certainly appeared more likely than it had when Groves briefed George Marshall. There would be no implosion weapons in the first half of 1945 as Groves had hoped, but developments in April boded well for the scheduled summer test of the "Fat Man" plutonium bomb. And recent calculations provided by Hans Bethe's theoretical group gave hope that the yield for the first weapon would be in the vicinity of 5,000 tons of TNT rather than the 1,000-ton estimate provided in fall 1944.

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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 publications: F. G. Gosling, The Manhattan Project: Making the Atomic Bomb (DOE/MA-0001; Washington: History Division, Department of Energy, January 1999), 42-43, 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), 253, 321. Click here for information on the animation of the first 0.11 seconds of the explosion. The photograph of "D-Day" is courtesy the National Archives. The photograph of Robert Oppenheimer in front of a blackboard is reproduced by permission of the J. Robert Oppenheimer Memorial Committee. The photograph of SED Herb Lehr holding the Gadget's core is courtesy the Los Alamos National Laboratory (LANL); it is reprinted in Rachel Fermi and Esther Samra, Picturing the Bomb: Photographs from the Secret World of the Manhattan Project (New York: Harry N. Abrams, Inc., Publishers, 1995), 138. The photograph of Kenneth Bainbridge is courtesy LANL. The photograph of the buttons of plutonium metal at Los Alamos in 1945 is courtesy LANL (via the Federation of American Scientists). The photograph of Little Boy is courtesy the U.S. Army Corps of Engineers (via the National Archives).

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