The Manhattan Project: Making the Atomic Bomb

The McMahon Bill

As support for the May-Johnson bill eroded in late 1945, President Truman withdrew his support. Vandenberg's attempt to establish a joint House- Senate special committee failed, but Brien McMahon of Connecticut successfully created and became chair of the Senate's Special Committee on Atomic Energy. Daily hearings took place until December 20, when McMahon introduced a substitute to the May-Johnson bill. Hearings on the new McMahon bill began in January. Groves opposed McMahon's bill, citing weak security provisions, the low military presence, and the stipulation that commission members be full-time (Groves thought that more eminent commissioners could be obtained if work was part-time). Groves also objected to the bill's provision that atomic weapons be held in civilian rather than military custody. Nevertheless, the Senate approved the McMahon bill on June 1, 1946, and the House approved it on July 20, with a subsequent conference committee eliminating most substantive amendments. The sometimes bitter debate between those who advocated continued military stewardship of America's atomic arsenal and those who saw continued military control as inimical to American traditions ended in victory for supporters of civilian authority. President Truman signed the McMahon Act, known officially as the Atomic Energy Act of 1946, on August 1. The bill called for the transfer of authority from the United States Army to the United States Atomic Energy Commission, a five-member civilian board serving full-time and assisted by a general advisory committee and a military liaison committee.⁶⁶ The Atomic Energy Act entrusted the Atomic Energy Commission with the government monopoly in the field of atomic research and development previously held by its wartime predecessor. ⁶⁷

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