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

The first page of the MAUD Report. THE MAUD REPORT
Events > Early Government Support, 1939-1942

The most influential study of the feasibility of the atomic bomb originated on the other side of the Atlantic. In July 1941, just days after finding the second National Academy of Sciences report so disappointing, Vannevar Bush received a copy of a draft report forwarded from the National Defense Research Committee liaison office in London.  The report, prepared by a group codenamed the MAUD Committee and set up by the British in spring 1940 to study the possibility of developing a nuclear weapon, maintained that a sufficiently purified critical mass of uranium-235 could fission even with fast neutrons. Building upon theoretical work on atomic bombs performed by refugee physicists Rudolf Peierls and Otto Frisch in 1940 and 1941, the MAUD report estimated that a critical mass of ten kilograms would be large enough to produce an enormous explosion.   A bomb this size could be loaded on existing aircraft and be ready in approximately two years.

Niels Bohr (The name "MAUD" is strange enough to merit explanation.  Although many people assume MAUD is an acronym of some sort, it actually stems from a simple misunderstanding.  Early in the war, while Niels Bohr (right) was still trapped in German-occupied Denmark, he sent a telegram to his old colleague Frisch.  Bohr ended the telegram with instructions to pass his words along to "Cockroft and Maud Ray Kent."  "Maud," mistakenly thought to be a cryptic reference for something atomic, was chosen as a codename for the committee.  Not until after the war was Maud Ray Kent identified as the former governess of Bohr's children who subsequently moved to England.)

Americans had been in touch with the MAUD Committee since fall 1940, but it was the July 1941 MAUD report that helped the American bomb effort turn the corner.  (Internal British discussions of the MAUD Report also probably first alerted Soviet intelligence to the atomic bomb program.)  The MAUD Report was influential because it contained plans for producing a bomb drawn up by a distinguished group of scientists with high credibility in the United States, not only with Bush and James Conant but with President Roosevelt.  The MAUD report dismissed plutonium production, thermal diffusion, the electromagnetic method, and the centrifuge and called for gaseous diffusion of uranium-235 on a massive scale.  The British believed that uranium research could lead to the production of a bomb in time to affect the outcome of the war.  While the MAUD report provided encouragement to Americans advocating a more extensive uranium research program, it also served as a sobering reminder that fission had been discovered in Nazi Germany almost three years earlier and that since spring 1940 a large part of the Kaiser Wilhelm Institute in Berlin had been set aside for uranium research.

Vannevar Bush and James Conant, Berkeley, 1940 Bush and Conant (right) immediately went to work.  After strengthening the S-1 (Uranium) Committee, particularly with the addition of Enrico Fermi as head of theoretical studies and Harold C. Urey as head of isotope separation and heavy water research (heavy water was highly regarded as a moderator for piles (reactors)), Bush asked yet another reconstituted National Academy of Sciences committee to evaluate the uranium program.  This time he gave Arthur Compton specific instructions to address technical questions of critical mass and destructive capability, partially to verify the MAUD results.

With the MAUD Report and its influence on developments in the United States, the prospects for a wartime atomic bomb had brightened considerably.

Previous    Next

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), 9.  On the credibility the MAUD Committee members had in Washington, see McGeorge Bundy, Danger and Survival: Choices About the Bomb in the First Fifty Years (New York: Random House, 1988), 48-49.  For the origin of the word "MAUD," see the footnote in Dennis C. Fakley, "The British Mission," Los Alamos Science (Winter/Spring 1983), 186.  In addition to the internet version, which is at, the MAUD Report is available on the National Archives microfilm collection M1392, Bush-Conant File Relating to the Development of the Atomic Bomb, 1940-1945 (Washington: National Archives and Records Administration, 1990), reel #1/14.  The photograph of Niels Bohr is courtesy the Fermi National Accelerator Laboratory.  Click here for information on the photograph of Vannevar Bush and James Conant.

Home | History Office | OpenNet | DOE | Privacy and Security Notices
About this Site | How to Navigate this Site | Note on Sources | Site Map | Contact Us