|In July of 1941, Vannevar Bush and James
Conant, new head of the National Defense Research Committee, received
a copy of a draft report from their liaison office in London.
The report, prepared by a group codenamed the MAUD committee and set
up by the British in the spring of 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 that size could be loaded on existing aircraft
and be ready in approximately two years.
American scientists had been in contact with the
MAUD Committee since the fall of 1940, but it was the July 1941 MAUD
report that helped crystallize the American bomb effort. Here
were specific plans for producing a bomb, produced by a distinguished
group of scientists with high credibility in the United States.
The MAUD report dismissed plutonium production,
thermal diffusion, the electromagnetic method, and the centrifuge and
recommended 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 effect 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 the spring of
1940 a large part of the Kaiser Wilhelm Institute in Berlin had been
set aside for uranium research.
Bush and Conant immediately went to work.
After strengthening the Uranium Committee, particularly with the
addition of Enrico Fermi as head of theoretical studies and Harold
Urey as head of isotope separation and heavy water research (heavy
water was still highly regarded as a moderator), Bush asked yet
another reconstituted National Academy of Sciences committee to
evaluate the uranium program. This time he gave Arthur Compton
of the University of Chicago specific instructions to address the
technical questions of critical mass and destructive capability,
partially to verify the MAUD results.
Note: Portions taken from "The Manhattan
Project - Making the Atomic Bomb"; U. S. Dept. of Energy; January