Otto Frisch and Rudolf Peierls
"I have often been asked why I didn't abandon the project there and then, saying nothing to anybody. Why start on a project which, if it was successful, would end with the production of a weapon of unparalleled violence, a weapon of mass destruction such as the world had never seen? The answer is very simple. We were at war, and the idea was reasonably obvious; very probably some German scientists had had the same idea and were working on it". - Otto Frisch; Refugee Physicist whose work with Rudolf Peierls formed the basis of the MAUD report .
Otto Frisch 
Frisch was born in Vienna, Austria in 1904. He received a doctorate in physics in 1926 from the University of Vienna. After fleeing Nazi Germany in 1933, Frisch worked with Niels Bohr at the Institute of Theoretical Physics in Copenhagen. In 1939 Frisch and his aunt Lise Meitner wrote a paper explaining the theory of uranium fission, in which they argued that a few pounds of uranium could create the explosive and destructive power of thousands of pounds of dynamite by splitting the atom. In 1940, he and Rudolf Peierls penned a memorandum to the British government explaining the idea of a uranium fission bomb. Among many other well-respected positions Frisch held, he was the head of the Critical Assembly Group for the Manhattan project from 1943-1946.
Rudolf Peierls 
Peierls was born in Berlin, Germany in 1907. He studied nuclear physics under respected physicists Werner Heisenberg and Wolfgang Pauli in Berlin, Munich, Zurich, and Leipzig. In 1929, he conceived the theory of positive carriers to explain the thermal and electrical conductivity behaviors of semiconductors. Peierls moved to England and found a job at Birmingham University when Hitler came to power in Germany. He started studying atomic physics, and soon teamed up with Otto Frisch to address the British government about the feasibility of an atomic bomb based on uranium fission. Peierls started work on the Manhattan Project in 1943, and after the war, he taught at Birmingham University, and Oxford University.
After Hahn and Strassmann discovered uranium fission, Otto Frisch and his aunt Lise Meitner conducted some critical experiments involving the fast fission of uranium 235. In 1940, Frisch met up with Rudolf Peierls, and they conceived one of the most significant documents of the twentieth century. Originally named the “Memorandum on the properties of the radioactive “super-bomb”,” they argued that if the rare isotope uranium 235 (0.7% naturally occurring) could be extracted from naturally occurring uranium 238, the amount needed for an atomic bomb could be measured in kilograms rather than the early estimates of tons. Frisch and Peierls believed that if the fissile (slow thermal neutrons capable of causing a fission) component of the weapon was made in two parts, each less than the critical mass, the atomic bomb could be set off simply by rapidly bringing the two parts together. As part of their memorandum read, “…The energy liberated by a 5kg bomb would be equivalent to…several thousand tons of dynamite…” .
Interestingly, most of the experimental and theoretical scientific calculations and assessments that formed the basis for the MAUD Report were the work of Otto Frisch and Rudolf Peierls. However, since they were both Germans living in England, they were “officially classified as “enemy aliens”, and could not, by law, be part of a wartime committee . The name MAUD was a code name chosen from the first name of one of the member’s nanny. The MAUD committee worked out the basic principles of both the fission bomb design and uranium enrichment by gaseous diffusion. The work completed by this top-secret committee alerted the United States to the feasibility of an atomic bomb. In July 1941, the MAUD committee issued an eye-catching report. The report was titled “On the Use of Uranium for a Bomb,” and it reaffirmed that the weapon suggested by Frisch and Peierls would definitely work. Since the bomb only required approximately a ten-kilogram critical mass, and could fit on existing warplanes, the MAUD report predicted it could be ready by 1943. This report helped crystallize the American bomb effort because it outlined specific plans for producing a bomb, and the report was produced by a distinguished group of well-respected scientists.
 Society for the Historical Preservation of the Manhattan Project. http://www.childrenofthemanhattanproject.org/index.htm. April 4, 2002.
 Spartacus Education. Otto Frisch. http://www.spartacus.schoolnet.co.uk/GERfrisch.htm. April 4, 2002.
 Reinhardt, Joachim. Pictures of Famous Physicists. http://www.th.physik.uni-frankfurt.de/~jr/portraits.html. April 4, 2002.
 Atomic Weapons Establishment (AWE). http://www.awe.co.uk/main_site/about_awe/keeping_the_peace/1940.htm. April 28, 2002.