<P> Production of such materials at industrial scale had to be solved for nuclear power generation and weapons production to be accomplished . Up to 1940, the total amount of uranium metal produced in the USA was not more than a few grams, and even this was of doubtful purity; of metallic beryllium not more than a few kilograms; and concentrated deuterium oxide (heavy water) not more than a few kilograms . Finally, carbon had never been produced in quantity with anything like the purity required of a moderator . </P> <P> The problem of producing large amounts of high purity uranium was solved by Frank Spedding using the thermite or "Ames" process . Ames Laboratory was established in 1942 to produce the large amounts of natural (unenriched) uranium metal that would be necessary for the research to come . The critical nuclear chain - reaction success of the Chicago Pile - 1 (December 2, 1942) which used unenriched (natural) uranium, like all of the atomic "piles" which produced the plutonium for the atomic bomb, was also due specifically to Szilard's realization that very pure graphite could be used for the moderator of even natural uranium "piles". In wartime Germany, failure to appreciate the qualities of very pure graphite led to reactor designs dependent on heavy water, which in turn was denied the Germans by Allied attacks in Norway, where heavy water was produced . These difficulties--among many others--prevented the Nazis from building a nuclear reactor capable of criticality during the war, although they never put as much effort as the United States into nuclear research, focusing on other technologies (see German nuclear energy project for more details). </P> <P> In the United States, an all - out effort for making atomic weapons was begun in late 1942 . This work was taken over by the U.S. Army Corps of Engineers in 1943, and known as the Manhattan Engineer District . The top - secret Manhattan Project, as it was colloquially known, was led by General Leslie R. Groves . Among the project's dozens of sites were: Hanford Site in Washington state, which had the first industrial - scale nuclear reactors; Oak Ridge, Tennessee, which was primarily concerned with uranium enrichment; and Los Alamos, in New Mexico, which was the scientific hub for research on bomb development and design . Other sites, notably the Berkeley Radiation Laboratory and the Metallurgical Laboratory at the University of Chicago, played important contributing roles . Overall scientific direction of the project was managed by the physicist J. Robert Oppenheimer . </P> <P> In July 1945, the first atomic explosive device, dubbed "Trinity", was detonated in the New Mexico desert . It was fueled by plutonium created at Hanford . In August 1945, two more atomic devices--"Little Boy", a uranium - 235 bomb, and "Fat Man", a plutonium bomb--were used against the Japanese cities of Hiroshima and Nagasaki . </P>

Which is a characteristic of nuclear fusion but not nuclear fission