On August 13, 1942, the Manhattan Engineer District, whose name was based upon the geographical location of its headquarters, was established . In September, the Army appointed Colonel Leslie R. Groves to head the effort. Groves held that the exigencies of war required scientists to move from laboratory research to development and production in record time. Though traditional scientific caution might be short-circuited in the process, there was no alternative if a bomb was to be built in time to be used in the current conflict (World War II).
Various isotope separation methods (uranium enrichment ) to produce uranium-235 were being researched at this time. One was gaseous diffusion being done at Columbia and another was the electromagnetic method being done at Berkeley under Ernest O. Lawrence . Based upon the success of the electromagnetic method, the S-1 (The Office of Scientific Research and Development Section On Uranium) Executive Committee recommended building plants in Tennessee at Site X  (now Oak Ridge).
During this time, construction was taking place on the Stagg Field pile -- CP-1  (Chicago Pile Number one) at the Metallurgical Laboratory in Chicago where Enrico Fermi  was conducting his research on chain reactions . Also occurring was Glenn Seaborg 's inventive work with plutonium, particularly his investigations on plutonium's oxidation states that seemed to provide a way to separate plutonium from the irradiated uranium to be produced in the pile. In August, his team produced a microscopic sample of pure plutonium , a major chemical achievement and one fully justifying future work on the pile.
Theoretical studies in fission research and instrument and measurement studies, led by Robert Oppenheimer and including Felix Bloch , Hans Bethe , and Edward Teller , were also influencing the decisions being made in the effort to build the bomb. Additionally, a significant event occurred at CP-1 on December 2, 1942, when the massive lattice pile of 400 tons of graphite, six tons of uranium metal, and fifty tons of uranium oxide achieved the first self-sustaining chain reaction . [For more information, see the Neutronic Reactor patent  and related article ]
On December 28, 1942, President F. D. Roosevelt approved the authorization for the Manhattan Project to build full-scale gaseous diffusion, plutonium, and electromagnetic plants. With this, all the pieces were being put into place to begin the operations of the Manhattan Project .
- Edited excerpts from The Manhattan Project: Making the Atomic Bomb 
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