The Manhattan Project was the code name for the United States effort during World War II to produce an atomic device. It was named for the Manhattan Engineer District of the US Army Corps of Engineers, because a lot of the early research was done in New York City. The program was slowly organized after nuclear fission was discovered by German scientists in 1938. Fearing the worst if Germany might produce an atomic device first, Leo Szilard and other scientists asked Albert Einstein to write a letter to President Roosevelt, asking for support to further research the power of nuclear fission. His letters were successful, and President Roosevelt established the Manhattan Project(Feldman,p.212).

Physicists from 1939 onward conducted a lot of research to find answers to such questions as: "How many neutrons were emitted in each fission;" "Which elements would not capture the neutrons, but would reduce their velocity;" and "whether only the lighter and scarcer isotope of uranium (U-235) or the common isotope (U-238) should be used." They learned that each fission releases a few neutrons. A chain reaction was theoretically possible only if not too many neutrons escaped from the mass. To create this chain reaction and turn it into a usable weapon was the ultimate goal of the Manhattan Project(Dickey,p.135).

In 1942 General Leslie Groves was chosen to lead the project. He then purchased a site at Oak Ridge, Tenn., and built facilities to separate the necessary uranium-235 from the much more common uranium-238. Uranium 235 was an optimal choice for the bomb because of its unusually unstable composition. Thus, the race to separate the two began. During that time, the work to perfect the firing mechanism and structure of the bomb was also swiftly underway.

After much difficulty, an absorbent barrier suitable for separating isotopes of uranium was developed and installed in the Oak Ridge gaseous diffusion plant. Finally, in 1945, uranium-235 of bomb purity (90%) was shipped to Los Alamos, where it was fashioned into a gun-type weapon. In a barrel, one piece of uranium was fired at another, together forming an explosive mass(Feinberg,p.15).