The Manhattan Project was started in 1939 by the US Government to explore the military potential of uranium. The knowledge that the Germans were working on nuclear weapons research at the same time spurred the creation of the program. It started with a modest budget and a small group of researchers. In the meantime, Brittan was also pursuing nuclear research and verified in 1939 that fifty pounds of uranium could be made into a bomb that could be carried in a conventional bomber.
World War II began in 1939 with the German invasion of Poland. Brittan created their own atomic bomb project in 1940. Information on their research was forwarded to the United States. Having received no reaction to their information, a member of the project flew to the United States and visited physicists doing nuclear research.
In 1941, the President moved forward to create a major project dedicated to creating an atomic bomb as quickly as possible. The attack on Pearl Harbor in December of 1941 and the declaration of war with Japan and Germany added urgency to the project. The Manhattan Project was charged in 1942 with the task of developing the infrastructure necessary to building an atomic bomb.
Millions of dollars were allocated and the project was carried out at a number of different sites around the United States. The first major problem that had to be solved was how to separate the U-235 isotope from uranium ore which consisted mostly of U-238. Three different techniques were pursued. Research was also done on the newly discovered radioactive element plutonium as a possible alternative to U-235. Finally, graphite was investigated as a possible moderator to control nuclear chain reactions. The Germans were also working on graphite moderation but their graphite rods contained boron which reduced their effectiveness. U.S. researchers created rods without boron and they worked as expected to control the reaction.
Many physicists worked on theoretical problems of neutron diffusion and possible designs for an atomic bomb. The main approach was to create a sphere of U-235 which would exceed the critical mass and result in an explosion. The problem was how to arrange the parts of the bomb so that the sphere was created when the bomb was triggered. One idea was to shoot a plug into a subcritical sphere. Another was to use shaped charges to slam segments of a sphere together. When the critical mass was achieved, a runaway chain reaction in the U-235 would cause it to fission, creating a huge explosion.
Physicist Edward Teller proposed a more powerful nuclear bomb which he called a hydrogen bomb. His idea was to use an atomic bomb as a trigger to cause deuterium and tritium to undergo nuclear fusion. The resulting explosion would be much more powerful than that atomic trigger. Teller pushed hard to build such a bomb but all his proposals were turned down in favor of creating a fission bomb.
