#4 Manhattan Project

In parallel with the work on uranium was an effort to produce plutonium. After the feasibility of the world's first artificial nuclear reactor was demonstrated in Chicago at the Metallurgical Laboratory, it designed the X-10 Graphite Reactor at Oak Ridge and the production reactors in Hanford, Washington, in which uranium was irradiated and transmuted into plutonium. The plutonium was then chemically separated from the uranium, using the bismuth phosphate process. The Fat Man plutonium implosion-type weapon was developed in a concerted design and development effort by the Los Alamos Laboratory.