J. Robert Oppenheimer Los Alamos Laboratory New Mexico gun-type fission weapon Little Boy implosion-type nuclear weapon Fat Man plutonium-239 uranium-235 Manhattan Project plutonium
The work of the Manhattan Project took place at dozens of sites across the United States, and even some outside of its borders. It would ultimately cost over US$2 billion (equivalent to about $24 billion in 2021) and employ over 125,000 people simultaneously at its peak. Groves appointed J. Robert Oppenheimer to organize and head the project's Los Alamos Laboratory in New Mexico, where bomb design work was carried out. Two different types of bombs were eventually developed: a gun-type fission weapon that used uranium-235, called Little Boy, and a more complex implosion-type nuclear weapon that used plutonium-239, called Fat Man.
