The Manhattan Project was the largest secret industrial enterprise ever undertaken by the United States. Launched in 1942 under the Army Corps of Engineers, it employed more than 130,000 people at its peak, cost about $2 billion in 1940s dollars, and produced the first nuclear weapons ever used in war — the uranium bomb dropped on Hiroshima on August 6, 1945 and the plutonium bomb dropped on Nagasaki on August 9, 1945. The project’s name was itself a cover, drawn from a New York City office that had nothing to do with the work.
The name was a cover. The “Manhattan Engineer District” was a New York City office, far from the real work in Tennessee, Washington State, New Mexico, and Chicago. Secrecy was the project’s organizing principle: each worker was told only what was needed for their specific task. See the full story of the Manhattan Project.
The project had three main lines. At Oak Ridge, Tennessee, engineers built gaseous-diffusion and electromagnetic separation plants to produce uranium enriched in the fissile isotope U-235. At Hanford, Washington, plutonium-production reactors irradiated uranium fuel, and chemical plants separated the new element. At Los Alamos, New Mexico, J. Robert Oppenheimer’s team designed the implosion mechanism that made a plutonium bomb possible and refined the simpler gun-type design for the uranium bomb.
The project succeeded on a wartime clock. Fermi’s first controlled chain reaction came on December 2, 1942 at Chicago Pile-1. Trinity, the first detonation, came on July 16, 1945. Combat use followed less than a month later. For a nuclear program of equivalent ambition in peacetime, the comparable timeline would be measured in decades, not years. The Manhattan Project’s speed was a function of two things usually in short supply in peacetime government: an unlimited budget and a deadline. The post-1945 institutions of American nuclear weapons, energy, and research all trace their origin to the wartime mobilization the project represented.