The secret American-led scientific and industrial program that built the first nuclear weapons during the Second World War — mobilizing over 130,000 people, spending two billion dollars, and producing the bombs dropped on Hiroshima and Nagasaki in August 1945, opening the nuclear age and permanently changing the relationship between science, the state, and mass destruction.
The Manhattan Project employed more people than the American automobile industry, cost more than the entire prewar US defense budget, and was kept secret from Congress, most cabinet members, and the Vice President. The scientists who built the bomb included a dozen future Nobel laureates who had fled Hitler. The decision to use it was made by a committee in six weeks. The weapons killed at least 110,000 people instantly. And no nuclear weapon has been used in war since.