The Manhattan Project was a top-secret US government program that developed the world’s first atomic weapons. In 1938, scientists in Germany discovered nuclear fission—the splitting of an atom that releases enormous energy.
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Driven by fears of a Nazi nuclear bomb, the Manhattan Project united leading scientists to build the first atomic weapons. Its success ended World War II, caused catastrophic human loss, and launched the nuclear age that reshaped global politics and science.
The Manhattan Project relied on three main sites: Oak Ridge, which enriched uranium; Hanford, which produced plutonium in large reactors; and Los Alamos, which designed and assembled the bombs—work that culminated in the Trinity nuclear test in 1945.
Nuclear fission occurs when a heavy atom is split into smaller atoms, releasing energy and triggering chain reactions. This short PBS NOVA video uses simple demonstrations to show how fission works and why it’s so powerful.
In a 1939 letter to Franklin D. Roosevelt, Albert Einstein explained that nuclear fission could produce immense energy—and devastating weapons. The warning helped spur the Manhattan Project, a role Einstein later deeply regretted.
This resource profiles the scientists behind the Manhattan Project—from Nobel laureates like Fermi and Bethe to controversial figures like Teller and Fuchs—showing how their ideas, rivalries, and choices shaped the development of the atomic age.
Creating the first atomic bombs demanded breakthroughs in physics, engineering, and logistics—uniting elite scientists with tens of thousands of workers across the US. This in-depth history explains how the Manhattan Project overcame those challenges.
Between 1942 and 1945, the Manhattan Project relied on a vast workforce spread across secret sites. They performed roles ranging from scientific research to manual labor, motivated by patriotism, opportunity, secrecy, and wartime necessity.
On August 6, 1945, the Enola Gay dropped the Little Boy atomic bomb on Hiroshima—the first combat use of a nuclear weapon. It leveled five square miles and killed tens of thousands, with accounts from both American and Japanese witnesses.
Building the first atomic weapons required hundreds of thousands of workers, vast secret facilities, and enormous spending. This 1998 study details the full cost of the Manhattan Project and compares it to other major US wartime expenditures.
Nearly 80 years after Hiroshima and Nagasaki, historians still disagree on the death toll from the atomic bombings. Estimates vary by up to 100,000, reflecting differences in methodology, sources, and the method used to count later radiation-related deaths.
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