Manhattan Project

Manhattan Project explained

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.

Learn more about the three sites that powered the Manhattan Project

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.

Visualize what happens to atoms during nuclear fission and how the process produces energy

Nuclear fission occurs when an unstable, often massive, atomic nucleus splits into smaller ones—daughter atoms—and releases energy. Within a nuclear reactor, these daughter atoms can collide and combine with neighboring atoms, destabilizing them and triggering a chain reaction of atomic splitting.

Einstein warned the president that splitting atoms could lead to powerful bombs

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.

Meet the the scientists of the Manhattan Project

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.

Building the first atomic bomb required unprecedented coordination

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.

The Manhattan Project employed hundreds of thousands of workers across the US

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.

The first atomic bomb used in war destroyed much of the Japanese city of Hiroshima

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.

The Manhattan Project was one of the most expensive undertakings of World War II

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.

How many people died in the atomic bombings remains disputed

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.