The Manhattan Project

In 1939, the Nazis were rumored to be developing an atomic bomb. The United States initiated its own program under the Army Corps of Engineers in June 1942. America needed to build an atomic weapon before Germany or Japan did.

General Leslie R. Groves, Deputy Chief of Construction of the U.S. Army Corps of Engineers, was appointed to direct this top-secret project.

General Leslie R. Groves
(1896-1970)

General Leslie R. Groves directed the Manhattan Project. More

University of Chicago

Meanwhile, experiments in a small laboratory beneath the University of Chicago's abandoned Stagg Field were expanding understanding of atomic theory. The first controlled nuclear reaction occurred under Stagg Field. More

Oak Ridge, Tennessee

Scientists now had to create the fuel for an atomic bomb. The Oak Ridge facility separated the nuclear fuel U-235 from U-238, natural uranium. More

Hanford, Washington

The Hanford Engineer Works produced plutonium. More

Los Alamos, New Mexico

At Los Alamos, an international team of scientists and engineers labored around the clock to create the first atomic weapons. More

• Uranium Fission
  1938
  Otto Hahan and Fritz Strassmann's discovery of fission steered Germany toward developing an atomic weapon. This motivated the U.S. to launch the Manhattan Project.
• The Race for the Atomic Bomb Begins
  1939-1941
  World War II started September 1, 1939, when Germany attacked Poland. By 1941, the Germans were leading the race for the atomic bomb. They had a heavy-water plant, high-grade uranium compounds, a nearly complete cyclotron, capable scientists and engineers, and the greatest chemical engineering industry in the world.
• The Research Effort Struggles
  1941-1945
  Factors including internal struggles, a major scientific error, and the devastation of total war compromised any successful research toward a German atom bomb. Unlike the American program, the Germans never had a clear mission under continuously unified leadership.
• The First Controlled Nuclear Reaction
  1942
  At the University of Chicago reactor, Enrico Fermi oversaw the first controlled energy release from the nucleus of the atom.
• U-235 Output Begins
  1945
  After intense effort, the Y-12 plant in Oak Ridge, Tenn., began to produce bomb-grade U-235, which was shipped to Los Alamos, N.M. U-235 was used in the Little Boy bomb and plutonium was used in the Fat Man bomb produced at Los Alamos.