The Manhattan Project was a research and development undertaking during World War II that produced the first nuclear weapons. It was led by the United States with the support of the United Kingdom and Canada.

From 1942 to 1946, the project was under the direction of Major General Leslie Groves of the U.S. Army Corps of Engineers. Nuclear physicist Robert Oppenheimer was the director of the Los Alamos Laboratory that designed the actual bombs.

In 1939, Einstein wrote to U.S. President Franklin Roosevelt to warn him that the Nazis were working on a new and powerful weapon: an atomic bomb. Fellow physicist Leo Szilard urged Einstein to send the letter and helped him draft it.

In July 1940, the U.S. Army Intelligence office denied Einstein the security clearance needed to work on the Manhattan Project. The hundreds of scientists on the project were forbidden from consulting with Einstein, because the left-leaning political activist was deemed a potential security risk.

Although he never worked directly on the atomic bomb, Einstein is often incorrectly associated with the advent of nuclear weapons. His famous equation E=mc2 explains the energy released in an atomic bomb but doesn't explain how to build one.

He repeatedly reminded people, "I do not consider myself the father of the release of atomic energy. My part in it was quite indirect."

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