Video: 'Energie atomique : Albert Einstein; Dr. Leo Szilard'

(Wednesday, August 2, 1939) — German-born theoretical physicist Albert Einstein signed a letter today written by Hungarian-German-American physicist and inventor Leo Szilard and addressed to U.S. President Franklin D. Roosevelt, warning that Nazi Germany might develop an atomic weapon and suggesting that the United States should start its own nuclear program.

Video: 'Oppenheimer, Fermi, and Einstein Urge Roosevelt to Commence the Manhattan Project'

The letter, which was delivered to Roosevelt at the White House on Oct. 11, 1939, would prompt FDR to take action and eventually result in the Manhattan Project, which developed the first atomic bombs.