In this letter Albert Einstein advises President Franklin D. Roosevelt of developments in the field of nuclear energy, particularly the possibility that foreign governments might harness a uranium-based nuclear chain reaction to create a weapon, and recommending quick action by the Roosevelt administration to advance American nuclear research. This letter was a collaboration between Einstein, physicist Leo Szilard, and economist Alexander Sachs, who had been an administrator of the National Recovery Administration and Roosevelt adviser. Sachs personally delivered the letter to Roosevelt on October 11, 1939. The outbreak of World War II on September 1, 1939 had delayed the delivery. This letter is credited with launching what would eventually become known as the Manhattan Project.