The Einstein–Szilárd letter was a letter sent to United States President Franklin D. Roosevelt on August 2, 1939, that was signed by Albert Einstein but largely written by Leó Szilárd in consultation with fellow Hungarian physicists Edward Teller and Eugene Wigner. The letter advised Roosevelt that Nazi Germany might be researching the use of nuclear fission to create atomic bombs and suggested that the U.S. should begin studying the possibility itself.
The letter warned that:
In the course of the last four months it has been made probable — through the work of [Frédéric] Joliot[-Curie] in France as well as [Enrico] Fermi and Szilard in America — that it may become possible to set up a nuclear chain reaction in a large mass of uranium, by which vast amounts of power and large quantities of new radium-like elements would be generated. Now it appears almost certain that this could be achieved in the immediate future.
This new phenomenon would also lead to the construction of bombs, and it is conceivable — though much less certain — that extremely powerful bombs of a new type may thus be constructed. A single bomb of this type, carried by boat and exploded in a port, might very well destroy the whole port together with some of the surrounding territory. However, such bombs might very well prove to be too heavy for transportation by air.
The letter was signed by Einstein on August 2 and delivered to Roosevelt by economist Alexander Sachs. But Sachs was delayed until October 11 because of the president's preoccupation with Adolf Hitler's invasion of Poland, which had started World War II. After hearing Sachs' summary of the letter, Roosevelt authorized the creation of the Advisory Committee on Uranium. The Committee first met on October 21 and was headed by Lyman James Briggs, Director of the National Bureau of Standards. Six thousand dollars were budgeted for neutron experiments performed by Fermi at the University of Chicago.
The letter has often been seen as the origin of the Manhattan Project, the successful wartime nuclear weapons project which produced the bombs that were dropped on Hiroshima and Nagasaki in 1945. The path from the letter to the bombings though is considerably longer than just this: the Advisory Committee on Uranium did not vigorously pursue the development of a weapon, and at least two other organizations superseded it (the National Defense Research Committee and the Office of Scientific Research and Development) before the work of fission research was finally superseded by the Manhattan Engineering District in 1942 and became a full-scale bomb development program.