Leo Szilard drafted the letter to President Franklin D. Roosevelt that Albert Einstein signed in 1939.
Szilard, a Hungarian-American physicist, feared that Nazi Germany might develop an atomic weapon after the discovery of nuclear fission. He understood that a chain reaction in uranium could potentially release enormous energy and produce a bomb. With fellow physicists Eugene Wigner and Edward Teller, he sought Einstein’s help because Einstein’s reputation could attract the president’s attention.
Szilard prepared the draft and later dictated the English version after meeting Einstein on Long Island. Einstein signed the letter on August 2, 1939. It warned Roosevelt about the possibility of German atomic research and urged the United States to begin investigating uranium and nuclear weapons.
The letter did not itself create the Manhattan Project, but it helped prompt the U.S. government’s Advisory Committee on Uranium. Einstein signed the appeal but did not work on the Manhattan Project; security officials denied him clearance.