Jewish culture and many Jewish scientists had a significant role in the project. The theoretical physicist Robert Oppenheimer, often considered as the ""father of the atomic bomb"", was chosen to direct the Manhattan Project at Los Alamos National Laboratory in 1942. The physicist Leó Szilárd, that conceived the nuclear chain reaction; Edward Teller, ""the father of the hydrogen bomb"" and Stanislaw Ulam; Eugene Wigner contributed to theory of Atomic nucleus and Elementary particle; Hans Bethe whose work included Stellar nucleosynthesis and was head of the Theoretical Division at the secret Los Alamos laboratory; Richard Feynman, Niels Bohr, Victor Weisskopf and Joseph Rotblat.
Soviet atomic bomb project and British scientists, Russian physicist Georgy Flyorov suspected that the Allied powers had secretly been developing a "superweapon" since 1939. Flyorov wrote a letter to Stalin urging him to start this program in 1942. Initial efforts were slowed due to the German invasion of the Soviet Union and remained largely composed of the intelligence knowledge gained from the Soviet spy rings working in the U.S. Manhattan Project. After Stalin learned of the atomic bombings of Hiroshima and Nagasaki that ended the Pacific War in 1945, the program was pursued aggressively and accelerated through effective intelligence gathering about the German nuclear