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.
Mark 18 nuclear bomb placed in the fissile pit to reduce the risk of accidental high yield detonation, and removed during the last steps of the arming sequence. Beginning in March 1953, the United States deployed a number of Mark 18 bombs. A total of 90 were manufactured and placed in service. The weapon had a short lifetime, and was replaced by thermonuclear weapons in the mid-1950s. The Mark 18 weapons were all modified into lower yield Mark 6 nuclear bomb variants in 1956. Mark 18 nuclear bomb The Mark 18 nuclear bomb, also known as the SOB or Super Oralloy Bomb, was an