The United States began the Cold War with a monopoly on nuclear arms. Although they were aware that the U.S.S.R. was trying to develop their own nuclear weapon, most American scientists estimated that the Soviets were well behind the U.S. in terms of developing an actual nuclear weapon. When the Soviets successfully deployed their first bomb in 1949, the new shocked the west. This set off an arms race where the U.S. began developing a more powerful hydrogen bomb, which they tested in 1952, confident that they now outpaced the Soviets own destructive capabilities significantly. The U.S. also began the secret Green Run project which they hoped would allow the U.S. Air force to detect any fallout from future Soviet nuclear tests.
The U.S. was again shocked when the U.S.S.R. exploded their own hydrogen bomb in 1953, although they didn’t copy the U.S. multistage design until 1955. Even more chilling was the successful development of the ICBM by the Soviets in 1957 which they showed off by launching Sputnik, the first man made space object. Once again, the threat of nuclear war was very real, and was not longer just relegated to potential raids by bombers.
The U.S. began building defenses, such as fallout shelters, large radar arrays and installing NIKE anti-ICBM missile systems across the U.S. These measures weren’t deemed secure enough, so the U.S. developed a strategy known as MAD (mutually assured destruction) in which both sides would refrain from attacking the other because the assurance of a second strike would be guaranteed.