When the USSR tested it's nuclear technology, therefore acquired nuclear weapons capability, a nuclear arms race and begun.
In March 1954, the USA successfully tested a lithium H-bomb (1500 times more powerful than the bomb used at Hiroshima in 1945).
(The Strategic Air Command (1948) was the USA's defence system against nuclear threat, and became an all-jet force focused on any strategic bombers).
By September the USSR had similar technology, and by 1955 they tested an airborne H bomb, 100 times more powerful than their first attempts.