The most important development in terms of delivery in the 1950s was the introduction of intercontinental ballistic missiles (ICBMs).
Missiles had long been regarded the ideal platform for nuclear weapons, and were potentially a more effective delivery system than strategic bombers, which was the primary delivery method at the beginning of the Cold War.
In the 1950s both the United States and Soviet Union had enough nuclear power to obliterate the other side. Both sides developed a capability to launch a devastating attack even after sustaining a full assault from the other side, called a second strike. Both sides were unaware of the capacity of the enemy's arsenal of nuclear weapons. The Americans suffered from a lack of confidence, and in the 1950s they believed in a non-existing bomber gap.
An additional controversy formed in the United States during the early 1960s concerned whether or not it was certain if their weapons would work if the need should occur. All of the individual components of nuclear missiles had been tested separately, but it had been infeasible to test them all combined.