What really pushed the Cold War to a true Armageddon Apocalypse Judgement Day situation is the appearance of ICBM carrying submarines. The public were sold the idea that this weapon system is going to be used as some sort of counter strike once a nuclear strike happens. The problem with that is that this combination of nuclear tipped missiles and the stealth of submarines makes it the perfect candidate for a first strike scenario.
The first generation nuclear missiles that were used on a submarine goes by the name of Polaris. The first submarine to launch a Polaris out of its belly is the USS George Washington. They tested the weapon on July 20, 1960 somewhere in the Pacific.
Today’s missile submarines carry around 24 ballistic missiles, each missile has eight nuclear warheads which can be guided independently to a target. By the way, each nuclear warhead yields up to 475 kilotons of TNT (24 times Hiroshima).