SSBNs

A ballistic missile submarine is a submarine capable of deploying submarine-launched ballistic missiles (SLBMs) with nuclear warheads. These submarines became a major weapon system in the Cold War because of their nuclear deterrence capability. They can fire missiles thousands of kilometers from their targets, and acoustic quieting makes them difficult to detect, thus making them a survivable deterrent in the event of a first strike and a key element of the mutual assured destruction policy of nuclear deterrence. Many ballistic missile submarine policies also include provisions for nuclear first strike as well. For these reasons, 70% of nuclear warheads in the United States are carried by ballistic missile submarines.