A ballistic missile submarine is a submarine 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 very difficult to detect (see acoustic signature), 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. Their deployment has been dominated by the United States and the Soviet Union / Russia, with smaller numbers in service with France, the United Kingdom, China, and most recently India.