Submarine-launched ballistic missile

A submarine-launched ballistic missile (SLBM) is a ballistic missile capable of being launched from submarines. SLBMs almost exclusively carry one or multiple nuclear warheads, and play an important role in nuclear strategy as a highly reliable and non-vulnerable second strike option. Nuclear-armed SLBMs are operated by China (JL-3), France (M51), India (Sagarika), Russia (Sineva, Lajner, and Bulava), the United Kingdom and the United States (both Trident II). South Korea is the only nation developing a conventionally-armed SLBM, the Hyunmoo 4-4.

SLBMs typically have similar ranges and designs to intercontinental ballistic missiles (ICBMs), which range over 5,500 kilometres (3,000 nmi). Modern variants favor solid propellant and usually deliver multiple independently targetable reentry vehicles (MIRVs), each of which carries a strategic nuclear warhead and allows a single launched missile to strike several targets. SLBMs typically use a combination of inertial and celestial navigation systems. Some SLBMs have also been used in a tactical nuclear weapon role, such as the United States W76 Mod 2 warhead mated to the UGM-133 Trident II missile.

The Soviet Union tested the world's first SLBM, the R-11FM, in 1955, and became the first country to operate ballistic missile submarines with the R-11FM in 1956. The United States Navy first developed the UGM-27 Polaris, operational from 1961. The Polaris A-3 was the first missile to use multiple re-entry vehicles, a nuclear cluster munition. The US Navy remains the largest operators of SLBMs, with 280 Trident II missiles, followed by the Russian Navy with 192 total SLBMs.