Submarine-launched ballistic missile

A submarine-launched ballistic missile (SLBM) is a ballistic missile capable of being launched from submarines. SLBMs almost exclusively carry nuclear weapon warheads, and play an important role in nuclear strategy as a highly reliable and non-vulnerable second strike option.

Modern variants 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 an inertial navigation system in combination with a celestial navigation system. Submarine-launched ballistic missiles operate in a different way from submarine-launched cruise missiles.

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. 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.

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 a multiple re-entry vehicle, 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.

Modern submarine-launched ballistic missiles are closely related to intercontinental ballistic missiles (ICBMs), with ranges of over 5,500 kilometres (3,000 nmi), and in many cases SLBMs and ICBMs may be part of the same family of weapons.