Modern nuclear submarines are divided into attack and ballistic missile submarines.
Attack submarines are those that are designed to sink enemy submarines and surface ships, the most famous of which are the USS Los Angeles and the Seawolf classes of submarines. Both have radar-guided missiles and the self-targeting Tomahawk cruise missiles, which can hit any land- or sea-based target of up to 2,000 kilometres away.
Ballistic missiles submarines form the core of the world's nuclear powers' second-strike ca pacity.
The most formidable class of missile submarine is the 27,000- tonne Russian Typhoon, which is almost twice as long as a football pitch. It is equipped with 20 SS-N-20 ballistic missiles, each of which can carry nine nuclear warheads.
Currently only the United States, Britain, France, Russia and China have nuclear submarines.