SSGN

A cruise missile submarine is a submarine that launches cruise missiles (SLCMs) as its primary armament. Cruise missile and dedicated anti-ship missiles greatly enhance a vessel's ability to attack surface combatants. Torpedoes are a more stealthy option, but missiles give a much longer stand-off range, as well as the ability to engage multiple targets on different headings at the same time. Many cruise missile submarines retain the capability to deploy nuclear warheads on their missiles, but they are considered distinct from ballistic missile submarines due to the substantial differences between the two weapon systems characteristics.

Originally early designs of cruise missile submarines had to surface to launch their missiles, while later designs could do so underwater via dedicated vertical launching system (VLS) tubes. Many modern attack submarines can launch cruise missiles (and dedicated anti-ship missiles) from their torpedo tubes while some designs also incorporate a small number of VLS canisters, giving some significant overlap between cruise missile submarines and traditional attack submarines. Nonetheless, vessels classified as attack submarines still use torpedoes as their main armament and have a more multi-role mission profile due to their greater speed and maneuverability, in contrast to cruise missile submarines which are typically larger slower boats focused on the long distance surface strike role.

The United States Navy's hull classification symbols for cruise missile submarines are SSG and SSGN - the SS denotes submarine, the G denotes guided missile, and the N denotes that the submarine is nuclear-powered.

The U.S. Navy's first nuclear deterrent patrol submarines were five submarines equipped with the Regulus missile: USS Tunny (SSG-282), USS Barbero (SSG-317), USS Grayback (SSG-574), USS Growler (SSG-577) and USS Halibut (SSGN-587). Tunny and Barbero were modified World War II Gato-class submarines, while Grayback, Growler, and Halibut were custom-made launch platforms. These ships were redesignated with the removal of the Regulus missile from service in 1964.

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Wikipedia