Acruise missile submarine is asubmarine that carries and launchescruise missiles (SLCMs consisting ofland-attack cruise missiles andanti-ship missiles) as its primary armament. Missiles greatly enhance awarship's ability to attack surface combatants and strike land targets; althoughtorpedoes are a more discreet option for submerged submarines, missiles give a much longerstand-off range, shorter time to impact the target, as well as the ability to engage multiple targets on different headings at the same time. Many cruise missile submarines retain the capability to deploynuclear warheads on their missiles, but they are considered distinct fromballistic missile submarines due to the substantial differences between the two weapons systems' flight characteristics; cruise missiles fly aerodynamically using flight surfaces like wings or fins, while aballistic missile uses its engine power alone as it mayexit the atmosphere.

TheUnited States Navy'shull classification symbols for cruise missile submarines areSSG andSSGN – theSS denotes submarine, theG denotesguided missile, and theN denotes that the submarine isnuclear-powered.

The earliest designs of cruise missile submarines had to surface to launch their missiles, while later designs could do so underwater via dedicatedvertical launching system (VLS) tubes. Many modernattack 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 an overlap between cruise missile submarines and traditional attack submarines. Nonetheless, vessels classified as attack submarines are designed to use torpedoes as their main armament and have a more multi-role mission profile due to their greater speed and maneuverability. This is in contrast to cruise missile submarines which are typically larger, slower boats carrying a larger number of missiles and often possess a specialcompartment dedicated solely to the cruise missile tubes.

The U.S. Navy'sfirst cruise missile submarines were developed in the early 1950s to carry theSSM-N-8 Regulus missile. The first of these was a converted World War II eraGato-classsubmarine,USS Tunny, which was fitted with a hangar capable of carrying a pair of Regulus missiles.Tunny was used as a test-bed for developing techniques of use for the missile system, before a second boat,USS Barbero was subsequently converted. Starting in 1957, these two boats undertook the firstnuclear deterrent patrols.^[1]

Subsequently, two larger diesel submarines of theGrayback-class were purpose built for the carriage of the Regulus missile, with each capable of accommodating up to four missiles, while a further boat, the nuclear-poweredUSS Halibut, could carry up to five missiles. Between September 1959 and July 1964, the five Regulus missile boats undertook deterrent patrols in the Pacific Ocean,^[2] in concert with the newly commissionedGeorge Washington-class ballistic missile submarines (SSBN) in the Atlantic, until sufficient SSBNs were in service to replace them.

From 2002 to 2008, the U.S. Navy modified the four oldestOhio-class submarines:Ohio,Michigan,Florida, andGeorgia into SSGNs. The conversion was achieved by installing VLS in amultiple all-up-round canister (MAC) configuration in 22 of the 24 missile tubes, replacing oneTrident missile with seven smallerTomahawk cruise missiles. The two remaining tubes were converted tolockout chambers for use by special forces personnel. This gave each converted submarine the capability to carry up to 154 Tomahawks. The large diameter tubes can also be modified to carry and launch other payloads, such asUAVs orUUVs although these capabilities have not yet been fully implemented. In addition to generating a significant increase in stand-off strike capabilities, this conversion also counts as an arms reduction towards theSTART II treaty,^[3][4] because it reduces the number of nuclear weapons that are forward-deployed. USSFlorida (SSGN-728) launched cruise missiles againstLibyan targets as part ofOperation Odyssey Dawn in March 2011.

Currently,Virginia-class submarines (Block I–IV) serve as universal ships, bothattack submarines and cruise-missile submarines with 12 ×Vertical launching system (VLS) forTomahawk cruise missiles. The futureVirginia-class (Block V) submarines with 40Tomahawk cruise missiles are slated to supplement and eventually replace the Ohio SSGNs when they are retired; theUSS Ohio itself is more than 40 years old.^[5]

• US Navy SSGNs
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  USS Cusk fires aJB-2 Loon missile, 1951
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  USS Tunny fires aRegulus I, 1956
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  Tomahawk test-fire fromUSS Florida, 2008
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  USS Georgia underway, 2012

TheSoviet Navy (and its successor, theRussian Navy) has operated a wide variety of dedicated cruise missile submarines (unbolded project numbers were prototypes/never entered military service):

Khruschev encouraged the development of missiles in the Soviet Union; thus the issues ofeffective nuclear deterrence and delivery andUS Carrier Strike Groups were to be solved through advances in missilery. Submerged submarines are more concealable than surface ships; missiles carried upon them were therefore safer from attack by NATO surface fleets, land-based aircraft, and long-rangepatrol bombers. Thus the strategic and tactical strike missions were solved through the equipment of submarines with large, long-range cruise missiles: first through themodification of existing boats, then by boats being built for the task.

The Whiskey variants and Echo I cruise missile submarines deployed with a nuclear land attack version of theP-5 Pyatyorka (SS-N-3 Shaddock) from the late 1950s to 1964, concurrently with the US Regulus force, until the strategic land attack mission was transferred entirely to the SSBN force. Along with the Julietts and Echo IIs, these continued as SSGs or SSGNs with an antiship variant of the P-5 until circa 1990. TheEcho Is were an exception; they could not accommodate the anti-ship targeting radar and served as SSNs after the land attack missiles were withdrawn.^[10]

Apart from true guided-missile submarines, late-Soviet attack submarines could launch various types oftorpedo tube-launched missiles starting with theRK-55 and continuing with theKalibr family of missiles. Cruise-missile capable Soviet submarines may have a different designation to incapable sister boats (Victor III (Project 671RTM) boats became Project 671RTMK as they gained this ability, K for Крылатая ракета; cruise missile).^[11] Due to standardization of torpedo tube diameters, which are533 mm,modern Russian attack submarine classes (even thedieselKilo andLada) are capable of launching long-range strategic cruise missiles from their torpedo tubes, without needing specialized compartments for missile tubes.^[12][13]

• Soviet and Russian ДПЛРК and ПЛАРК (Diesel-/Atomic Cruise-missile Submarines)
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  K-222, the sole Project 661 submarine underway, 1983
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  A Project 651 boat underway, 1986
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  K-24 (nowU-461 of thePeenemünde Maritime Museum), Project 651Juliett cruise missile submarine, with rear SS-N-3 Shaddock launch tubes in raised position
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  INS Chakra underway, c. 1988
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  Project 949 (Oscar-I) underway. The Oscar-classes are notably girthy; the very large P-700 missiles were placed outside thepressure hull, twelve launch tubes on each side
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  Project 949A (Oscar-II) underway. Pr. 949A boats had a different tail fin which accommodated thetowed-array sonar (cylinder visible at the bottom of photo), an easy way to distinguish this class from its immediate predecessor

• List of submarine classes in service
• List of submarine operators
• List of NATO reporting names for guided-missile submarines
• Missile boat (surface ship)
• Transporter erector launcher (land vehicle)

• Gardiner, Robert; Chumbley, Stephen (1995).Conway's All the World's Fighting Ships 1947–1995. London: Conway Maritime Press.ISBN 1-55750-132-7.
• US Stingray style sub motherships test missiles.The Register, 31 May 2007