A ballistic missile submarine is a submarine equipped to launch ballistic missiles (SLBMs), such as the Russian R-29 or the American/British Trident.
Although some early models had to surface to launch their missiles, modern vessels typically launch while submerged at keel depths usually less than 50 meters (164 feet). Ballistic missile submarines differ from attack submarines and cruise missile submarines; while attack submarines specialise in combat with other naval vessels (including enemy submarines and merchant shipping), and cruise missile submarines are designed to attack large warships and tactical targets on land, the primary mission of the ballistic missile is nuclear deterrence. Accordingly, the mission profile of a ballistic missile submarine concentrates on remaining undetected, rather than aggressively pursuing other vessels.
Ballistic missile submarines are designed for stealth, to avoid detection at all costs. They use many sound-reducing design features, such as anechoic tiles on their hull surfaces, carefully designed propulsion systems, and machinery mounted on vibration damping mounts.
The need to accommodate SLBMs means that ballistic missile submarines are larger than all other classes of submarine. The most obvious examples of this were the later Russian Navy Delta III and IV classes, as well as the Typhoon-class and the American Ohio-class.
SSBN is the United States Navy's hull classification symbol for a nuclear-powered, ballistic nuclear missile-carrying submarine. In US naval slang, ballistic missile submarines are called "boomers", while in Britain, they are referred to as "bombers".
SSBN is a designation for Ballistic Missile Submarines (Nuclear Powered), as set forth in [SECNAVINST 5030.8] .
The French Navy strategic nuclear submarines are designated "SNLE", for Sous-marin Nucléaire Lanceur d'Engins ("Device-Launching Nuclear Submarine").
Many navies use two crews per boat to maximize patrol time. In the U.S. Navy, the two crews are called blue crew and gold crew. In the Royal Navy, the two crews are called port crew and starboard crew. The French Navy uses blue and red for its crews.
Ballistic missile submarines equipped with nuclear warheads also serve as the third leg of the nuclear triad. The invisibility and mobility of submarines not only gives the provided nation with a reliable means of deterrence against an attack but also a surprise first strike capability.
Ballistic missile submarines are specially designed to carry and launch intercontinental nuclear-tipped missiles from vertical launching tubes. An American Ohio class ballistic missile submarine is 170.7 m (560 ft) long—much longer than an attack sub—and carries a crew of 163. These submarines form part of a country’s strategic nuclear force. Military strategists use the threat of a retaliatory submarine-launched missile attack to deter an enemy from starting a nuclear war.
The strategy is simple: Even if the aggressor were able to destroy all of its enemy’s land-based missiles in a first-strike, the enemy’s ballistic missile submarines could deliver a devastating counter-blow, thus assuring what defense planners have called mutual assured destruction. Because of their mission to deter attack on their respective countries, ballistic missile submarines are designed to operate with extreme quiet in deep ocean patrol and evade detection during their patrols, which last from a few weeks to as many as 70 days at sea. Since an enemy cannot detect these subs, they pose a constant threat to a potential aggressor.
The U.S. Navy also operates several smaller submarine-type underwater vessels. These are much smaller than submarines, and are used for military research, underwater rescue, and salvage operations. For information on these and other underwater vehicles, see Submersible Craft.