SSBN is the United States Navy Hull classification symbol for a fleet ballistic nuclear missile submarine. The SS denotes a submarine, the B denotes ballistic missile capability, and the N denotes nuclear power. It differs from SSN, the fast attack submarine in that the primary mission of the SSBN is nuclear deterrence while the SSN is primarily a hunter/killer.
The SSBN also is unique in that it has 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 strategic nuclear submarines are labeled "SNLE", for Sous-marin Nucléaire Lanceur d'Engin ("Device-Launching Nuclear Submarine"); their crews are blue and red crew.
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