The ballistic missile submarine USS Pennsylvania (SSBN 735) arrives at her new homeport at the Naval Submarine Base, Bangor, Wash., following a voyage from her previous base at Kings Bay, Ga. Strategic deterrence has been the sole mission of the fleet ballistic missile submarine (SSBN) since its inception in 1960. The SSBN provides the nation's most survivable and enduring nuclear strike capability. The Ohio-class submarine, of which Pennsylvania is one, replaced aging SSBNs built in the 1960s and is far more capable. U.S. Navy photo by Brian Nokell.