The U.S. Navy will redesignate 19 planned Virginia-class submarines with the Virginia Payload Module (VPM) as guided missile submarines (SSGNs). The change reflects their much larger missile capacity compared with standard Virginia-class attack submarines. Missile subs redesignated The U.S. Navy has announced a major shift in the way it classifies its next generation of Virginia-class submarines, redesignating 19 planned boats equipped with the VPM as guided missile submarines SSGNs instead of fast attack submarines (SSNs). It comes as the Navy prepares to retire its four Ohio-class guided missile submarines by the end of the decade. The final Ohio-class SSGN is expected to retire years before all 19 Virginia SSGNs are delivered, creating a temporary reduction in undersea missile capacity.