SSN (hull classification symbol)

SSN is the US Navy hull classification symbol for nuclear-powered general-purpose attack submarines. SS means "Submarine, General" according to the NATO Standard Ship Designator System (STANAG 1166,) with SSN referring to a "Submarine, Attack, Nuclear" vessel. The "SS" designator is consistent with other examples of STANAG 1166 using double letter referring to a type of vessel – for example, "BB" designates a Battleships, "DD" is a Destroyer, "CC" a Cruiser, "FF" a Frigate, and so on.