A ship class is a group of ships of a similar design. This is distinct from a ship type, which might reflect a similarity of tonnage or intended use. For example, USS Carl Vinson is a nuclear aircraft carrier (ship type) of the Nimitz class (ship class). Ships in a class often have names linked by a common factor: e.g. Trafalgar-class submarines' names all begin with T (Turbulent, Tireless, Torbay); and Ticonderoga-class cruisers are named after American battles (Yorktown, Bunker Hill, Gettysburg, Anzio). Ships of the same class may be referred to as sister ships.