All current and planned U.S. Navy submarines are nuclear-powered, as only nuclear propulsion allows for the combination of stealth and long duration, high-speed sustained underwater movement that makes modern nuclear submarines quite vital to a modern blue-water navy. The U.S. Navy operates three types: ballistic missile submarines, guided missile submarines, and attack submarines. U.S. Navy (nuclear) ballistic missile submarines carry the stealthiest leg of the U.S. strategic triad (the other legs are the land-based U.S. strategic missile force and the air-based U.S. strategic bomber force). These submarines have only one mission: to carry and, if called upon, to launch the Trident nuclear missile. The primary missions of attack and guided missile submarines in the U.S. Navy are peacetime engagement, surveillance and intelligence, special operations, precision strikes, and control of the seas. To these, attack submarines also add the battlegroup operations mission. Attack and guided missile submarines have several tactical missions, including sinking ships and other subs, launching cruise missiles, gathering intelligence, and assisting in special operations.
As with other classes of naval vessels, most U.S. submarines (or "boats") are named according to specific conventions. The boats of the current U.S. ballistic missile submarine class, Ohio class, are named after U.S. states. As the four current U.S. guided missile submarines are converted Ohio-class boats, they have retained their U.S. state names. The members of the oldest currently-commissioned attack submarine class, the Los Angeles class, are typically named for cities. The follow-on Seawolf class' three submarines—Seawolf, Connecticut and Jimmy Carter—share no consistent naming scheme. With the current Virginia-class attack submarines, the U.S. Navy has extended the Ohio class' state-based naming scheme to these submarines. Attack submarines prior to the Los Angeles class were named for denizens of the deep, while pre-Ohio-class ballistic missile submarines were named for famous Americans and foreigners with notable connections to the United States.