SS United States is a retired ocean liner built between 1950 and 1951 for the United States Lines. She is the largest ocean liner constructed entirely in the United States and the fastest ocean liner to cross the Atlantic in either direction, retaining the Blue Riband for the highest average speed since her maiden voyage in 1952, a title she still holds. She was designed by American naval architect William Francis Gibbs and could be converted into a troopship if required by the Navy in time of war. United States maintained an uninterrupted schedule of transatlantic passenger service until 1969 and was never used for military applications.

An ocean liner is a type of passenger ship primarily used for transportation across seas or oceans. Ocean liners may also carry cargo or mail, and may sometimes be used for other purposes. Only one ocean liner remains in service today.