The abbreviation USS on a ship stands for United States ship. This prefix is used to identify a commissioned ship of the U.S. Navy. Other countries' ships are identified by different prefixes.
If the ship has not yet been commissioned, it is known as a Pre-commissioning Unit, or PCU. Once decommissioned, the ship is only referred to by its name without a prefix. The abbreviation USS was present as early as 1790 but was not exclusively used. President Theodore Roosevelt issued an order in 1907 establishing that all vessels of war and vessels of the U.S. Navy feature the USS prefix before the name of the vessel.