USS stands for "United States Ship" and is a ship prefix used to identify a commissioned ship of the United States Navy. The prefix is used in official documents to identify a commissioned ship of the Navy, and applies to a ship only while it is in commission. Before commissioning, or after decommissioning, a ship is referred to by name, with no prefix. Civilian-manned ships of the Military Sealift Command (MSC) are not commissioned ships, and their status is "in service," rather than "in commission." They are, nonetheless, Navy ships in active national service, and the prefix "USNS" (United States Naval Ship) was adopted to identify them.