Ship Naming Prefixes
The prefix "USS," meaning "United States Ship," is used in official documents to identify a commissioned ship of the Navy. It applies to a ship while she is in commission. Before commissioning, or after decommissioning, she is referred to by name, with no prefix. Civilian-manned ships of the Military Sealift Command (MSC) are not commissioned ships; their status is "in service," rather than "in commission." Nevertheless, they are Navy ships in active national service, and the prefix "USNS" (United States Naval Ship) was adopted to identify them. Other Navy vessels classified as "in service" are simply identified by their name (if any) and hull number, with no prefix.
In the early 1800’s, there was no fixed form for Navy ship prefixes. Ships were rather haphazardly identified, in correspondence or documents, by their naval type, such as “U.S. Frigate ____,” by their rig, such as “United States Barque ____,” by their function such as “United States Flag-Ship ____,” or they might just identify themselves as "the Frigate _____," or as "Ship ______." In the 1790’s, the term "United States Ship" (USS) began to be used and by the late 1800’s it was in frequent use.