The United States Navy has approximately 490 ships in both active service and the reserve fleet, with approximately 90 more in either the planning and ordering stages or under construction, according to the Naval Vessel Register and published reports. This list includes ships that are owned and leased by the U.S. Navy; ships that are formally commissioned, by way of ceremony, and non-commissioned. Ships denoted with the prefix "USS" are commissioned ships. Prior to commissioning, ships may be described as a "pre-commissioning unit" or PCU, but are officially referred to by name with no prefix. US Navy support ships are often non-commissioned ships organized and operated by Military Sealift Command. Among these support ships, those denoted "USNS" are owned by the US Navy. Those denoted by "MV" or "SS" are chartered.