United States Ship is a ship prefix used to identify a commissioned ship of the United States Navy and applies to a ship only while it is in commission. Before commissioning, the vessel may be referred to as a "pre-commissioning unit" (PCU), but is officially referred to by name with no prefix. After decommissioning, it is referred to by name with no prefix, though people commonly refer to those ships with the prefix "ex-", as in ex-ship name. In-service but non-commissioned Navy ships go by the prefix USNS, which stands for United States Naval Ship.