United States Ship (abbreviated as USS or U.S.S.) is a ship prefix used to identify a commissioned ship of the United States Navy and applies to a ship only while she is in commission. Before commissioning, she is referred to as "Pre-commissioning Unit" (PCU). After decommissioning, she is referred to by name, with no prefix. Non-commissioned Navy ships go by the prefix USNS, which stands for United States Naval Ship.