The U.S. Navy maintains the Naval Vessel Register, which is the official list of U.S. Naval ships and service craft. On the NVR website at NVR.Navy.mil, the ships are listed and can be searched by hull classification symbol or unit identification code.
The U.S. Navy classifies ships and service craft by combining the hull classification symbol, which identifies what type of craft the vessel is, with a hull number to identify each craft uniquely. On the NVR, ships are listed by hull type or by unit identification number. The NVR can only be accessed from an Internet connection that originates in the United States, as it is hosted on a Department of Defense computer.