The list of hull classifications comprises an alphabetical list of the hull classification symbols used by the United States Navy to identify the type of a ship. The combination of symbol and hull number identify a modern Navy ship uniquely. A heavily modified or repurposed ship may receive a new symbol, and either retain the hull number or receive a new one. Also, the system of symbols has changed a number of times since it was introduced in 1907, so ships' symbols sometimes change without anything being done to the physical ship.