The IX (unclassified–miscellaneous) hull classification symbol is used for ships of the United States Navy that do not fit into one of the standard categories. While many of the vessels in this category were former yachts, it also includes retired warships, vessels used in mobile bases by service squadrons (command ships, barracks ships, bulk storage ships, unnamed barges, and floating shipyard equipment), training equipment and simulators (including two Great Lakes-based paddlewheel aircraft carriers), war prizes, experimental vessels, and armed decoys (Q-ships).