Type system of the Royal Navy

The Type system is a classification system used by the British Royal Navy to classify surface escorts by function. The system evolved in the early 1950s, when the Royal Navy was experimenting with building single-purpose escort vessels with specific roles in light of experience gained in World War II. The original (July 1950) numbering scheme was:
Type 1X were Anti-Submarine (ASW) Frigates (when the numbers ran out in the 1960s, ASW Frigates continued as the Type 2X series).
Type 4X were Anti-Aircraft (AAW) Frigates (this later evolved into the "Destroyer" Type series).
Type 6X were Aircraft-Direction (ADW) Frigates.
Type 8X were Multi-Role ships. An Admiralty Fleet Order defined these ships as "Destroyers" if they could achieve "fleet speed" or as "Sloops" if they could not.
The following Type numbers are known to have been used, or proposed;