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 6X were Aircraft-Direction (ADW) frigates.
An Admiralty Fleet Order defined these ships as "destroyers" if they could achieve "fleet speed" or as "sloops" if they could not.