Why did the Royal Navy not adopt CM, DM, and FM for missile ships, and which system might a continuing British Empire use?
Short answerNATO identification and the established pennant-number system already classified ships well enough, and the letter M carried other associations such as minelayers.
NotesA continuing British Empire is expected to retain the Royal Navy's own identification system. NATO classification is explained through its practical value to multinational commanders: a designation helps identify an arriving ally's ship type without looking up that individual vessel. The proposed letter M also creates ambiguity because CM and DM already suggest cruiser minelayers and destroyer minelayers. The Royal Navy's established use of pennant numbers provides the other part of the explanation.