Why Royal Navy type numbers skip unbuilt designs

Which ship types did the Royal Navy not adopt because existing ships already did the job?

Potentially hundreds of paper designs; skipped type numbers record options rejected as requirements and existing capabilities evolved.

There is no short definitive list because major navies continuously examine designs that never become orders. Type 43 and 44 destroyers and Type 24 and 25 frigates illustrate how numbered concepts can be bypassed as requirements change. Their skipped numbers preserve traces of options in an ongoing design process rather than a neat list of ships cancelled for one reason. Even a foreign-derived design such as Type 31 is heavily adapted, reflecting the Royal Navy's preference to reshape a concept around British needs rather than simply buy an unchanged foreign warship.