HMS CUMBERLAND was used as a trials cruiser after conversion for this role at Devonport completing in May 1951. For the next eight years this ship was used as a trials platform for many different types of weapons systems as well as of smaller pieces of equipment prior to their introduction into Fleet use. She was broken up 1959.
The Americans were making their own V1s (had a silly name) with minor mods as early as 1945 and carried out the first submarine launch in 1946 - so I suspect it was an early conceptual 'Cruise missile" or "Exocet" shot down by an early version. of "Phalanx"
HMS Cumberland has a veterans' association - could try them for more info.