Beagle .... Thanks for the link to Operation Hallmark. Blimey the things that were happening in those days and all of us young lads thought it was all about beer and Bratwurst.
Given that the Pembrokes used to be met, on occasion, by an RVT truck ... I believe that the letters stood for Radio Vehicle Transport ... we always thought that it may have been secret squirrel stuff/black boxes etc. that was being removed.