On the subject of medical categories:
When I joined the RAF in 1959 I failed the colour vision test and thus could not become an Apprentice Ground Wireless Fitter at Halton. However, I could train as a Boy Entrant Telegraphist at Cosford. I duly passed out in 1961 and after tours at Driffield, Sharjah, MOD AIR, Akrotiri and 38 Group (Tangmere) I found myself posted to 604 Forward Air Control Unit which was part of 24 (Air Portable) Brigade at Crownhill Fort, Plymouth. I could not drive so was eventually sent off to RAF St Athan's driving school. It was only when I got my F1629 that I noticed that despite my medical records showing "Colour blind" it said "Colour perception - safe". As I was not going to be driving on many airfields I decided to keep quiet about it!
Incidentally, I was taken seriously ill whilst at 604 FAC (recurrence of childhood asthma) and was treated by the Royal Navy at HMS Drake. The result of this was that, as far as i know, I was the only member of the RAF who was officially "P7 - unfit for seagoing duty".