Tomjoad,
Thanks for that, I think! I believe that I was trying to suggest that the reason that the aircraft technical trades had the anomalous J/T and C/T relates to the need for extra levels of training and experience for those trades. I was certainly not complaining about the Vulcan course, it kept me on my toes. I do suspect that to some degree all RAF trades had precedence in the RN and Army, and therefore their rank structures may have dictated the set up I was involved with. Hopefully someone better qualified than me could explain where these ranks came from, why they were maintained and why the modern service has decided to ditch them. For me, at 60, it has little consequence, just historical interest.
Smudge
PS. 4maststacker, exactly what I wondered. If other trades were subject to such exigencies, then was there a need for the "extra" ranks.