Around 1966/7 there was a trial with an aircrew No 2 that had zips in the jacket instead of flap pockets.
Wasn't that a Bomber Command thing?
Beagle or P-N will know. I remember a PO who was a chopped pilot turning up at Catterick to do the Regiment officers' course in one on those things, complete with Regiment flashes. I think it lasted till lunchtime when he was ordered back to the mess to change. Mind you he didn't last any longer as a potential rockape than he had as a pilot!