high altitude training
"One thing which I found very interesting was the amount of high-level flying up in 40s which went on back in RAFG in the 1950s."
Beags, we were doing it in the 60s too: as a JP QFI in the 60s I remember syllabus High Level sorties involving climb to 35,000 ft for GH - in the unpressurised JP4.
On my DF/GA Hunter course at Chiv in 1970 we were still practising High Level Battle at 40 grand/0.9 Mach. Made your eyes water if you tried to use flap to cut the corrners!