Surprisingly in late 1939 and early 1940 thousands of trainee RAF pilots (many with extensive flying hours) were transfered to other trades due to a lack of training aircraft.
Many were far more experienced than the RAF's own replacements, some of which arrived on squadrons with only 10 hours basic flying experience and without having completed any OTU courses.
This was due to a reduction in OTU courses from 6 months to only 4 weeks, leaving the squdarons to apply the final training with pilots who had not yet mastered their powerful fighters and who had received little training in blind or night flying, navigation or gunnery.