From WW1 -
One of my favourite books is 'Flight Path' by Frank T Courtney...he was not allowed to join the RFC as a pilot because he wore glasses and also was an experienced a/c mechanic !! rare in those days !!
He was posted as an Air Mechanic 2nd class (AM2) to Farnborough and because he had a pilots ticket he managed to become an unofficial instructor,eventually given his wings (still as an AM2) without a military flying course - he even managed to get into action against Trenchards wishes (because of his spectacles)...great book,he later became a freelance test pilot inc for Cierva on autogiros.