Handlebar Moustaches in RAF

Basil Stapleton told me it was to try and look older

I was led to believe that QR’s for the RAF forbade growing a moustache below the top lip. Sideburns and full beards were also ruled out.

And I remember being told by someone who was in the RFC that it was an attempt to disguise lip injuries in the days seat harness was a simple strap at waist height and like Topsy the idea just grew (and spread!).

My suggestion – which is not based on any in depth research…

I suspect many RFC/RAF traditions originate from the Army officers who transferred to a flying career. I understand many of these pioneers were ex-cavalry. Cavalrymen also wore moustaches and the principal division of a Cavalry regiment was a squadron.
M-62A

I’ve read several times that some airmen were so young looking, they grew moustaches, not necessarily handlebars, to look older than their years. David Shannon of 617 Squadron is an example. Gibson can be seen with one in some pre-617 photos. But they were in many cases indeed very young. I guess the handlebar became an extension of that, literally.