I grew up surrounded by a ring of Bomber Command 'dromes but too young to know of #3 but obviously I see now
not everyone had a lifetime of “Option 3ing” ahead of them
But there was a snag
#3 at 10% probably indicates mission but DCO was not necessarily 100%
competition because outside my local ring there were more 'fields staffed by folk who were "over paid, over sexed and".