Jack Currie in 'Lancaster Target', had the misfortune of having his service dress cap removed from the entrance hall of the sergeants mess. It had taken him nearly two years to crumple it into a comfortable ravaged condition ( turning a neutral colour in the process) , it fitted his head like a glove. He was most indignant.
A battered 'Ops cap' was most prized by operational crew, signifying long service, even if that wasn't the case.