Rumour at Cranners during flight cadet days was that the 5A mess kit (stiff-fronted shirt, detachable winged collar, white waistcoat, black bow tie) was required because females were only allowed over the threshold twice a year for grad balls, and once you had your 5A on it functioned better than the average chastity belt. (It was always useful the following day to keep your eyes peeled to locate and restock collar and shirt studs that had popped-off during the evening.)
ISTR that one of the main reasons for the demise of the outfit was the increasing difficulty in finding laundries that could actually wash and starch the shirt and collar.