When they were makong the film the problem came up of actors on an RAF station wandering around in uniform and airmen not knowing of they were 'real officers' or not. I believe Richard Todd the actor playong Guy Gibson came up with the actors would wear brown shoes to identify them. Being a black and white film there was no obvious difference. Richard Todd had a distingushed war career in which he was part of the parachute drop to support the taking of Pegasus brodge.
just to add two pieces of organ music from Liverpool Cathedral.