In the opening scene, It shows multiple Lancaster bombers flying in formation at night, in reality this was impossible as they flew with no navigation lights so not to be seen. Each aircraft on a raid flew the same flight path just at slightly different times so to arrive at the target usually within twenty minutes of each other.
The RAF uniforms in the film are navy blue. This is incorrect as RAF uniforms from 1918 to present were a medium blue. Very obvious mistake.
Douglas, the Flight Lieutenant, constantly salutes while not wearing a hat. This is not done in the RAF.
Commissioned Officers do not enter the Sergeants Mess except for formal functions.
All the shirts in the RAF in World War 2, and in fact up until 1971 were 'Collar unattached' which means the collars were attached by front and back collar studs. It meant that having the top button and the tie down could never have happened as shown when they are relaxing.
Kate refers to Flight Lieutenant Miller as Lieutenant Miller. She would never abbreviate it like that.
A modern radiator is visible in Douglas Miller's family home. Attempts to cover one failed as the thermostatic control can be seen.
In addition to the saluting errors noted elsewhere, officers do not salute sergeants, as Flight Lieutenant Miller does when approaching his Lancaster for the first time.
No RAF sergeant would call a WAAF officer "Kate" or "my dear" on duty.