Revealing mistake: Technical Glitch: In the opening scene before the opening credits. The British are being run out of one of the last remaining fields in France. The Sergeant is burning the "lame ducks" when German planes attack. A German plane attacks almost directly toward the camera, you hear machine gun noises but no effects. Next a plane attacks from right to left, you hear machine gun noises and see the effects indicating the bullets striking the target. After the second plane has gone you see the effects of the first planes attack.
Revealing mistake: In the opening scene when the Hurricanes take off from the makeshift airstrip in France, well established earth-banked aircraft pens can be seen in the background. This indicates that the Hurricanes took off from a well established military airfield.