In the sequence when Mathilde exits the car and silently waves goodbye to Gerbier, in response he rolls his window up completely, yet in the very next shot his window remains open as the car drives away.
When the prisoners share cigarettes among one another, one of the men saves his cigarette for later and puts it behind his right ear. In the next shot of him, the cigarette isn't there, but he picks it from behind his ear a few seconds later.
The submarine used in the film is a French Navy's Aréthuse-class submarine, Argonaute (S636) (even the number and name visible during boarding scene). It was launched on 23 October 1958 which is more than 15 years after the events that take place in the film.
In the end, it says "dimanche 23 février 1943" (Sunday, 23rd February, 1943) although it was a Tuesday.
When Gerbier is being taken to the concentration camp at the beginning of the film and the guard driving the police van makes an unexpected stop at the house, it is clear that the rain is only falling in front of the camera and directly on the van. Only a few feet away, no raindrops are hitting the mud or the puddles of water.
The shot of the British Whitley bomber under fire from German flak just doesn't work. An unloaded Whitley, especially one on a covert mission behind enemy lines where speed is essential, could manage about 250 miles an hour. This means that during the 1.5-second shot shown, the plane should have traveled about 200 yards, which would leave the flak bursts far behind. Instead they appear above and below the aircraft and then fade away without actually moving anywhere. This is because the filmmakers used a model aircraft for the shot, but neglected to use a fan to blow the air past it for added realism.
In the London WWII sequence, double yellow lines are visible on the road. These were only introduced in the UK in 1956 and didn't become common until the 1960s; a few of the street signs have a style not known before the 1960s.