Other mistake: Just after the Royal Navy destroyer has sailed through and depth charged the area where the British survivors are, there is a shot of the churned up sea with sombre music playing, and the seagulls are flying backwards.
Other mistake: When Hoffy goes to blow out the single candle used to light the room, there's an extra second of light before it gets dark. Also, there's too much light to be explained by one candle, and no electric lights (The Germans would have cut the lights off from outside).