Revealing mistake: When Hilts is first locked in the cooler he turns to verify the door is locked. Apparently the set wall was so flimsy the stage hand seen on the left was required to hold the wall as Hilts pushed the door, to prevent it from moving. The stage hand looks like the German guard without his rifle.
Factual error: The entrance to tunnel Dick is shown improperly; the trap door was on the side of the drain basin, not the bottom. This was discussed in the Brickhill book, and subsequently verified by research on the site (shown on the US television program NOVA) which found the original door and its lifting handles.
Continuity mistake: When Hendley and Blythe get into the German aircraft first, the cockpit is tiny and cramped, like you'd expect. However, when they cut to the studio-done flying scenes, it suddenly becomes much larger, nice and roomy.
Revealing mistake: When McQueen is jumping the fence on the motorcycle, it can clearly be seen the machine used for the jump is in fact a modern offroad model, with long travel suspension, in camouflage guise.
Revealing mistake: In the scene where the goons find 'Tom', the water that is poured down the hole is not steaming, even though the water burnt his hand.
Continuity mistake: In the scene involving Hilts and his baseball directly after Sedgwick and Haynes have their sham fight, Hilts drops his canvas bag with his name on it on the ground. When Goff comes to join Hilts, however, the canvas bag is nowhere to be seen. Despite the angle it would have been seen as the bag was placed down horizontally. (00:13:35)
Other mistake: When the three Americans invite the British to join their 4th of July celebration, Hilts plays the flute with his right hand the wrong way round on the instrument.
Continuity mistake: In the scene where Hilts is first locked in the cooler, he is eventually let out. It shows him walking out from a view that is inside the cooler, and his coat is on one arm (I forget which arm it is). Then it shows a view from outside of the cooler,of him walking out, and his jacket is on the other arm. He didn't switch it while walking, because the clip is about 2 seconds long.
Factual error: In the scene at the railway station, the carriages bear the 'DB' logo of the Deutsche Bundesbahn which is definitely post-war. During the war they would have carried the Deutsche Reichsbahn logo.