Factual error: Many of the prisoners are wearing watches, which is incorrect. Upon arrest a prisoner's watch was confiscated. This prevented them using them to bribe or barter with corrupt guards (and as this film acknowledges, there were plenty of those) as well as making coordination of meetings or escape plans difficult.
Factual error: A convoy of open trucks arrive at the camp bringing the latest batch of prisoners, many of whom are carrying rucksacks and tote bags of clothing and other possessions. Where did they come from? Combat servicemen in World War Two did not carry overnight bags with them - a change of clothes or a handy supply of toiletries was the least of their concerns. A prisoner of war arrived in the camp with the clothes he stood up in and nothing else.
Factual error: Why is Hilts not wearing a uniform? A serving officer captured behind enemy lines in civilian clothing risked being shot as a spy. If a prisoner's uniform was too worn or damaged to wear, it was routine for the German authorities to replace it - a P.O.W. in civilian clothes is an obvious escape risk. He is wearing a pair of tan chinos and a cut off sloppy Joe sweatshirt, both ridiculously anachronistic - Sixties hipster fashions - and nowhere even close to a World War 2 uniform.
Character mistake: The scene in the outdoor Parisian cafe is incredibly daft. First, the cafe owners call James Coburn's bizarrely-accented Australian to the telephone to keep him out of the way as their accomplices assassinate three uniformed German officers seated in the cafe in a drive by shooting. They then toast the killings with cognac, and that is the mistake - not the shootings, not the luring away of Coburn - the mistake is that the cafe proprietors celebrate the assassination of the German officers in broad daylight, in the open, without even stopping to think that such an action would have them shot, because all of this is done in the direct view of passers-by in broad daylight. Do they think those three German officers were the only ones in Paris? How did they know Coburn wasn't an undercover Gestapo agent or a French collaborator? Don't they stop to consider that in an occupied city machine gun fire is going to draw some attention from the authorities, who might just wonder what a couple of bullet riddled corpses are doing lying about the place?
Visible crew/equipment: In the scene where everyone is lining up to receive the moonshine that the Americans made you can see a crew member on the left hand side. He is wearing a red baseball cap and modern clothes. He is motioning for the extras to go into the main shot to get the alcohol. (Widescreen edition).
Continuity mistake: Check out the memorable scene when Hendley and Blythe, trying to reach Switzerland in a stolen training aircraft, fly over marvellous Castle Neuschwanstein. According to Hendley, they've almost made it, just 20 minutes of flight and one mountain range left to cross. This is quite funny because the Neuschwanstein shot reveals that they're actually flying straight in the wrong direction. The camera faces south, the plane moves from right to left, meaning they're heading east, straight away from the Swiss border which is just 50 kilometers west of the famous castle.
Revealing mistake: Towards the end of the film, when Hilts (Steve McQueen) is in a motorcycle chase with the German guards, if you watch closely, when the camera cuts away from Hilts and to the German motorcyclists, you might be able to notice that one of the guards chasing McQueen IS actually McQueen! They used him to play one (or maybe more) of the guards because of the experience he had with motorcycles. This can also be seen in some behind the scenes footage on the DVD version of the film.
Continuity mistake: When Hendley and Blythe emergency-land their plane, it dashes into a copse. Both wings are cut off by trees and stay behind, while the fuselage runs on for several meters, finally coming to a halt with the tail facing down and the cockpit up. Next shot (pilots exiting the plane), the crash site looks very different: The tail now points into the air, cockpit down. And even worse, the wings have returned to the plane, I mean they are still cut off, but now positioned neatly on both sides of the fuselage instead of all those meters behind where you'd expect them.
Continuity mistake: In the scene in which the POWs are distributing the tunnel dirt over the compound, Hendley is leading a group of POWs in a soldier's march. In one shot, dirt is coming out from the bags inside their trousers, but their hands are visibly swinging back and forth; they can't be pulling the strings in their pockets to release the dirt. (00:53:50)Cubs Fan
Continuity mistake: When Hilts and Ives are put back in the cooler after their first escape attempt, the dirt on their faces in the corridor outside their cells doesn't show up in the same places when they are actually in their cells.
Plot hole: Roger's initial briefing at the beginning of the film states that 'Tom' goes out from 104 and 'Harry' from 105. Despite this the goons are said to be in 105 when they find the entrance to Tom.