When escaping from the office, Errol Flynn's character stuffs the same bundle of documents into his coat twice, once in a medium shot, and again in the wide shot.
On a bombing run the bomb bay doors are open then there are alternate shots of a German ack ack unit but in two shots of the plane the bomb bay doors are closed. After dropping the bombs the bay doors are closed then open and then closed again.
Near the end of the film where the three escapees board the captured British plane, they are attacked by the Germans. Flynn enters the gun turret, rotates it to sight the enemy then opens fire. When Reagan pulls his injured mate into the plane and closes the door, he relieves Flynn who goes forward to start the engines and fly out. Before this happens, Reagan again rotates the turret and fires on the Germans.
Rotating the turret and firing the guns was worked by hydraulics which were only operable with the plane's engines running.
At the beginning of the movie when the crew is starting engines, the aircraft shown is a twin engine Lockheed Hudson.. they show the engines starting twice to give the impression it is a 4 engine Boeing B-17 - which is what the crew is supposed to be flying.
When identifying themselves on the flight home they say plane markings "TK". While on the ground the marking was clearly "T".
After crashing the crew board a train which is obviously American as it has a light in the centre of the front of the smoke box. and a typical American box car.
The same shot of a railroad area being blown up is used twice, once to depict the site blown up by the saboteur at the beginning, and soon after as the area being bombed by the RAF bomber plane.
In at least one shot of the bomber in flight, the strings holding up the model are plainly visible.
At the beginning of the movie, when the truck is carrying the crew out to their bomber, the engines are running. After the crew is belted in and checked the aircraft commander has co-pilot start the engines.
The German steam locomotives and rolling stock are clearly of North American design.
The closing shot of the bomber flying back over the Channel toward England shows the plane heading into the sunset, which would indicate the sun was setting in the north.
Escaping in a German captured Hudson the crew head for the channel and England. Johnny drops a large bomb, a close aerial shot of a group of buildings is seen, the centre one of which blows up. Forbes asks Johnny if he'd dropped the bomb to which Johnny replies'Yes onto a battery of guns that were shelling Dover'. Not only were no guns seen in the aerial shot but not even any water indicating that they were no where near the Channel.
At the end of the film as the plane is taking off two cars, a small white sedan and a black one immediately behind it, can be seen buzzing down the highway adjacent to the end of the runway.
German troopers throughout the movie are wearing the clunky WW1 era M-16 helmet, which had become obsolete in the German Army long before WW2 came around, having been replaced by a much sleeker and lighter model.
While the men are walking through a swamp and Kirk is describing how much food he scrounged during the First World War, his words clearly don't match his lip movements.
Early in the movie as the crew is going through their pre-flight checklist the pilot tells the co-pilot to start the port outboard engine. Instead, a clip of stock footage of a starboard inboard engine being started is erroneously inserted.