Revealing mistake: During the main part of the plot, the guys are putting dynamite on each truck in the convoy as they fuel up at Stalag 13. It is supposed to be dark, (hence the reason the boys wear black) but there are shadows as if it were day. It's impossible for the driver in the following truck and the guard in The Tower to miss seeing the boys as they go back and forth to plant charges.
Revealing mistake: The first shot of the train the view is normal. Then after Lebeau starts in reverse you can see the smoke trail going in the wrong direction. The final shot shows the train moving in reverse, but notice the smoke trail is going to the rear of the train instead of the front as it should be, since it's moving in reverse. (00:15:05 - 00:22:25)
Revealing mistake: When the homing bomb hits Burkhalter's car because Klink used the radio, you can see the mini tank from "Tanks for the Memory" (s2e9) sticking out of the wreckage.
Revealing mistake: The bunk that is the entrance to the tunnels appears to be moving upward about a split second before Newkirk taps the hidden key to activate it.
Revealing mistake: As the building is being prepared for the upcoming event, and men are going in and out, as Shultz goes to report to Klink, look past him and the roof behind him. You can see the studio water tower in the distance.
Answer: It's a solitary cell. Steve McQueen, star of 'The Great Escape' is known as the 'Cooler King'.