Audio problem: When the quartet plays, Klink's bow strokes don't match the music. That is all the stranger since Werner Klemperer was a proficient violinist. Maybe his playing wasn't bad enough on the stage recording?
Revealing mistake: As the truck passes Carter and Newkirk, it's easy to tell they're hiding behind tarp-covered boxes rather than the greenery or rocks around them.
Revealing mistake: The film is flipped as the swastikas on the Gestapo uniforms of Hogan's men are reversed.
Factual error: Hogan calls the radio detection truck "radar" when he orders the SS guard to switch it off. From other episodes, we know that Hogan knows what radar is, and back then, the difference between radio homing equipment and radar was even clearer to people than it is today, because radio homing was an established technology, while radar was brand new, and most people were not even aware it existed.
Factual error: Baker picks up a lot of static in his radio, then suddenly signs off and says "Sounds like the radio detection unit picked up our signal." Unlike radar, radio signal homing relies entirely on measuring the signals emitted by the transmitter that is tracked. It works by comparing the strength of the signal arriving at each component of an array of directional antennae. The process is completely passive and does not cause any alteration of the signal measurable at either receiver or transmitter at all, and certainly not any audible interference or humming.
Other mistake: The place the car ends up on the porch is where the wooden steps would have been. But there is no debris from the destroyed steps, meaning they were removed for the gag.
Other mistake: As the camera looks at the now-crashed car, the position and condition it is in is impossible. Though funny, there is no way the car could have jumped up on the porch as shown. The front would have been crushed in, the wood of the porch damaged. The interiors of the doors are impossible given that the car would have been kept in an immaculate condition.
Revealing mistake: As the camera looks at Schultz driving the car, even though he's moving in the seat, you can see through the back glass the car isn't moving at all.
Visible crew/equipment: As Schultz drives away from the boys, the camera crew and equipment is reflected in the window.
Other mistake: When Carter goes to switch the full cup for the empty one, he accidentally sloshes water on Newkirk's hand and the fan of cards in it. When Carter goes to move the cups, look at Newkirk's hand. The cup exchange happens in front of the hand. The hand is out of range of the water.
Audio problem: When Hogan is taking pictures of Shultz in front of the halt-track (really, getting shots of the control panel), in the second photo, the shot is shown as if it's Hogan looking through the camera. He starts on Shultz's face, but pans down and to the right to get the control panel. Just as the view gets on the panel, you hear the shutter click, just before the camera fully settles on the panel.
Revealing mistake: When the guys are by the half-track keeping Shultz busy, if you look just above and to the left of Shultz's head, you see some tall fencing at the top of the hill in the distance. From the set up, if appears to be a baseball field outside of the studio property.
Revealing mistake: When the men are in the yard during their exercise period playing football, there is a wide shot of the yard. The half-track is to the left of the screen with Shultz next to it. If you look above the barracks, the Desilu water tower and a large metal building, possibly a studio building, can be seen.
Other mistake: In the end of the episode, after LeBeau said "Hit the deck!", the camera looks to the half-track. According to the plan, there was to be a nitro charge inside it to blow it up. Watch the tarp toward the front. It twitches upward in response to a small explosion on the ground, rather than inside. The sound effects complete the illusion.
Visible crew/equipment: When Major Hochstetter's car arrives at Stalag 13, it drives towards the camera. The shadow of a crewman's hand raised to stop the car is visible on the ground. (00:16:40)
Revealing mistake: In the close ups, Professor Bauer's spectacles do not have lenses.
Other mistake: Baker goes to tap the rectangular spot to open the trapdoor, not only does he hit it once rather then twice, but it sticks in the pressed position. A moment later, Hogan hits it, but it stays in the pressed position rather than popping out. The sound of the pressing is played, but the button doesn't move.
Factual error: Klink and Hogan sit behind each other in the P-51 they try to steal. The P-51 is a single-seat airplane, the only twin-seat P-51 are trainers. A trainer would not be at the flight line with the regular airplanes, and if a trainer would actually scramble with the others, it would at least arouse suspicion.
Continuity mistake: Hogan and Klink are asking Schindler/Brewster about a diversion at the airfield. Brewster has both hands on the coffee cup until the angle change, when his left hand is suddenly out of his pocket.
Answer: It's a solitary cell. Steve McQueen, star of 'The Great Escape' is known as the 'Cooler King'.