Continuity mistake: All through the episode, we are in a snowy, wintry camp surrounded by hills and trees. The target Gen. Burkhalter points out however is a little shed on a flat-as-a-board prairie with not a flake of snow OR a single hill visible anywhere, and the brown grass of late summer. (Yes I noticed there are some mountains off in the distance. So not relevant for this mistake).
To Russia Without Love - S6-E18
Revealing mistake: As the motorcycle and the side car split apart and drive around independently, you can see that the side car has been given two extra wheels, and some other stuff underneath as well that's not present on regular Wehrmacht BMW sidecars - probably a remote control of sorts. Also, the motorcycle Schultz rides has training wheels mounted in the shot where the side car comes off.
Factual error: Frankel suggests manipulating the missile's gyroscope, and Hogan suggests an electromagnet as means to do it, which is later implemented. Gyroscopes however are not affected by any magnetic force, which is what makes a gyroscopic compass superior to a magnetic one in many situations. To enhance that effect, gyroscopes are deliberately built out of materials with as little magnetic susceptibility as possible. A large electromagnet next to the missile could potentially cause all kinds of havoc with all kinds of parts of the missile guidance and control, but the gyroscope itself would not be among them.
Other mistake: When the Heroes are outside talking, the camera focuses on Col. Hogan. Over his right shoulder you can see a hill with a baseball field's home plate fencing on top.
Factual error: The motorcycle courier coming in wears sunglasses that are definitely newer than 1942. Sunglasses with domed, wrap-around lenses were not invented in the 1940s.
Kommandant of the Year - S1-E3
Factual error: A sharp brass cone has been put over the spike on Klink's Pickelhaube, so Hogan can pin the page torn from the Geneva Convention onto it. The real spike of a Pickelhaube has concave slopes, and it isn't pointy enough to pin a piece of paper onto it.
How to Catch a Papa Bear - S4-E3
Factual error: In the tunnel Hogan loads a magazine into a US issue .45 pistol and points it at Myra, but he never chambered a round and didn't cock the hammer on the pistol. The .45 pistol in WW2 was single action. For a single action pistol to fire, a round needs to be chambered and the hammer has to be cocked manually before the trigger is pulled and the pistol to fire. (00:22:00)
Colonel Klink's Secret Weapon - S2-E28
Continuity mistake: During the inspector general's visit, Le Beau and Newark fall out with switched hats (i.e. Newark is wearing Le Beau's red hat and vice versa). In the next shot when in formation, they are wearing their own hats. (00:21:00 - 00:22:00)
Audio problem: Hogan knocks out his pipe against the Prussian helmet on Klink's desk. It makes a tinny, metallic sound. The Prussian Pickelhaube was made from compressed leather, not metal.
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.
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?
Is There a Doctor in the House? - S3-E18
Continuity mistake: Hogan pulls a container with a red cross out of the drop box and opens it. It is labeled "penicillin" inside and contains among others several vials of clear liquid. Back in the camp, Hogan gives a box with a red cross on top to Kinchloe, saying "here's the penicillin." It is a completely different box.
Axis Annie - S3-E23
Factual error: After Carter realises Hogan got the envelope off so fast, Newkirk says "Speedy Gonzales." 'Hogan's Heroes' was supposed to take place from 1942 to the end of the war. Speedy Gonzales first appeared in "Cat Tails for Two" in 1953.
How to Win Friends and Influence Nazis - S3-E7
Visible crew/equipment: When Hogan gets up in the hotel room they're all in, the shadow of the boom mike plays on the wall he heads toward.
Continuity mistake: LeBeau and Newkirk are on a building roof and the Nazi flag is blowing in the wind with great force. In the next shot a guard tower is shown with a Nazi flag that's hanging straight down and not blowing at all. (00:01:00)
The Great Brinksmeyer Robbery - S2-E18
Continuity mistake: As Kinch answers the question about the radio, he's in quarter profile to the locker with his shirt open. After the cut to a wider scene happens, he's turned toward the camera, and his shirt is half buttoned.
Visible crew/equipment: When Le Beau signals the plane, the camera crew is reflected in the flashlight.
The Battle of Stalag 13 - S2-E5
Visible crew/equipment: As first Feldkamp, then von Kattenhorn, get in their respective staff cars, the camera crew and equipment is reflected on the doors and glass.
The 43rd, a Moving Story - S1-E23
Revealing mistake: As Carter and Newkirk sit by the wall catching their breath, a seam can be seen running vertically where two wall sections meet behind them.
Answer: It's a solitary cell. Steve McQueen, star of 'The Great Escape' is known as the 'Cooler King'.