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 mic 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.
The Kamikazes Are Coming - S6-E20
Revealing mistake: As the rocket blasts out of the recreation hall, the guide wires for the model are visible.
Factual error: The first episode of Hogan's Heroes (Season 1) begins with a view of Stalag 13 and a title: "Germany, 1942." That said, Colonel Hogan indicates in several episodes that he has worked in the Pentagon although construction of the Pentagon was actually completed in 1943.
The Kamikazes Are Coming - S6-E20
Other mistake: As Marya comes out of camp office, the seams between the sections of the studio flooring are visible at the bottom of the shot.
Klink for the Defense - S6-E19
Visible crew/equipment: As Newkirk and Hogan enter the office, the shadow of the boom mic plays on the wall.
That's No Lady, That's My Spy - S6-E17
Other mistake: The Kommandant's building and the barracks appear to be only twenty to twenty-five feet apart, showing that this scene of Roll Call is in the studio. Otherwise, the outdoor shots are at the studio back lot.
Revealing mistake: In the close ups, Professor Bauer's spectacles do not have lenses.
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.
Other mistake: As Schultz talks to Burkhalter, it sounds like he says Captain.
Visible crew/equipment: As Schultz calls for attention, the studio lighting is reflected in his monocle.
Factual error: As the staff car comes up the street, there are a number of neon signs lit up, as well as store fronts. This is wrong as during the night in wartime Europe, such lighting would be dark to avoid night bombing.
Other mistake: As Hogan and Kinchloe sit on the bunk to keep the trap door from opening, the secret switch to activate it is visible.
Answer: Nimrod's actual identity was never revealed in the series. It was only known that he was a British intelligence agent. Nimrod was not Colonel Klink. Hogan had only implied it was him as a ruse to get Klink returned as camp commandant, not wanting him replaced by someone more competent who would impede the Heroes war activities. The term "nimrod" is also slang for a nerdy, doofus type of person, though it's unclear why that was his code name.
raywest ★
"Nimrod" is originally a king and hero mentioned in the Tanach and taken into the Bible and the Koran. His name is often used in the sense of "stalker," "hunter," and sometimes figuratively as "womanizer" as in "hunter of women." I've never seen it used to denote a nerdy person, and although I cannot disprove that connotation, I think given his role, the traditional meaning is more likely the intended one.
Doc ★
It's widespread enough that Wikipedia has an entire section on it: https://en.wikipedia.org/wiki/Nimrod#In_popular_culture