Everyone Has a Brother-in-Law - S2-E23
Factual error: Schulz repeatedly calls Klink's adjutant "Kapitän." In the German armed forces the rank Kapitän only exists in the Navy, the German equivalent for the American rank of Captain (which is obviously meant here) is Hauptmann or Stabshauptmann.
Reservations Are Required - S1-E15
Character mistake: In this episode, Hogan suggests a helicopter as means for escape from Stalag 13. As a matter of fact, the allies had no helicopters operational before April 1944. The famous R-4 made its first flight only in January 1942. So unless Hogan planned to steal one of the Luftwaffe's 20 FW Drache (a maximum of ten or so existing at any given time) or a whole bunch of the single-seat Flettner Kolibri (24 total built) he was out of luck.
Anchors Aweigh, Men of Stalag 13 - S1-E16
Character mistake: Klink claims that the North Sea is about sixty miles from Stalag 13, in reality however the town of Hammelburg and thus the nearby camp are about three-hundred miles from the North Sea.
Other mistake: Towards the end, the shot of the plane landing is a recycled shot. Even though Klink waved the flashlight, an unidentified person can be seen in the shot waving a signal light in the midst of the field. Klink was by his car.
Continuity mistake: In Hogan's quarters, as he and Critendon are talking, his arms are by his sides, and suddenly crossed. As Hogan goes to get his hat off Critendon's sword, his right hand is shown, then after the angle changes, his left hand draws back with the hat, and his right comes up to grab it.
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.
Factual error: In several episodes, Hogan and his men are confronted with mobile missile launchers. These are depicted as a missile on a flatbed from which it is launched at the push of a button. While there existed mobile German missile launchers for the A4 missile better known as "V2", they consisted of a whole column of trucks, among them a transport truck for the missile with erector hydraulics, at least two tankers for the fuel, a control vehicle and several other trucks full of equipment, not counting the transport capability for a dozen or more operators that were necessary to launch them. Also the missiles weren't launched from the transport vehicles, but placed on mobile launch racks that were transported separately.
Nights in Shining Armor - S3-E8
Other mistake: In Hogan's quarters, after Hogan reveals the two Aces up Newkirk's sleeve, Newkirk goes to brush his hair. As his hand goes up, you can see the cards in his hand.
Continuity mistake: In Klink's quarters, Hogan is complaining about Berger's activities. As he does, he goes to eat a sandwich with his left hand. After the angle change, he has both hands on it.
The Flame Grows Higher - S1-E31
Continuity mistake: At the end, as Schultz and Hogan come out of the office, there is a blank wall, like a kind of foyer. Any shots of the front door from the inside show the door opens directly into the outer office of the secretary.
An Evening of Generals - S3-E13
Revealing mistake: The silver rack with bowls starts moving a second before the rocking explosion.
An Evening of Generals - S3-E13
Continuity mistake: As Klink is listening to Burkhalter, he is gesturing with a blue pencil. A second later, it's yellow.
An Evening of Generals - S3-E13
Continuity mistake: As Klink is listening to Burkhalter, his right hand is on the desk. A second later, it's at the top of his chest with his left, holding a pencil.
Revealing mistake: LeBeau hands Schultz the pan straight from the hot plate, but Schultz puts at least three fingers around it while eating without any apparent issues. Note that LeBeau earlier said the Crepe Suzette were "not quite ready yet" - or in other words, still cooking. (00:01:40)
Revealing mistake: After the cell door blows, you can see the fuse of the stick of "dynamite" Newkirk placed still burning on the ground. Since the dynamite would blow when the fuse is burnt up, that literally can't happen. (00:22:40)
Continuity mistake: In the tunnel, Hogan lays out the plan. The arms of the man next to him goes from crossed to by his side between angles.
Continuity mistake: As Schultz is addressing the formation after taking command, his swagger stick switches from his right hand to under his left arm after the camera angle changes. Also, a minute later, Carter goes from being beside Newkirk to being in front of him and back again in a few seconds.
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.
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.
Continuity mistake: After Newkirk photographs the blueprints, he loosely rolls them up and goes to hand them to Carter. A second later, they are tightly rolled with a rubber band around them.
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