Revealing mistake: Whenever there is a shot of the outside of the barracks, where it can be seen that it is outside on the studio lot, look at the "snow" on the roofs. Most of the time, it appears to be just paint in the shape of snowdrifts.
Revealing mistake: Every time they go to destroy a truck convoy, you can see that it is a miniature set with model trucks blown up, and it is a re-used shot every time. Same goes for the trains that get blown up.
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