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).
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.
Continuity mistake: The boxes being carried into the buildings in the beginning of the episode were about sixteen inches high by three feet long. When the bomber plane is dropping bombs, what drops out is a lot bigger than the dimensions of the boxes.
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. (As another contributor previously posted, the term "nimrod" is slang for a nerdy, doofus type of person, though it's unclear why that was his code name).
raywest ★