Part of Hogan's plan requires Sgt. Kinchloe to impersonate a Gestapo General over the telephone. The Gestapo was a civilian police organization that did not have military ranks.
The truck that Hogan drove to STALAG 4 and back had the steering wheel on the right side. German trucks had the steering wheel on the left side.
When Schultz and Hogan go to pick up Carter, LeBeau, and Newkirk, there is a sign reading 'Luft-Stalag 4' under the 'Kommandantur' sign on the outside wall of Major Bernsdorf's office. There is no corresponding 'Luft-Stalag 13' sign on the outside wall of Klink's office. For a branch of the military, signage of this nature would be a standard for all Luft-Stalags - either there is a sign there, or there is not. The obvious reason for the existence of the sign is to identify the re-dressed Stalag 13 office as being the office of the Kommandant of Stalag 4.
When Schultz dressed as Klink goes to STALAG 4, he does not seem to know Major Bernsdorf, and Bernsdorf does not know him. In reality, all of the STALAG Kommandants should know each other.
In the introduction, when Newkirk pushes the plunger on the detonator, it practically falls in as if there is no resistance. The teeth visible on the stem are supposed to engage a gear, which turns a small generator to create an electrical pulse. The pulse runs down the wires to the blasting caps, which actually set off the dynamite. As easily as Newkirk pushes the plunger, and as light as it appears to be when he carries it around after the explosion, it is obvious there is nothing in the box.
When Schultz was wearing the monocle impersonating Klink, he wore it in his right eye. Klink wears the monocle in his left eye.