In one scene taking place in a German laboratory, a periodic table of elements is hanging on a wall. It shows all the 103 elements known to science in the 1960s, but during the war, fewer than 92 elements were known: the rest were created by nuclear science, including several instrumental in the top-secret Manhattan Project.
On numerous occasions Eva Braun, Hitler's mistress, is mentioned either by Hogan's men or the Germans. Braun's association with Hitler was a closely guarded secret only known to Hitler's inner circle, and whose existence wasn't revealed until after the war.
In "The Scientist", Carter states that he can't teach LeBeau any chemistry because he ran a drugstore, not a chemist's shop. But in the earlier episode "German Bridge Is Falling Down", he knew how to make explosive chlorine gas out of ammonia and bleach, and in the later episode "Hogan Springs", he mixed up a convincing batch of "mineral water" with no difficulty.
During the opening credits, an African American prisoner is lined up to Hogan's left. When the shot changes and shows "Starring Bob Crane" the same prisoner is now in the row behind Hogan immediately behind his original position. In addition Hogan is lined up on the far right of the line in the opening shot with a prisoner immediately behind him. In the next shot there is nobody behind him and there are prisoners to his right in both rows.
The palms of Los Angeles are clearly visible in the treeline around Stalag 13 in some episodes. Date palms can be seen in outdoor scenes in 'The Well' for example. Very few palms grow outdoors in Germany, if any. Helps to use HD TV, I never would have seen this on the old B&W analog set.
The Gestapo did not wear black uniforms as seen in Hogan's Heroes. While it was certainly a nice touch of artistic license to differentiate the more sinister Gestapo like Major Hochstetter from the relatively benign Luftwaffe guards, this type of black uniform was a ceremonial uniform seen mostly on the guards at important buildings or at state functions. The appearances by the Gestapo in plain clothes and a Nazi party tie pin are closer to the truth.
Throughout the series, all vehicles have Army license plates (WH, i. e. "Wehrmacht/Heer"). The vehicles from Stalag 13 should have Air Force license plates (WL, i. e. "Wehrmacht/Luftwaffe"), as it technically is an Air Force unit.
The Germans usually address each other by the U.S. equivalent of their ranks. Sergeant Schultz's rank is "Oberfeldwebel". Colonel Klink is "Oberst". Captain Gruber is "Hauptmann". The Gestapo and S.S. had their own rank system, which was different than the traditional military rank system, so Major Hochstetter should not be called 'Major'.
In numerous episodes Hogan and his men contact a submarine by radio. The sub is always shown submerged. Only Ultra Low Frequency (ULF) radio waves can be heard under water and these were not invented until after the end of the war.
Group Captain Crittenden (incorrectly ranked Colonel) wears an incorrect cap. Group Captains in the RAF wear a cap that has a patent leather peak, and one row of gold oak leaves on the peak. The cap he wears is worn by officers only up to the rank of Wing Commander.
Throughout the series, interior doors always have round door knobs. American doors usually have round door knobs. German doors almost always have a door handle (die Türklinke) rather than a round door knob.
The RAF Corporal wears an incorrect cap. The cap he wears is a US style 'Garrison Cap'. He should be wearing a 'forage cap' whilst similar, has different shape and stitching. The garrison cap has 2 buttons on the front, which have been added to make it look like a forage cap. Garrison caps don't have buttons on the front.
Numerous episodes have Gen. Burkhalter appear at Stalag 13 and boss Col. Klink around as a direct superior would. Burkhalter is a Wehrmacht officer and Klink is a Luftwaffe officer, so they should have no contact, especially considering the well-known tendency of the Nazi military branches to resist consolidated command and operate with near-complete independence of one another.
The Heroes have trap doors in various places. The door in Klink's quarters is under the stove and when they open it the stovepipe is shown hooked to an opening in the wall. However, when they hide a door under a sink, there is no drain opening visible when they open the door and the bottom of the door is smooth and unbroken.
The uniform the RAF Corporal wears is also incorrect. It appears to be a US issue 'IKE' blouse with a very short tab at the waistband. The correct British issue battledress blouse would have a longer waist tab ending with a flat buckle on the right front hip.
Sometimes you see the warning "Gebrauch keine Haken" on boxes in the background. This is a literal translation of the English "Do not use hooks" and would never be written in that form on a German box. Correctly it would have to be "Keine Haken verwenden".
In many episodes something is dropped to the heroes by parachute. In almost every case when "something" leaves the plane it is obvious that it is a person since a pair of legs is clearly visible, yet usually when it comes down it is a box or some other container.