Other mistake: When the Colonel Griswald of the 1st Cavalry goes to leave camp, the Jeep he gets in is marked "4077 MASH" on the bumper instead of 1st Cav.
Other mistake: As Burns, driving the tank, runs over the Swamp, there's no sign of the still anywhere.
Answer: The C-42 was a military variant of the Douglas DC-2. Very few C-42's were built, so it's questionable that Potter would specifically have seen that particular model, but, given his military background, it's not entirely unreasonable that he might use the military designation even when the aircraft in question is actually a civilian DC-2.
Tailkinker ★