Continuity mistake: In the mess tent, when Frank asks Hawkeye why he makes his life so miserable in the OR, notice that in the wideshots there's a silver pitcher, napkin holder, etc. On the table between Trapper and Margaret who are facing each other, but in the shots facing Margaret and Frank, and also Trapper and Hawkeye all of those things vanish and then reappear.
Revealing mistake: When Frank is digging for gold, he has 2 shadows. (00:20:00)
Other mistake: While the dentist is working in Henry's mouth Frank's describing Hawkeye and Trapper's pranks, and right after we see a shot of the dog licking hamburger from Frank's ear, when it cuts to Henry saying, "Frank, just leave my married life out of this. Doc, will you watch it before I swallow your watch!" keep your eyes on Larry Linville as he mouths McLean Stevenson's lines along with him.
Other mistake: While celebrating the ceasefire, a Jeep full of people including Father Mulcahy stops between the Swamp and the main building. There's a streamer hanging down either side of Mulcahy from above the top of frame. Unless there's a power line to the Swamp that never appears at any time, there's nothing for it to hang from.
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 ★