Nurse Doctor - S8-E7
Revealing mistake: While Charles is in the shower stall Hawkeye and BJ take his bottle of Vichy water, and when Charles steps out of the stall The Nurses outside the tent whistle, but we can see through the stall's openings that Charles is wearing something.
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 ★