Visible crew/equipment: After Hawkeye shows up in Colonel Potter's office with severe allergy symptoms, BJ and Margaret walk out with him, and when Potter says, "Time we found out what's on his mind," the shadow of the boom mic moves across the door.
Visible crew/equipment: A crew member is visible in Margaret's tent when she confronts OR nurse Helen about her drinking, approximately halfway through the episode.
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 ★