Continuity mistake: After Hawkeye and Trapper cut the bomb wires, Trapper kneels down to see if it's still ticking, and his hand disappears from his helmet. (00:23:05)
Continuity mistake: Right after Radar tells Henry to forget about the game there's an explosion, and when Radar shouts, "More on the way!" everyone ducks and we see Henry's diploma up on the wall, but when it cuts to a different angle the diploma has vanished before the room even shakes or the heater's stovepipe falls.
Continuity mistake: While Hawkeye holds the tail assembly, Trapper cuts the wires. In the closeup, he cuts the wires a few inches from the connectors. In the wide shot, the wires were cut closer to the bomb's body.
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 ★