Sometimes You Hear the Bullet - S1-E17
Henry Blake: All I know is what they taught me at command school. There are certain rules about a war, and rule number one is that young men die. And rule number two is that doctors can't change rule number one.
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 ★