Doonesbury by Garry Trudeau for February 01, 1972
Transcript:
B.D.: I talked to the army recruiter today because of my R.O.T.C. experience, I can leave for Vietnam on Saturday... Mike: B.D., this is crazy. Why on earth do you want to go to Vietnam? B.D.: I'm glad you asked. I made out a list of the reasons why. Mike: "I am going to Vietnam a) for mom, b) for apple pie, and, c) so that my roommate Mike can grow up strong and happy in a great land free of communism and tyranny." I'm touched. B.D.: Naturally.
I think was referring to making his mom proud rather than to her nationality.