Corrected entry: While Klinger is collecting toilet paper from the latrines, he's singing/chanting the theme music from "Bridge on the River Kwai" (known as the Colonel Bogie March, BTW). That movie wasn't released until several years after the war.
Correction: The famous march whistled by the POW in the movie wasn't composed for it but is actually the "Colonel Bogey March" composed in 1914 by Lieutenant F. J. Ricketts. It became immensely popular with the troops in WW2, with the somewhat rude text "Hitler has only got one ball." This is also the reason why it was whistled in that movie, because those lyrics wouldn't have gotten past the censors. That it is often (wrongly) called the "River Kwai March" today is due to the fact that the actual movie theme called that was a march superimposed on the whistling POW in the movie. So when you're listening to the movie theme, you're actually listening to two marches: Col. Bogey March, and the River Kwai March at the same time.
Corrected entry: When Hawkeye and Radar are talking to the recon men, an explosion goes off behind them, with no sound of the incoming shell.
Correction: The music itself was written during World War I and was associated with soldiers during both World Wars. Klinger would have been familiar with it before the release of the film that kept it famous.
jle