Donald Duck was Disney's star, moreso than Mickey Mouse. The angry little duck was easily the most popular character Disney had going for a long time, especially during the war. Commando Duck, one of Disney's numerous war propaganda cartoons, followed Donald through basic training in the Army and right into his first mission: he's to single-handedly take out a Japanese base.
Enter: the Japanese caricatures. They first appear hidden in a tree and behind a bush as two snipers who get into each other's way, and then, because of the belief that Japanese people were overly polite, continually apologize to each other in English. Once Donald turns around, a sniper informs his crew that it's "Japanese custom to always shoot a man in the back."