Underground, black-and-white, 16mm animated short put together in 1968 for the Angry Arts Festival by Lee Savage in collaboration with Milton Glaser (perhaps best know for the I ♥ NY logo). It features Mickey Mouse (without a tail), who joins the army, goes overseas and winds up with a bullet in his head.
According to Glaser, “Mickey Mouse is a symbol of innocence, and of America, and of success, and of idealism — and to have him killed, as a solider is such a contradiction of your expectations. And when you’re dealing with communication, when you contradict expectations, you get a result. … There was some talk about Disney suing us, but I think the consequence of that — everybody realized — would have been negative for Disney and would have no benefit. And obviously no profit was made out of the utilization of the character or the film, so nothing ever happened.” (Cory Doctorow, Boing Boing, June 22, 2013).
Note: Although Mickey Mouse in Vietnam is not an official Disney release, during WWII Disney did officially release some war-related shorts featuring Donald Duck, including “Der Fuehrer’s Face” (1942), an anti-Nazi propaganda film (won Academy Award for Best Animated Short Film), Donald Gets Drafted (1942), The Old Army Game (1943), and Commando Duck (1944).