The film is called Der Fuehrer's Face and is set in Nazi-land, a place where the clouds and trees are shaped like swastikas and the houses look like Hitler. Caricatures of German government officials, such as Joseph Goebbels and Benito Mussolini, are seen marching through the streets singing praise to the Nazi regime.
A Nazi Donald Duck is then awakened, fed a severely rationed breakfast and made to read a portion of Mein Kampf while sitting under Hitler’s portrait. Donald then goes to work in a factory, where he makes shells on a conveyer belt and salutes Hitler as portraits of him pass by.
Donald then starts experiencing some hallucinations, which then collapse away to reveal it was all a bad dream. The movie won the Best Short Film award at the 1943 Academy Awards and remains to this day the only Donald Duck film to do so. The main song in the film has also been covered multiple times. You can watch the film below, but be warned, you will never be able to think of Donald Duck in the same way again.