The Vanishing Private (1942)

Private Duck is a camouflage painter. He paints a giant cannon with some very gaudy colors, until Sergeant Pete explains that the point is to make it so the cannon can't be seen. Donald finds a bucket of experimental invisible paint and makes the cannon disappear. Pete isn't happy with this, and knocks Donald into the paint, then chases him, until he runs into the general. As Pete tries to explain, Donald prods him with a cactus, then goes off to steal some pies. Eventually, Pete goes berserk and starts throwing grenades willy-nilly and gets in more trouble with the general.