Dr. Seuss, Chuck Jones, and Mel Blanc's US Army cartoon warning against loose lips (1943)

Private Snafu was the US Army's series of instructional cartoons from World War II, written and/or directed by the likes of Theodor "Dr. Seuss" Geisel, Chuck Jones, and PD Eastman. The voice of Private Snafu is performed by Mel Blanc (Buggs Bunny, Daffy Duck, etc.). In this episode, written by Dr. Seuss and titled "Spies," Private Snafu learns a military secret but he can't seem to keep his lips sealed. Note the grossly racist depiction of an Asian man, sadly typical of the era.