Trivia: Marlon Brando (Colonel Walter E. Kurtz) showed up to the set 50 pounds overweight and admitted that he had not even read the script yet. Brando demanded that he be shot only in shadow and that his scenes be almost entirely improvised. He said he did this because he didn't want to work as hard. Francis Ford Coppola has not worked with Brando (who has a notorious reputation for being a difficult actor to work with) since then.
Trivia: The scene where Colonel Kilgore offers his canteen to the wounded Vietcong is based on a real incident. The army officer really did say, "Any man brave enough to fight with his guts strapped to him can drink from my canteen any day". (From Hearts of Darkness: A Filmmaker's Apocalypse).