If you don't recognize this opening in the first couple of minutes you need to watch this film (either again or for the first time).
Click read more below for a bit more commentary.
This clip is from Francis Ford Coppola's masterpiece "Apocalypse Now". In a span of a few years, Coppola directed "The Godfather I and II" and "Apocalypse Now", and also produced George Lucus' breakout film "American Graffiti". Talk about artistic innovation. To actually create Apocalypse took incredible vision and perseverance. The film was besieged by problems "including typhoons, nervous breakdowns, the firing of Harvey Keitel, Martin Sheen's heart attack, extras from the Philippine military leaving in the middle of scenes to go fight rebels, and an unprepared Marlon Brando with a bloated appearance (which Coppola attempted to hide by shooting him in the shadows). It was delayed so often it was nicknamed Apocalypse When?." ( Wikipedia )
Drug use was also rampant among cast members. In this famous scene with Charlie Sheen, Sheen was so wasted, he could hardly stand: