Early in the movie, Captain Willard peers through the blinds of his Saigon hotel room, and says: "Saigon...shit!  I'm still only in Saigon!"  Captain Willard "wanted a mission."  And "for my [his] sins they gave me [him] one.  And when it was over, I'd [he'd] never want another."  

There could not have been a better song choice for the intro portion of Apocalypse Now than The End by The Doors.  First of all, The Doors epitomized the madness, the cultural and generational tension, of 1960s America.  Not the Beatles.  Not the Rolling Stones.  Not Jimi Hendrix.  No, it was the sound of The Doors and the voice of Jim Morrison that in effect became the American soundtrack of this tumultuous time, one forged by America's conflict in Vietnam. 

The intro portion of Apocalypse Now, the dreamlike sequence of Captain Willard in a Saigon hotel room, complete with flame, napalm, alcohol consumption, cigarettes, guns, divorce letters from home, blood, broken mirrors, and untold torment and pain, ends with Captain Willard staring at a rotating ceiling fan while Jim Morrison overlays the already bizarre and maddened mood by stating"Lost in a Roman...wilderness of pain, and all the children are insane...waiting for the summer rain, yeah."
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Apocalypse Now begins with a an almost still-shot of the jungle.  Upon closer view it can be gleaned that the palm trees are blowing or rustling ever-so-gently.  One can hear the slightly distorted sounds of helicopter blades chopping their way through the air.  Soon they become visible, almost floating across the screen in dream-like fashion to the slowly emerging sounds of the Doors, The End.  Suddenly, without warning, the landscape is illuminated with the orange blaze of napalm exploding onto the jungle, devouring the green foliage almost on contact.  The viewer then sees the upside down image of Captain Willard, which begins moving in a clockwise motion until upright.  Are these the images that haunted the mind of Captain Willard when he went home after his first tour in Vietnam?  He later states that when he was in the jungle he couldn't wait to go home, and after he went home he couldn't wait to get back in the jungle.