Apocalypse Now

In 1969, during the Vietnam War, United States Army Special Forces Colonel Kurtz has gone insane and now commands his own Montagnard troops, inside neutral Cambodia, as a demi-god. Colonel Lucas and General Corman, increasingly concerned with Kurtz's vigilante operations, assign MACV-SOG Captain Benjamin L. Willard to "terminate" Kurtz "with extreme prejudice".

Willard, initially ambivalent, joins a United States Navy river patrol boat (PBR) commanded by Chief, with crewmen Lance, "Chef", and "(Mr.) Clean" to head upriver. They rendezvous with surfing enthusiast Lieutenant Colonel Bill Kilgore, 1st Cavalry commander, to discuss going up the Nùng. Kilgore scoffs, but befriends Lance after discovering his surfing experience and agrees to escort them through the Nùng's Viet Cong–held coastal mouth. They successfully raid at dawn, with Kilgore ordering a napalm sortie on the local cadres. Willard gathers his men to the PBR and journeys upriver. Read more on Wikipedia.