Warning: Wikipedia contains spoilers
Split into two halves, the first part of the movie follows the basic training of a group of Marine recruits during the Vietnam War era under the brutal command of drill instructor Gunnery Sergeant Hartman (played by R. Lee Ermey). The drill, designed to wash away the recruits' personalities and turn them into killers, works on all of them except one: Leonard 'Gomer Pyle' Lawrence, played by Vincent D'Onofrio. After finishing the training, Lawrence kills the drill instructor and then himself, using a rifle loaded with full metal jacket ammunition, from which the movie's title is derived.
The second part then takes place in Vietnam and follows one of the recruits, "Stars and Stripes" war correspondent Sergeant J.T. 'Joker' Davis (played by Matthew Modine), as he covers the Tet Offensive. The 'Joker' soon becomes familiar with both the horror and the absurdity of war, and his moral ambiguity is one of the more intriguing aspects of the story. He and his soldiers wrap up the movie with a moving and profoundly and intentionally ironic rendition of the theme song to the Mickey Mouse Club.
Full Metal Jacket has been widely praised for accurately evoking the mood of the Vietnam War from the soldier's point of view. Recurring themes are the contradictions of war, a constant feeling of being out of one's depth, and the idea of combat in Vietnam being part of a different world, with its own rules and customs. The miasma of confusion and angst of the new world begins in boot camp, and spirals down into bloodshed before even landing in Vietnam.
In the aftermath of this film a series of policy changes came about in what was considered acceptable behavior by a drill instructor in the United States Armed Forces. All references to a recruit's family are absolutely forbidden, as is striking a recruit.
The movie was shot mainly on the Isle of Dogs, a peninsula in east London. While this was reasonable for the urban nature of the Tet offensive, it was actually used because of Kubrick's aversion to travel, especially by plane: after receiving death threats during the filming of Barry Lyndon in Ireland, he had decided never again to leave Great Britain.