Jarhead

In 1989, Anthony Swofford (Jake Gyllenhaal) is getting trained in a U.S. Marine Corps boot camp by the choleric, hard-boiled Drill Instructor Fitch (Scott MacDonald). After finishing boot camp, "Swoff" is dispatched to Camp Pendleton.

Swoff then explains how he tried to fit into civilian life. He thought about going to college but he instead joins 'shows' some highlights of his life including taking a 'dump' and 'studying' (having sexual intercourse) with his girlfriend; who later cheats on him.

Swofford finds boot camp tough as he struggles through making friends and living day to day. He then writes "fuck it" on a light billboard with large letters before the movie cuts to him sitting in the head. In the head trying to be "sick" (by drinking a whole bottle of liquid laxative), is slipped food under the door before he is approached by Staff Sergeant Sykes (Jamie Foxx), a Marine "lifer" who invites Swofford to his Scout Sniper course. After arduous training sessions that claim the life of one candidate, Swofford is one of the 8 remaining from the original 60 candidates and is selected to be trained as a sniper and paired with his roommate Troy (Peter Sarsgaard), who becomes Swofford's spotter. During all of this Swoff is put through his paces and learns a variety of sniper techniques. Although he first thinks of it as a joke, he starts to fall in love with the idea of getting to kill someone. Shortly after, Kuwait is invaded by Iraq and Swofford's unit is dispatched to the Persian Gulf as a part of Operation Desert Shield. Although the Marines are very eager to see combat action, they are forced to hydrate, wait, patrol the nearby area and adjust themselves to the arid environment. A main technique suggested for boredom and loneliness is masturbation. During the waiting period the "wall of shame" is shown and as Swoff is looking at it a fellow Marine (Fowler) teases Swoff that its only a matter of time before Swoff's girl is up there. this majorly plays on Swoff's mind throughout his deployment.

During an impromptu Christmas party thrown by Swofford, who has obtained unauthorized alcohol, Fergus (Brian Geraghty), a member of Swofford's unit, accidentally sets fire to a tent and a crate of flares. Swofford gets the blame because he was supposed to be on watch but had Fergus sit in for him. As a consequence, Swofford is demoted from Lance Corporal (E-3) to Private (E-1) and is forced to undertake the degrading task of burning "diesel fuel" (excrement). The punishments, the heat and the boredom, combined with suspicions of his girlfriend's infidelity and feelings of isolation, temporarily drive Swofford to the point of mental breakdown. He threatens and nearly shoots fellow Marine Fergus then turns the weapon on himself and demands the traumatized Fergus to shoot him. When Fergus refuses Swofford leaves the tent.

After the long stand in the desert, Operation Desert Storm, the coalition force's ground campaign, begins. The Marines are dispatched to the Saudi-Kuwaiti border. Briefly before the action begins, Swofford learns from Sykes that Troy concealed his criminal record when enlisting and will be discharged after the end of hostilities. Troy begins to keep distant from his fellow Marines. Knowing that Troy will never be allowed to re-enlist, the Marines brand him with a hot USMC iron, marking him as one of their own. Following an accidental air attack from friendly forces, the Marines advance through the desert, facing no enemies on the ground. The troops march through the Highway of Death, strewn with the burnt vehicles and charred bodies of retreating Iraqi soldiers, the aftermath of a U.S. bombing campaign. Later, the Marines suddenly catch sight of distant burning oil wells, lit only moments before by the retreating Iraqis, and they attempt to dig sleeping holes as a rain of crude oil falls from the sky. Before they can finish them, Sykes orders the squad to move to where the wind prevents the oil from raining on them.

Swofford and Troy are finally given a combat mission. Their order is to shoot two high-ranking officers in Saddam's Republican Guard, holed up at a nearby airfield. At the last second before Swofford takes the shot, a high-ranking US officer interrupts them to call in an air strike. Swofford and Troy vehemently protest but they are overruled and later watch as the planes destroy the Iraqi airfield.

On returning home the troops parade through the towns in a jovial celebration of victory. Swofford returns home to his family and girlfriend, but discovers her with a new boyfriend. Fowler is seen to be with a prostitute in a bar, Kruger (Lucas Black) in a corporate boardroom, Escobar (Laz Alonso) as a supermarket employee, Cortez (Jacob Vargas) as a father of three kids, and Sykes continuing his service as a First Sergeant in Operation Iraqi Freedom. An unspecified amount of time later Swofford learns of Troy's death (the cause of which is never specified) during a surprise visit from Fergus. He attends the funeral, meets some of his old friends, and afterwards he reminisces about the effects of the war.