Taking a few obvious cues from Full Metal Jacket, Jarhead opts to focus its first act on military training. The influence of Kubrick's film is obvious in the rough training process that is depicted. Even the initial interactions between Swafford (Jake Gyllenhaal) and his Drill Sergeant are somewhat reminiscent of Gomer Pyle and Gunnery Sgt. Hartman. Jarhead even lifts the "this is my rifle" speech from Full Metal Jacket and also includes a scene where the same speech is shouted by an obviously unstable marine. Similar to Kubrick's film, Jarhead also explores the theme of how people are changed by war, if for different reasons.
When the audience first meets Anthony Swofford, he appears to be more or less an ordinary person. While the film never states his precise reason for joining the marines, it does allow a brief glimpse into his background. It is shown that he was conceived during the war in Vietnam, and there appear to be several personal moments that Swofford tries to keep the audience from seeing (represented by a door closing on the camera). He also shows some of his happier memories, which include his girlfriend Kristina (Brianne Davis). Swofford even admits in his narration that he thought joining the marines was a bad decision, and with the training he goes through it is not hard to see why.
However, he is changed very much as a character once he goes through training. On his first day he is attacked by several marines, tied to his bed, and seemingly branded with a "USMC" logo. This later turns out to have been nothing more than a sick joke meant to scare new recruits, but the fact that people would find humour in such an activity already shows just how much their time in the military has affected their minds. Swofford himself is broken and humiliated during this time, and, much like Private Pyle, he is turned into a killer by the time he is finished.
Throughout these first twenty minutes, the instructors spend time talking about combat conditions, trying to simulate the experiences of being under enemy fire (an exercise which results in the accidental death of a recruit). They are creating expectations for Swofford and his fellow soldiers towards what they will face in an actual combat zone. They are obviously conditioning the marines to get a thrill out of combat, and to be prepared to kill. By the time they have finished their training, they are eager for a chance to use their skills on the battlefield.
This is emphasized when the marines are shown at a screening of Apocalypse Now, during which they cheer upon seeing the famous "Ride of the Valkyries" sequence. They are obviously thrilled to watch Lt. Colonel Kilgore's air cavalry massacre a Viet Cong outpost. Evidently, none of them have ever seen the rest of Apocalypse Now, which focuses in large part on the insanity of war (maybe some of them walked in late and missed the opening scene where the main character was obviously suffering from post-traumatic stress disorder).
It is, however, also possible that they just don't care about what Apocalypse Now is actually trying to say. By now the only thing they seem to understand is killing, and seeing it on a large scale gives them an adrenaline rush. This interpretation would also be supported by the strange excitement they display upon being told that the Gulf War is happening. Immediately they begin cheering as they eagerly leave the theatre for their deployment. They are all expecting action and waiting to get their first kill.
Of course, as soon as the marines are on their way, it soon becomes clear that things are not as clear cut as they appear. On the plane, it is revealed the soldiers are hardly noble individuals. One man admits that he only joined the marines to get out of jail time. Several of the marines are also shown to be perverts, even sexually harassing the flight attendants, who prove to be experienced in warding off their advances. Upon arrival, they soon find themselves being briefed about the current political tensions with Saddam Hussein, during which they are quickly rallied into an enthusiastic mob shouting their desires to kill "Iraqis."
The Swafford seen in the film's opening might have had trouble facing this, but now he is cheering alongside them. Of course, the soldiers appear to be more interested in the adrenaline rush of combat and a possible chance at killing than in any actual service to America. Shortly after their arrival in the Middle East, Swafford is seen in a conversation with several other soldiers during which the politics of the Gulf War are referenced. One of the soldiers points out that America was responsible for putting Saddam in charge and is only acting now because that has backfired on them. Another responds that they should simply ignore the politics and focus on following orders.
This is where Jarhead reveals a very different theme from most war films. There is very little action to be found, largely because this is a new type of warfare. Unlike previous conflicts such as World War I, World War II, and Vietnam, there are no clearly defined "front lines" and one cannot always be sure of where and when they will encounter the enemy. It is hard even to find the enemy at all. Since the Gulf War, this has been the template of modern combat, with similar conflicts emerging in Iraq and Afghanistan. This means revealing another side to war, which is the waiting. The long and tedious periods in between combat situations prove to change the characters far more than any actual combat.
With a bunch of men grouped together in a small camp waiting for a chance to take another human being's life, it is not hard to imagine that they would get restless. Swafford and his partners have to spend months at this one camp, and he is constantly promised that he will soon get his chance, though it never seems to come. It is obvious that this has a major effect on Swafford's mind, as he begins to grow increasingly restless, agitated, and reckless. Many of the soldiers do, and this leads them to try out strange activities to occupy themselves such as placing bets on scorpion fights. This detail is not helped by drills conducted by Staff Sergeant Sykes (Jamie Foxx), which include forcing the men to wear gas masks that appear to be very hot.
On top of all this, there is the pressures of maintaining a positive image in the media. When a news crew arrives, Sykes is quick to enforce rules about what the marines can say, and when it is pointed out that this obviously infringes on their freedom of speech, he retorts by claiming they have no rights. That doesn't stop some of the marines from trying to sneak in remarks about how they are actually feeling. At one point, Swofford can be seen throwing a football around in a manner reminiscent of The Great Escape, when the marines are suddenly forced to play while wearing their gas masks.
As the film goes on, the marines become increasingly desperate. The Christmas party includes a literal gasoline-drinking contest, as well as multiple accidental fires, and eventually Swafford ends up pointing his own gun at the head of Private First class Fergus O'Donnell (before turning the gun on himself and trying unsuccessfully to get O'Donnell to pull the trigger). By the time Swafford finally finds himself anywhere near actual combat, he barely seems phased by it. He is surrounded by enemy fire and explosions, yet continues to sit in the same position, hardly noticing even while his comrades desperately try to persuade him to take cover.
Swofford and his spotter Alan Troy (Peter Sarsgaard) eventually given a sniping mission. They are tasked with shooting two officers to assist a combat mission, but even this is not as simple as they would like it to be given that he has to get official clearance before pulling the trigger. The stage of setting up goes perfectly, except when given permission, Swofford hesitates to take the shot. This is an important detail, as this is in fact the first time he would be in any position to kill someone. Up until this point, he has only fired a gun in target practice, but now he is faced with killing another human being. This is a common problem faced by soldiers, where even the uncontrollable urge to kill makes it hard to pull the trigger.
After the air strike, Swofford and Troy leave their sniping position and after briefly running through the desert are shocked by what they think is a massacre of American soldiers. It actually turns out to be a party celebrating the end of the war. One would think that a person would be fortunate to have ended up in Swafford's position. He has literally gone through the entire war without taking a single life, something most soldiers are unable to do. However, it is hardly a satisfying moment for him. All he can do is note that he never got a chance to fire his rifle, and shoot is into the air at a non-existent target.
The ending of the film shows another aspect of war, one which has only recently started to come into public recognition. This is the psychological impact the war has on soldiers. PTSD has been around for centuries, and was first given the name "Shell Shock" during World War I, but at the time it was dismissed as nothing more than a sign of cowardice. Cases of PTSD would continue through World War II, Korea, Vietnam, and even Iraq and Afghanistan, but it was not until recently that it became recognized as a serious psychological condition that required careful treatment. Jarhead takes the time to show that in its final moments.
Swofford manages to return home, as do many of the other soldiers who served with him, but the fact remains that they have been changed. They continue to be haunted by memories of their experiences in the marines, and in that sense they can never truly leave the war behind them. These feelings are often experienced by returning soldiers, many of whom have difficulty adjusting to civilian life. Swafford explains this in his final voice-over monologue, and it is also visually conveyed through the final shot.
Jarhead ends with Swofford approaching a window in his house overlooking a city. The camera tracks past him, and as it moves to his other side, the city transforms into a shot of the desert. The end result is that no matter what he does, Swafford can never truly escape his past. He will always remember being in the marines, the adrenaline rushes he experienced and his uncontrollable desire to kill. These memories will continue to affect him, just as they have to those who served in World War I, World War II, and Vietnam.