Jake Gyllenhaal's audition scene was the one where he points a rifle straight into the face of one of his comrades and has a mini-breakdown. When filming this actual scene, Gyllenhaal actually knocked out one of his own teeth when he turns the gun on himself, not to mention hugely upsetting his co-star Brian Geraghty who felt that Gyllenhaal had effectively brutalized him. This led to the later scene in the film where Swofford apologizes to Geraghty's character, a scene that wasn't in the original screenplay. The scene helped smooth over the tense relations between the two actors.
When Swofford is ordered to clean the latrines, one of the receptacles has the words "Abandon all hope, ye who enter here." This is a famous line from 14th century poet Dante Alighieri's "Inferno", and is the inscription above the gate of Hell as the poet walks through it. The symbolism is that whoever is cleaning the latrine is going through "hell", as it was one of the worst duties for a soldier to have to do.
At the time of filming, Peter Sarsgaard was not yet Jake Gyllenhaal's brother-in-law. Sarsgaard first started dating Jake's sister, Maggie Gyllenhaal, in 2002. The couple got engaged in 2006, the same year they had a daughter and were finally married in 2009.
Jake Gyllenhaal was convinced he had blown his audition, especially after several months had passed and he hadn't heard back from Sam Mendes. An impassioned message left on Mendes's voicemail swung the decision in his favor.
Filmed in the Imperial Valley in Southern California, which features conditions very similar to Iraq. Marines did use one of the local towns, Brawley, for training purposes due to similarities to Iraq.
Sam Rockwell had one scene ("Payback") playing Swoff's uncle Walt, a Marine who served in the Vietnam war and who encourages the young Swoff to join the force but that scene was deleted from the film. It can be found on the DVD and some online sources.
Staff Sgt. Sykes, played by Jamie Foxx, originally had a tattoo of a panther on the back of his shaved head. Foxx sported it during his award sweeps for Ray (2004). The tattoo was eventually digitally removed in post-production by director Sam Mendes, because he felt it made the character too "hard core."
The PB pills the Marines are issued are pyridostigmine bromide pills. They were designed to increase the effects of the atropine and oxime postexposure antidote that is self-administered to reduce the chances of dying from nerve agents such as soman.
The desert locations were scouted in the summer months. When filming actually began, it was in the winter after rain, so vegetation had sprung up on what was supposed to be barren land. All of this had to be removed, often digitally.
According to Iván Fenyö, almost 70% of his performance was cut out. Two months before the release of the movie the director phoned Ivan and told him that the studio didn't wanted most of the lines he had in the movie. According to the actor, some of his parts was about his notices as an East-European about democracy and the Gulf War.
Iván Fenyö, a Hungarian actor who plays an insignificant side role in this movie is sending an easter egg message to his compatriots. In the scene when the Marines are setting up their tent, he's seen in the background applying a Hungarian national flag as a decoration.