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The film deviates from Marcus Luttrell's account of the decision to release the goatherders. In his book of the same name, Luttrell describes Lieutenant Murphy favoring release of the prisoners, but placing the decision up to a vote, with Murphy and himself favoring release, Axelson in favor of killing the prisoners, and Dietz abstaining. Luttrell's account was controversial, as military procedure requires the officer in charge to give legal orders, and Murphy's father objected to the notion that his son would abdicate his responsibility. In the film, the mens' respective opinions are reflected according to Luttrell's version of events, but Murphy is depicted as decidedly telling the others "This is not a vote" before giving the order to release the prisoners.
The tumbling and falling scenes were filmed on-location without CGI enhancement, and necessitated that the stunt performers subject themselves to genuinely hard falls. After one such stunt, Mark Wahlberg's stunt double had to be hospitalized.
In real-life, the firefight Marcus Luttrell and his sqaudmates engaged in, with the Taliban, lasted far longer than in the film, and the whole ordeal was five days, compared to the three depicted in the film.
Actual military veterans were used in the film to fulfill extra and acting roles.
Mark Wahlberg claimed that the real Marcus Luttrell was initially very guarded with him when they first met, and would not make eye-contact during conversation. Wahlberg earned his trust over the course of a few weeks, before Luttrell was willing to speak candidly.