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.
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.
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.