The movie is based on the true events and the experience of the film's writer Chris Roessner during the Iraq War.
Writer Chris Roessner said that Henry Cavill was perfect for the role because besides his respect for the military, he had the perfect look for the character. Roessner said, "He sure as hell looked the part. I mean the guy is Superman. You've seen the films. He's in ridiculous shape. And these Special Forces soldiers, when they aren't on missions they're working out. That's the lifestyle and the body type follows. So that was clear."
Glen Powell plays a loud and proud Texan soldier and was required to pack on 20 pounds in three weeks. He said that it took a suitcase full of protein powder and advice he got from Sylvester Stallone on the set of The Expendables 3 (2014): "Just get your forearms and traps to bulge and you'll look massive on camera." Powell showed off his beefed up physique in a shirtless workout scene in the film doing intense barbell deadlifts.
During the visit to the Sheikh's house, Sgt. Harper (Logan Marshall-Green) gives back the coffee cup using his left hand. Giving something to someone with your left hand is extremely frowned upon in rural Arabic culture and in reality any soldiers who would have to come into contact with locals would have been briefed on the etiquette (similar to removing your shoes indoors and certain other cultural rules).
Luke Evans was originally cast but dropped out before filming began and was replaced by Logan Marshall-Green.