When Iraq War Veteran and Pat Tillman military scholar Chris Roessner sat down to write his debut screenplay "Sand Castle," he wanted it to be personal and to reflect the just over 12 months he spent in Iraq.

Most movies about war are mission oriented, about taking a hill, or a village, or capturing enemy troops. Roessner's movie is also mission oriented, but it’s a different kind of mission.

"I wanted to talk about what it feels like to be a young man or woman at war and what it feels like to need the local population [to work with you] to be successful," he told Fox News.

Set in the early days of the second Gulf War, "Sand Castle" is the story of inexperienced Private Matt Ocre (Nicholas Hoult), whose unit is ordered to the outskirts of Baqubah to repair a water pumping station damaged by U.S. bombs. But as Ocre quickly discovers, winning over the locals is a job fraught with danger and extreme frustration.

Ocre's war experience, very much like Roessner's, is dependent upon his ability to work with the Iraqi people, and he soon finds out that if the locals were willing to help, they paid a high price for that.

"Not by us, but by insurgents," Roessner explained. "They were killed for helping us and they were well aware of that. That’s not something that we realized right away. We learned it quickly, but the price that people paid for helping us was very, very high."

Even though "Sand Castle" filmed in Jordan, not Iraq, it was still emotionally battering for Roessner to revisit certain aspects of his time in the war zone, especially scenes where they were filming the deaths of men who had been his friends.

"I was surprised to find that, even though I’d lived with the script for seven years, watching it happen, I really wanted to change it," Roessner said. "I really wanted to make it happen differently, and that feeling was surprising and overwhelming. But ultimately, if I changed it, I think I would do a disservice to the folks that I’ve served alongside. It was much too important for me that I stay true to those moments, but it was very, very hard."

Another way Roessner, who knew he wanted to be a filmmaker before he joined the military but couldn't afford the tuition, stayed true to his experience was by referencing a journal he kept during his tour in Iraq.

"I came back from Iraq when I was 20 and I said, 'What’s fascinating about war is that if you’re a 19-year-old kid from Arkansas with a GED, war will turn you into a philosopher,' and that is absolutely true."

An example of a scene reconstructed from his journal is a conversation in which one of the men in his unit tells Ocre that "there's a bullet out there for everyone."

"It is something that was discussed but it doesn’t mean we talked like that all the time -- absolutely not," Roessner recalled. "And indeed, they don’t talk like that in the film the entire time, but my journal is filled with little bits of dialogue of things that people would say to me. They weren’t intending to be philosophical at times. But I got the wisdom. It never left me, obviously, because it made it to the film a decade later. You’d be surprised at how intelligent people get when the bullet starts flying."

"Sand Castle," also starring Henry Cavill, Glen Powell, Logan Marshall-Green, Neil Brown Jr., and Beau Knapp, premieres on Netflix on April 21.