"In between, I’m sitting with my folders of visual aids, images from Sudan of kids burned, people hacked up, cut-off, babies. Sometimes I would think, I can’t do this again. It was a hard movie to make, but it’s the hard ones that pay off big."

Equally important to understanding the remarkable journey Childers has made is his wife Lynn, played by Michelle Monaghan. Lynn provides Sam with the emotional ballast he needs to keep going.

"Lynn is a very strong woman," says Forster. "She is courageous on many levels and she has stuck with him even though she was left behind, not just once, but many times. There are not many women who could do that."

Monaghan counts herself fortunate to have been involved in the project. "The script was so powerful," she says. "And I just thought, this story has to be told and I really want to be a part of telling it.

"I don’t want to make movies that I don’t want to watch, and this is a movie that makes me proud."

Monaghan says screenwriter Keller perfectly captured Lynn’s voice in his script. "Jason poured his blood, sweat, and tears into this project and it shows. He had spent so much time with her so he really wrote in her voice. I felt I understood her even before I met her.

Once Monaghan did meet Lynn Childers, she learned how significant her role is in Sam Childers’ life and work. "It became very apparent to me that Lynn is a quiet giant," the actress says.

"None of this would have been possible without her. She has endured a lot and always maintained a very strong sense of family and faith. It can’t be easy to keep your family intact when your husband leaves for months at a time to risk his life in a dangerous place.

"But she gave him the strength and the confidence to pursue Angels of East Africa and she is the one who keeps the show running in the U.S."

The actress says Lynn Childers was generous and open with her as she prepared for the role. Nothing Monaghan wanted to know was off limits. "She allowed me to ask her  anything I wanted. She opened her home and her heart to me, and it was invaluable to have the freedom to pick her brain.

"I was impressed by how comfortable she is in her faith. She says all she needs is God, Paige, and Sam, in that order."

Machine Gun Preacher is out now.

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