The film was shot in Fort Hood, a sprawling military base in Texas.
"I was literally standing in a field holding this woman, who I'd never met before, in the same field where she watched her husband deploy and saw him for the last time. She was sobbing."
Clearly, this is an emotional subject for Bosworth. "I read the book. I think Martha very accurately and in a revelatory way was able to describe the experiences of these men and women on the frontlines away at war, as well as on the frontlines at home."
Not totally unfamiliar with the subject matter, she adds, "My grandfather was in the military. He actually was in numerous wars, so I know a little about it.
"We live in a country where we are protected by these men and women, so this was a project that was particularly important for me because it felt in a very truthful way what they experience and the sacrifice that they make for us, for our safety. It felt like it was an important story to tell so that we can understand the depth of what they do and have gratitude for their services."
Bosworth made her film debut at age 15 in The Horse Whisperer. Four years later, she landed the lead role as a teenage surfer in Blue Crush and went on to star in such indie fare as Wonderland (2003), By the Sea (2004), Straw Dogs (2011), and Still Alive (2014).
Bosworth was named Katherine "because it means strong willed and determined".
"When I was born, the doctor said I came out so aggressively and determinedly that they thought I was a boy.
"I've always felt very strongly about standing up for what I believe in. I'm an only child, so I've always felt quite independent. Even when I was at school, from the age of 5, I would stand up to bullying and was enraged by that behaviour."
Now that she's in the schoolyard of Hollywood, where predatory bullies prey on the young and naive, does she stand up for the victims of sexual misconduct?
"I set you up for that segue!" she says, laughing. Bosworth starred in the Weinstein-produced SS-GB TV series earlier this year.
"I often get asked whether I had an experience with Harvey Weinstein that was inappropriate. I did not." She pauses. "One of the things that I want to say, which is very important, is that I was asked to have a meeting with him when I was very young. My manager at the time was a woman named J.J. Harris [who has since died].
"When I was asked to have a breakfast at the Peninsula Hotel, she offered to be my chaperone. She didn't warn me [about him]. She just said, 'I'm there with you.' It moves me now to think about it because she put herself out there in a way that I think is really important. "This idea of acceptable sexism in this industry has been a problem for years, and, I think, across the board. We've had enough. I mean that for both women and men, my husband being one of them. He's had enough. He pledges to not accept this any longer and I do too."
Bosworth has been married to director Michael Polish since 2013. She was formerly romantically linked to Orlando Bloom from 2003 to 2006 and Alexander Skarsgard for two years, ending in 2011.
The couple worked together on the films Big Sur (2013) and more recently, this year's Nona, about sex trafficking in Central America. "We have a creative love-fest between us," she says.
"We hope to have babies one day but in the meantime, we joke that we're constantly having babies with the movies we work on together. There's a lot of laughter between us and I love working with him." She grins. "He's brilliant."
When they're not working, they enjoy every minute together. "We have a property in Montana where we really love to spend time. I'm an avid reader and he loves to draw. He went to Cal Arts [university] as an artist, so his favorite gift was the iPad with the pen. He'll just he'll sit there and draw for hours and hours and I'll sit there and just read book, after book, after book. Time off for us means still being creative, just in a different way."
Lowdown
The Long Road Home, National Geographic, Tuesdays 8.30pm
