“I think there’s a lesson in this… stay true to your heart, to what you believe in.”

Peter Berg, director of both box office turkeys and triumphs, knows of what he speaks. His most recent film, ‘Lone Survivor’f has taken the number one spot in the US, pocketing over $100million. The one before that was ‘Battleship’, a strange game-meets-Aliens-meets Rihanna combo that sank to the tune of similar amounts.

“I walked onto the set of 'Battleship' every day trying as hard as I could to make an entertaining film,” he tells me now. “With mixed results. But I don’t regret it. None of us were sitting there, going, ‘Oh this is just a big joke.’ You have to approach every movie as a passion. You have to fall in love with it.”

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'Lone Survivor' stars Taylor Kitsch, Mark Wahlberg, Ben Foster and Emile Hirsch

He shifts in his chair. I feel a ‘however’ coming… and sure enough…

“I’m 50 years old, I don’t know how many movies I’ll get to make, but I intend to make films that I connect to, that I feel very passionate about. I have no interest in spending four months in front of green-screen computer-generated effects. I want to make more films like this.”

‘This’ is ‘Lone Survivor’, his big screen adaptation of the memoir of Marcus Luttrell, a Navy Seal who was sent with three other men deep beyond enemy lines in Afghanistan, where they were faced with a moral dilemma, and then had to fight their way out. Mark Wahlberg is Luttrell, with Berg’s regular (and 'Battleship' alumnus) Taylor Kitsch joining Emile Hirsch and Ben Foster. As the title might just have hinted, not everyone made it back.

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Peter Berg directs Mark Wahlberg as Marcus Luttrell

“The book really registered with me,” says Peter Berg. “I thought it was a great story and a great tale, with a moral dilemma at its core.”

With four years of work on the project, including being embedded with Navy Seals at one point, it’s inevitable Berg’s views of war and warcraft will have shifted.

“It certainly made me realise the old days of war where there’s a country against a country, Germans in one uniform, English in another, you fight until one country takes it, surrender and it’s over…those days are over,” he reflects.

“I’m a believer that sometimes it’s necessary to fight. We’re lucky to have men and women who will put themselves between evil and our lives, so we’re able to sit eating oranges in hotel rooms (which is what Peter Berg and I are currently doing).

“It’s deepened my appreciation of how tricky it all is now. If anything, my feelings are we need to be more careful when we decide to sign a declaration of war, because it’s going to mean sending men like these into danger.

“We need to have a point of view on it. If we’re supporting a war in Afghanistan, we need to support the soldiers out there, when they come home, their families… and if we don’t support it, then we need to write letters, protests, getting our voices heard because there’s a good chance something like this is going to happen.”

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Peter Berg (left) with Mark Wahlberg and Marcus Luttrell

Despite its box office clout, there has been some criticism of the acute violence depicted in some of the combat scenes. Peter Berg is unapologetic.

“You see Mad Axelman get shot in the face,” he says. “Well, I’m sorry but that’s what happened. I know many people would rather read Vogue or the Tatler, because it’s easier to look at, but that doesn’t mean we don’t need to understand what’s happening.

“What bugs me is people who read, ‘Oh, four people got killed in Afghanistan, oh Lindsay Lohan’s on her third rehab, but she’s doing a lot better…’ with equal weight on both stories.

“The media’s culpable, but we’re as culpable as consumers. We need to figure out a way of making our public more aware and more accountable so they’re not sitting around, idly ignoring the fact that we’re at war, reading about Lindsay Lohan and One Direction with the same voracity as they do about our soldiers. We need to remind people that this is real.”

'Lone Survivor' is in UK cinemas now. Watch the trailer below...