It has taken 58 years and countless false starts to bring Louis Zamperini's story to the screen, and as I await my audience with Her Jolieness, Angelina, on the Gold Coast set of Unbroken, it feels as if it's been almost as difficult to arrange this interview. But after months of negotiations, last-minute changes of flight and location, and the threat, just an hour ago, that the whole thing might yet be called off, here I am finally, basking in her presence.

She is tiny – not short, but very slender – with olive skin and next to no make-up, wearing cotton military-style pants and thongs and a sloppy black T-shirt that slides off one shoulder to reveal a tattoo in Khmer script on her back.

I mention the physical appearance first because that's what everyone asks. What does she look like? The answer: pretty good, actually. Duh!

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She's slugging water from a bottle, telling me how she came to be directing a film about the life of Zamperini, a former US Olympian, WWII bombardier and POW brutalised at the hands of the Japanese. All the while, she has one ear open to the needs of her crew, who buzz around her and universally refer to her as "Ange" or "Angie".

"We're shooting the scene where the guys kill and eat an albatross today," she says as we gaze out over the massive water tank surrounded by blue screen that will, with the aid of CGI, come to represent the vast expanse of Pacific Ocean on which Louis floated for 47 days after his plane was shot down in 1943.

"I just keep staring at the ocean thinking, 'I don't think I would have made it'. I wouldn't have made it to 10 days, let alone more than 40."

We huddle out of the sun, beneath a canvas shelter, where she talks me through a stack of large colour photographs depicting various scenes – California, Hawaii, prison camps in Japan – all of them shot in Australia. She is funny, gracious, and not especially guarded despite the publicists' edict that there be no questions about husband Brad Pitt, breast cancer or, broadly speaking, anything personal.

Which brings us to the other question everyone asks. What is she like?

The answer: pretty nice, actually.

Unbroken is only her second film as director, and with a budget of $65 million, hundreds of extras, far-flung locations, lots of special effects and some big action sequences (including a thoroughly convincing plane crash), it's a big step up from her first, 2011's Bosnian war drama In The Land of Blood and Honey.

Film school is presumably off the cards, so how do you learn to direct when you're Angelina Jolie?

"I've asked a lot of very smart people a lot of questions," she says. "Really, you surround yourself with the best people and you don't presume to know anything, and they help you out."

According to producer Matt Baer, who had been trying to get Zamperini's story made into a film since 1998, Unbroken would never have happened without Jolie.

"For me, it was a miracle," he says of the day in November 2012 when she signed on to direct. "I finally had somebody who really had the juice [to get it made], and the power to say, 'This is one of the greatest stories that's never been told'."

But Jolie insists the project didn't simply land in her lap. "I fought for it," she says. "They were speaking to me about other, much smaller, films. I certainly wasn't being offered anything even remotely close to this and I wouldn't have put myself up for anything of this size at all."

What changed that was reading Laura Hillenbrand's 2010 book of the same name, which recounts Zamperini's remarkable story from his misspent youth as the son of Italian immigrants in 1920s California to his feats as a middle-distance runner at the Berlin Olympics, his wartime experiences, his post-war trauma, his born-again Christianity (he was converted by Billy Graham in a tent) and his ultimate forgiveness, in post-war Japan, of the soldier who had brutally tormented him for two years in two different camps.

Once she read the book, she says, "I fought for it for months with [story]boards and pitches and meetings and phone calls, and just kept working on it and trying to do all I could to show them how I saw it and how I thought it could be accomplished. But it took a very long time and I had many sleepless nights not knowing if I'd get the job – and then when I got the job I had to wait months to get the green light."

It was always possible the project could have fallen over – the first attempt to film Zamperini's story was in 1956, with Tony Curtis in the role in a film to be called The Devil at my Heels (after Zamperini's memoir). "I think it's fair to say that would have been a very different film," says Baer. "But Curtis got Spartacus instead and so it was never made."

There had been multiple other screenplays and near-misses over the years, and even when Jolie came on board it was on the understanding that the script would be rewritten again – which it was, by filmmakers and sometime screenwriters for hire Joel and Ethan Coen. 

Though it is a war movie, with plenty of action and brutality, what appealed to Jolie was the story of survival at its core.

"It sounds extremely grand, but it really is 'Man and how he evolves'," she says of Louis' journey. "It's not that he's necessarily stronger, it's not that he's necessarily smarter, it's not that he's necessarily better-looking. It's just that he's going to try again and again and again, he's going to get up again and again and again. It's a resilience and it's a strength of will that's so inspiring, it's something that people can strive for. We've all got some of that in us and it's a really nice thing to be reminded of."

Playing Zamperini is English actor Jack O'Connell, perhaps best known as the loudmouth larrikin Cook on the  British TV series Skins. Like most of the cast, he is relatively unknown – and young. One of the indelible impressions the film leaves on you is that the men who fought, and still fight, wars are generally not much more than kids.

For O'Connell, it was a transformative experience. "I feel maturer since starting," he says in a break from shooting the albatross-eating scene. "Personally, it's done me a lot of good. I feel like I'm a more patient, measured individual … I'm really glad to have an awareness of this geezer's life at the age of 23. I'd be very stupid if I didn't take on a couple of his values and try to incorporate them into my own set-up, you know."

O'Connell is covered in latex sun blisters, his skin a blotchy red. He and American actor Finn Wittrock and Irish actor Domhnall Gleeson (best known as Bill Weasley in the last two Harry Potter films) are filming their final scenes on the life raft, which are actually the earliest in the story's chronology.

"From the time the actors got the roles they had to start going on diets to lose the weight," Baer says. "We began the film with them at their thinnest; this is them in their healthy stage."

At their worst point in the finished film, the actors are just skin and bone. "It's one thing if you're on a diet, it's another if you're working in a very physical film, on a raft, in a POW camp," Baer says. "There was a need for them to be sharp and focused, but when you're starving …"

Jolie says they deliberately got the worst scenes out of the way first. "It was nice to be able to have them look forward to pizza and to be able to come back [after a break for Christmas] and be able to laugh and have fun, because the beginning was really hard," she says. "They were tired and skinny and hot and their energy was low. There was a lot of the abusive scenes and the heavy scenes and the pain. It's been tough."

Her actors say she exudes empathy as a director. "She's incredibly supportive," Gleeson says.

But, he adds, she can also be firm. "There's no doubt about who the general is, you know. She's in charge; it's her movie."

When I talk with Jolie a second time, the day after the world premiere of Unbroken in Sydney in November, I ask her if there are times when she has to play tyrant.

"Oh sure," she says. "And that's what you want from a director. There are days when you think, 'You may hate me, but when you see the final film it will have been worth it'.

"My job is to make the film great, not to make friends with everybody – even though I did make friends with everybody. When we were doing scenes of Jack racing, the mother in me, and the friend in me, sees his legs cramping up, sees him exhausted, and wants to just call it a day. And then the director in me wants five more takes." It's a form of tough love, she says. "But you know, in the end he's going to see the scene and he's going to be proud of his work, and that's the best way to take care of an actor."

For her own part, Jolie says she's ready to slip away from acting, ready to turn her attention full-time to directing. And since Unbroken, she has already finished shooting another film – a dark marital drama called By the Sea, which she wrote and in which she stars with Pitt – with another one in the works.

"I love directing, I'm much happier directing," she says. "I like spending two years on something and learning about it and being able to tell stories like Unbroken. And I like being pushed mentally to have to learn so much and be a part of every single aspect of a production."

She likes actors, she says, and the process of acting, but "I actually prefer it when it's not me. I like to watch people give performances and help them with their emotions and get through it … I'm very interested in that but I'm very happy to do it with others."

Long before anyone had seen a single frame of Unbroken, it was attracting Oscar buzz. Now the first reviews from the US have emerged, and the response has been muted. It's an efficiently made film, the critics have said, and faithful to the story, but it's also missing a little something. Louis can run and he can take a hell of a beating, but beyond that …?

But if Unbroken plays a little like The Passion of the Christ in khakis – he suffers; he clings to his faith; he suffers some more – Jolie knows she won the approval of the one viewer who mattered most.

She didn't know Louis Zamperini before she became involved in the project, but they became friends. In fact, she soon discovered he lived in a house just a couple of hundred metres from her own.

"From my bedroom window I can actually look out and see the corner of his house," she said on the Gold Coast set in January. "The number of times he was sitting in his house wondering if anybody was going to figure out this film, and the number of times I sat on my bed thinking, 'There's got to be something where I can be of use, something good I can do that's inspiring'. And we must have both had that for years, and if somebody had just screamed out the window we'd have figured it all out."

Zamperini was still alive then; in July, he died, aged 97.

At the premiere last month Jolie was still tearing up at the thought that he had not been there to share the moment. He had at least seen the film; she showed him a rough cut on her laptop computer.

"You think you're the director bringing the movie to the subject and you want to know their opinion," she says of that intimate screening. "And then you realise, no, you're in fact with a man who is at the end of a very extraordinary life, who is watching his life before his eyes, and remembering his friends who died.

"It was a very different experience," she says. "It had nothing to do with being a filmmaker, and was more about being a human being."

She pauses here, once again tearing up.

"It was going into his memory and bringing him to these places," she says. "Which is all I could have asked for."

Unbroken opens in Australia on January 15.

On twitter: @karlkwin