Angelina Jolie never expected to direct a film with shark attacks, plane crashes and prisoner-of-war camps, but she found the story of a World War Two hero so compelling she tackled them in "Unbroken," a biopic
about survival, faith and forgiveness.

The Oscar-winning actress and second-time director was half-way through Laura Hillenbrand's best-selling book about Olympic runner and POW survivor Louis "Louie" Zamperini when she knew she wanted to make it into a film.

"I would never have thought of myself handling that kind of cinematic filmmaking," said Jolie, 39. "But I cared about the story so I had to suddenly learn to do all those things." The film opens in US theatres on Christmas.

Shot in Australia with a script by Joel and Ethan Coen, "Unbroken" follows Zamperini as a bombardier in an air fight with enemy planes and through two harrowing crashes. After his plane plummets into the Pacific in 1943, he survives 47 days adrift in a life raft battling starvation and sharks. He is fished out of the ocean, imprisoned in Japanese POW camps and tortured, pushed to the edge of human endurance.

"It's a movie for everybody," said Jolie. "I want my children to know about men like Louie, so when they feel bad about themselves and they think all is lost, they know they've got something inside them, because that is what this story speaks to, what is in all of us."

English actor Jack O'Connell, 24, won the National Board of Review's 2014 breakthrough performance award and plaudits for his portrayal of Zamperini.

O'Connell met Zamperini before the former POW died in July at the age of 97 after finding faith and forgiving his tormentors. The actor described the two meetings as awe-inspiring experiences. "I shook his hand before I left for Australia and said to him, 'You're in good hands, mate.' I promised him that much and he said he knew. I had to keep honouring that promise," the actor said.

O'Connell had a small taste of what Zamperini endured during a prison camp scene when he was forced to hold a large, heavy wooden plank high over his head. The actor fainted, twice.

"Louie's ambition was for people to feel a sense of empowerment in themselves by his account," O'Connell said. "That's been the case for me. He certainly took me to extremes that I thought I wasn't capable of."