Angelina Jolie says she took on the challenge of filming "Unbroken," which has defeated many before her, because she wanted to create a story of hope.

The second-time director is in Berlin promoting the new film, the survival story of Olympic and World War II hero Louis Zamperini.

"I wanted to learn from Louis and be around this great man, but I wanted to put something out in the world that reminded us all of the strength of the human spirit and brotherhood and faith and all of the things that will, in the end, get us through these dark times," Jolie said.

Universal Studios purchased the rights to Laura Hillenbrand's book "Unbroken: A World War II Story of Survival, Resilience, and Redemption" in 2011, but it took the involvement of Jolie and screenwriters Joel and Ethan Coen to finally bring it to the big screen.

"The fundamental turn in it becoming a movie was when Angelina came on," said producer Matt Baer at a news conference Tuesday. "She had the solutions to what had ailed the script prior, which was being able to figure out structurally along with the Coen brothers how to craft a movie that played with time and still maintained the essence of the character."

"Unbroken" was mostly shot in the Australian state of New South Wales and premiered in Sydney on Monday. It's scheduled to be released in the U.S. on Christmas Day.

British-born actor Jack O'Connell stars as Zamperini, who survived 47 days drifting in a life-raft at sea and was later a Japanese prisoner-of-war.

As part of the audition, O'Connell was locked in a dark cell and beaten with a rubber baton - but that was only the beginning of the difficulties he faced in the lead role.

"The biggest challenge of my life yeah, easily. It all accumulates to one pretty enormous test for me as an actor. But the whole time I had Louis' example constantly dwarfing whatever hardship I was experiencing. So once you accept the reality there, it would be very inconsistent of me to start feeling sorry for myself then."