"That which does not kill us makes us stronger," Friedrich Nietzsche famously wrote in "Twilight of the Idols" in 1888, 25 years before Louie Zamperini was born, but the extraordinary life of the subject of "Unbroken" is the very definition of the phrase.

As documented in Laura Hillenbrand's best-seller, "Unbroken: A World War II story of Survival. Resilience and Redemption," Zamperini was an Olympic runner turned bombardier who crash-landed in the Pacific Ocean and survived 47 days in a raft surrounded by sharks, only to suffer two years of starvation and torture in a series of Japanese prison camps. His wartime experience and the strength of spirit that enabled him to survive the ordeals comes to theaters Dec. 25 in "Unbroken," directed by Angelina Jolie and starring British actor Jack O'Connell. But it has taken 57 years to bring Zamperini's story to the screen.

In 1957, the rights to his autobiography "Devil at My Heels" were acquired by Universal with an eye toward making a movie starring Tony Curtis, but it was shelved before a script was written. Several attempts to revive the project over the years went nowhere. Meanwhile, Hillenbrand, while doing research for her book "Seabiscuit" in 2001, came across an article about Zamperini and eventually contacted him. That correspondence led to the 2010 biography that sold 4 million copies and revived Hollywood's interest in the story.

Universal optioned the book, and screenwriters Richard LaGravenese and William Nicholson wrote drafts, one of which producer Matthew Baer showed to Angelina Jolie, who had made her directorial debut with "In the Land of Blood and Honey." "I knew I wouldn't be any good at directing another film unless I was really moved by the subject matter and felt it was important," she said, realizing, "this was what I should put out into the world. We need to be inspired and reminded of the strength of the human spirit. It speaks to all of us. But I had to fight to get the job. Not only prove to the studio I could do it, but later, to prove it to myself. And I also had to prove it to Louie, which took some time."

Then there was the issue of just how much of Zamperini's life to depict in the movie. The last third of the 400-plus-page book covers his post-war life, including his struggle with alcoholism and PTSD nightmares and flashbacks, nearly losing his job and marriage, then finding his faith and forgiving his captors and devoting his life to helping others, particularly troubled youth. All that was jettisoned in the final version of the screenplay by writers Joel and Ethan Coen.

Zamperini's wartime ordeal takes center stage, with flashbacks to his hell-raising early life as a budding juvenile delinquent before his talents on the track took him to the 1936 Berlin Olympics. (The film makes no mention of him briefly meeting Hitler there or stealing a Nazi flag as a souvenir.) Of the 27,000 POWs imprisoned in Japanese camps in World War II, 40 percent died, and Zamperini was nearly one of them, suffering brutal mental and physical abuse by his captors, particularly the sadistic Mutsuhiro Watanabe, also known as "The Bird," for more than two years.

Phil and Louie are

Phil (Domhnall Gleeson, left) and Louie (Jack O'Connell) are 'rescued'  by the Japanese navy in 'Unbroken.' (Photo: Universal Pictures)

The varied terrain and climate of Australia provided the ideal location for the 14-week shoot, including the Kwajalein, Omori and Naoetsu camps that were recreated for the film. "So many documents from the war were destroyed on the Japanese side that it was not easy to research a place like Omori," says technical advisor Tomo Miyaguchi. "We had to rely on American accounts and war crimes tribunals, also books written by former POWs."

Commander John Fitzgerald, the POW played by Garrett Hedlund in the film, had documented his experiences in a diary that Hillenbrand used in her research. It filled in the blanks for a climactic incident that Zamperini could not recall in its entirety: When "The Bird" forces a weak Zamperini to hoist a heavy six-foot plank above his head — if he dropped it, he'd be shot.

It was a particularly harrowing sequence to shoot, even though Jolie had planned it thoroughly in advance. "I fainted twice, between the diet and the Australian sun. The plank won," remembers O'Connell. By that point, he had lost 26 pounds to convey Zamperini's starvation. "I had a team of professionals for the weight loss. It was a brief experience, but one that was torturous enough for me to never want to do it again. But Louie's real life dwarfed any hardship that I experienced, so I wasn't about to complain."

The Bird leans in to threaten Zamperini in 'Unbroken'

'The Bird' (Miyavi, left) leans in to threaten Zamperini (O'Connell) in a scene from the movie. (Photo: Universal Pictures)

Japanese rock star Miyavi, who makes his film debut, called the scene "torture for me too. I threw up. It was from responsibility because it's such an important scene. I had to express depression, confusion, madness and fear at the same time without dialogue. It was a big challenge, and I got to the point where I couldn't control myself. I kept crying and crying."

Before working on the movie, Miyavi had never heard of Zamperini, which is understandable because the book "Unbroken" was "not popular in Japan at all." He hesitated to tackle the role. "I didn't want to represent any negative side of Japan. I was not sure I was capable of doing this before I met Angie." The director convinced him that "it would be meaningful even as a villain to deliver the global message of forgiveness and unbroken spirit."

The raft sequences, filmed in the Pacific off the coast of Queensland and at water tanks at Warner Australia Studio on the Gold Coast, where airplane scenes were also shot, provided additional challenges. Technical adviser Bob Livingstone, an expert in WWII aircraft, met with Jolie and the cast and crew before the filming got underway. "Angie had a lot of specific, informed questions about the aircraft and the operation of a WWII bomber. It helped that she is a pilot herself with an instrument rating and immediately understood all the fine points involved," he noted.

To dress the actors in a narrative that spans two decades, costume designer Louise Frogley rented period and clothing, with input from military uniform expert Joe Hobbs. "We see Australian forces, American soldiers and flyers, Japanese military and prisoners of war," she said. "Joe was able to find so many original pieces that we used in the film. When necessary, we manufactured the military garb. But even with uniforms, we always took character into account. We also made these costumes a size too big for everyone so that the actors and extras, all of whom were terribly thin anyway, would look as if they were swimming in their clothes."

Louis Zamperini

Louie Zamperini poses in his bomber jacket before his death in July 2014. (Photo: Universal Pictures)

Jolie, who had become close to Zamperini in the course of making the film, was able to show a rough cut of "Unbroken" to him before he died of pneumonia in July at the age of 97. "I brought the film on my laptop and sat with him and had the great honor of watching this extraordinary man at the end of his life watch his life and remember who he was, what he'd done, his family. I watched his eyes as he watched the film. What a gift," she said.

While Miyavi concedes that "Unbroken" will be tough for Japanese to watch, he is confident that its message will transcend the negative aspects. "It's all about Louie's message that goes beyond boundaries and nationalities. The message is we're not going to let this happen anymore and we have to learn from that generation. They saw friends die and were separated from friends and family but they endured. It's all about how strong a human being can be."

Jolie echoes that sentiment. "There's so much pain in the world," she said. "I feel that we need stories like this today — the journey of a man finding his way through darkness and into the light — stories that can help us, inspire us, show us something remarkable and make us feel positive about life."

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