Moviegoers will get to know more about Louis Zamperini and his incredible story through Angelina Jolie's directorial film Unbroken, but they will know the inspiring World War II hero better by also seeing the Billy Graham Evangelistic Association's new documentary about him.

The association announced last week that it would release the short film, entitled Louis Zamperini: Captured By Grace, on December 25, the same day that Unbroken hits theatres.

Franklin Graham, Billy Graham's son, told Fox News Channel's America's Newsroom that though Unbroken is an excellent adaptation of the Laura Hillenbrand's book on Zamperini, the film has skipped essential parts in the former prisoner of war's story, particularly concerning his Christian faith.

"Ms Jolie's movie covered just 33 out of 39 of the book's chapters and only mentioned in passing Mr Zamperini's pivotal 1949 conversion to Jesus Christ," Graham said.

According to Graham, those final chapters are the most important part of Hillenbrand's work "since they explain how Mr Zamperini really became 'unbroken'."

Zamperini turned his life around after he surrendered himself and struggles with revenge, nightmares, alcoholism and a failing marriage to Jesus Christ at a Billy Graham Crusade revival.

"His life was transformed instantly that day, and it stayed with him the rest of his life. He never turned from what he had put his faith and trust in, and that was Jesus Christ," Graham said.

The documentary features Zamperini speaking openly about his Christian faith.

Talking about his experience in the 1949 Graham Crusade, held in a constructed tent in Los Angeles, Zamperini said, "I started to leave the tent meeting, and I felt [awfully] guilty about my life.

"Yes, I had a lot of great times, a lot of great experience, a lot of escape from death, but I still didn't like my life after the war. I came home alive. God kept His promise. I didn't keep mine, and so I went forward and accepted Christ."

Zamperini was a former Olympian distance runner who spent 47 days on a raft in the Pacific Ocean before being captured and tortured by the Japanese. His gripping life story told in the best-selling book Unbroken: A World War II Story of Survival, Resilience, and Redemption moved Jolie so much that it drove the actress to make a film about his journey.

Louis Zamperini: Captured by Grace will be made available both online and on DVD, according to the Billy Graham organisation.