Jack O'Connell says it was important to get all the details of Unbroken right, as the character that he plays is still alive.
O'Connell stars in the Angelina Jolie directed film, which chronicles the life of Louis Zamperini.
O'Connell takes on the role of Zamperini in the film, and says it was great have someone as experienced as Jolie alongside him.
Speaking to Collider, the actor said: "Yeah, still alive. He’s 97 and still surprisingly lucid so I can’t bank on the fact that he might not be able to gauge what’s going on because he will, he will gauge.
"So we had to have my hair looking more or less looking good, because he prioritised his image once upon a time so there was a lot of emphasis on that too.
"Luckily I had someone like Angelina around who’s kind of done it before, every adversity I was trying to face, she’s done time and time again and I certainly grew and strengthened as an actor or a human.
"I’m 23 now so I’m playing these roles where I’m portraying youngsters that are becoming adults typically, and this was a real example of that, I don’t think you’ll get a greater example of that actually."
This is the second live action feature film for Jolie, and she has brought together a great cast that includes Domhnall Gleeson, Garrett Hedlund and Jai Courtney.
As for O'Connell, it is going to be a busy year for the actor with Starred Up, '71 and 300: Rise of an Empire all set for release.
Unbroken is released 16th January 2015.
Tagged in Jack O'Connell