Matt Damon was grateful when actual U.S. soldiers were cast alongside him in GREEN ZONE - because they were able to share their own war experiences to ensure his portrayal was authentic.
The actor plays an army officer searching for weapons of mass destruction in Iraq in the new thriller, which features dozens of real military members.
Damon admits it was a challenge to play their leader, but was relieved to have their input.
He tells Britain's Live From Studio Five, "A big part of the role for me was getting comfortable enough to give these guys orders because I did not feel that I was qualified to do that!
"As an actor you're always just trying to be believable - that's really my only job. If at any point you don't believe what I'm doing or I am who I say I am, then I've failed. As a result you end up seeing actors spend a lot of time close to their technical advisors, the experts who are on the set to help.
"So having 30 guys who just got back from Iraq made it really easy to fall into this (role) but also they helped me and pointed things out to me...
"To their credit, they bought into the whole world that we were creating. They wanted the film to be good and they wanted my portrayal to feel authentic, so they realised really quickly that their help was a welcome thing."