The actor said that the research he did in preparation for the film was more gut-wrenching than anything that happened on screen.
Efron told Celebuzz: "The first thing we did was go to Camp Pendleton to hang out with some sergeants that were just about to be deployed, that was an eye-opener.
"I was blown away by these guys."
The 24-year-old actor played Logan Thibault in the film, a soldier fighting out in Iraq.
The former High School Musical star added: "The more I thought about it and researched it, I realised that if I ever was to have the chance to play a marine and to fill these shoes, that this is probably it."
Watch Digital Spy's interview with Zac Efron below:
