Filmmaker Kathryn Bigelow went into "The Hurt Locker" with two looming challenges. First, there was the perception that no Iraq War movie had succeeded at the box office. Second, her main cast was made up of talented working actors, but none were exactly household names. And yet the film, about the members of an elite bomb disposal unit, has gone on to become a critical and commercial success.

The film hinges on the chemistry of its three leads: Jeremy Renner as the reckless Staff Sgt. James, Anthony Mackie as the responsible Sgt. Sanborn, and Brian Geraghty as the more sensitive Spc. Eldridge. Working together on a tough three-month shoot in Jordan, the actors developed a bond that is palpable onscreen.

The Auditions

Renner, most recently seen in the ABC series "The Unusuals," has appeared in popular fare like "S.W.A.T." (as Colin Farrell's villainous ex-partner) and "28 Weeks Later" (as a heroic soldier). But it was his turn as serial killer Jeffrey Dahmer in the 2002 indie "Dahmer" that caught Bigelow's eye. "Kathryn fought for me from the get-go," Renner says. "She told the writer and handed him 'Dahmer.' He started watching and was like, 'This is Will James?' So she showed him some other roles with a little more personality. She's been my champion all through the process."

Mackie, who portrayed rapper Tupac Shakur in the 2009 film "Notorious"—and on stage in the play "Up Against the Wind"—originally was brought in to audition for Eldridge. "But I really wanted to be Sanborn," he admits. "Sanborn was, to me, the most dynamic character. I felt he had the arc of simple humanity. That was something I felt I hadn't been able to do, and as a young black actor you hardly ever get that opportunity."

Geraghty says he went into his audition for Eldridge completely unprepared. "I was so busy working on this little independent film ["Krews"], and I felt I owed it to that film not to concentrate on anything else," explains the actor, who also appeared in the war film "Jarhead." But his manager convinced him to take a meeting with Bigelow. "I show up to Kathryn's house, and I see notable actors sitting outside. I thought it was just a meeting, and they gave me two scenes and asked me to read with Jeremy. So I just went for it." By his own admission, it wasn't great. "[Screenwriter] Mark Boal jokes, 'You were the worst audition we saw.' But Kathryn says she saw me outside and saw me walk by and said, 'That's the guy.' " Geraghty says his cluelessness kept him from getting nervous. "I was just so oblivious because I was working. Had I known what I was going into, I probably would have ruined it."

The Training

The actors were sent to Fort Irwin, in California's Mojave Desert, to learn weapons training and about C-4. Geraghty already had experience from "Jarhead" but needed to learn the technical jargon. "We had to be very specific about how this team works—what exactly is my job amongst these three guys," he notes. "My most important part of the preparation was I talked to a guy there who had lost his team leader. I said, 'I don't want to pry, but if you want to talk about it, I would love to get this right and bring honesty and truth to this part.' "

The Relationships

Geraghty and Mackie had appeared together in the 2007 football drama "We Are Marshall," playing best friends. "To us, Jeremy was the outsider coming in," Geraghty notes. "Which worked great for the movie, because his character is new to the group at the beginning."

The trio quickly became good friends. Says Renner, "We needed each other; we leaned on each other. They're both very affable and funny, great human beings. As actors, you can't find more giving, complicated actors out there. They're so, so good." Being far away from home helped seal the bond. "You have to realize too, none of us had been to the Middle East, and that also forced us to become very close very quickly," Renner adds, "because we had this shared experience that's new for all of us, and so we kind of clung to each other in that way."

Even though it was a tough shoot, the actors wouldn't have it any other way. "We were really in it, three miles from the Iraqi border," Mackie reveals. "We weren't even acting most of the time. It was grueling wearing fatigues and 20 pounds of Kevlar in 120 degree heat. But it was a great experience I wouldn't trade for anything."

Adds Geraghty, "When we were making the film, we said, 'Who's going to see this?' But you know, I'm working with two of the best actors of my generation, doing amazing work in a film from someone as incredible as Kathryn Bigelow."

Echoes Renner, "It's been a really interesting journey. There's 9,000 reasons why this film shouldn't be made: No Iraq War film has done well, you've got three emerging faces, there's no real big stars in it—the list goes on and on. But I love that idea of being the underdog; I love clawing and scratching up your way to the top and trying to make something really good."