For Boal, who won an original screenplay Oscar for "Hurt Locker," the project was something he was already heavily invested in.  As he notes, "I'd been going around saying they were never going to get bin Laden for about three years so it was…it was a very emotional moment not for any professional reason, but just personally.  We were all sort of married to the material at that point and I think we both decided to try and hop on this news story and so, that's what we did. We started researching the intelligence hunt that lead to bin Laden's eventual demise and really we tried to capture the history the best we could in the context of the drama. But, hopefully, [also] capture this moment in American life and make something that because it's su h a heavy topic in a way and hopefully stands up to the test of time. So, five or 10 years from now they could look back on this and say, 'Hey, they more or less got this right.'

Boal was also very aware that if they didn't act quickly, competing TV movies and other film projects could beat them to the punch.

"We kind of felt like we had paid our dues on this subject and [wanted] our chance to have it pay off. So, for the last year we have all been working really long hours to get this done," Boal says. "And also make sure it wasn't just a history lesson. That's what I think the actors did so amazingly - find the moments of human passion and human pain within this larger skeletal frame."

It became clear that casting the role of Maya was going to be essential for the picture. Bigelow first caught wind of Chastain's talents after she screened a rough cut of Ralph Fiennes' underrated adaptation of "Coriolanus." She was Bigelow's first choice, but there was a scheduling issue, but, as the director notes, "Thank god the movie gods and the good graces of Universal were able to move another production she was already committed to.  I'm extremely graceful."

The always charming and honest Chastain was working on a project in Toronto when she was first approached about "Thirty" by producer Megan Ellison, who also shepherded another Chastain picture, "Lawless."  The next thing Chastain knew she was cold-called by Bigelow herself, a woman she says has "always been a big hero of mine."

"I'm listening to my phone and I'm listening to this message and I just freaked out," Chastain says. "I then calmed myself down [and in a formal and calm British voice] 'Yes Kathryn, it would be a joy to read the script.' (Laughs.) And there was a very secretive way to read the script. You had to check in on a website and it felt like you were on a secret mission.  And I remember I was half-way through and I had to go to another meeting.  And I got in my car and I realized I was in character and driving like I was in a spy movie. (Laughs.) That's when I realized the part was mine and all other actors beware, I must play it."

Maya is an expert in the Islamic world where the hunt for Bin Laden takes place and that means dialogue full of Arabic names and references that any Western actor would need a lot of training for. Chastain admits there was no way she was ready to film the day after she was cast. In fact, she describes "Thirty" as the "most difficult thing I've ever done."

"I was cast in December and that's when the training started which was not light, easy information. A lot of facts I don't necessarily know in my vegan, hippie self," Chastain jokes. "And we were in rehearsal in Jordan and I was very lucky to get awards attention for 'The Help' and I came back for the Oscars and the next day at noon I got on a plane. The day before I was in a dress with my grandmother at the Oscars and then I was on a 25-hour flight to Chandigarh, India. We land and I made a joke, 'OK, when do we start guys?' And Mark says, 'OK, come to set.' (Laughs.) And the next thing I knew I was in a market."

"Thirty" is based on a lot of first hand accounts and there was a woman Chastain portrays who was key in finding bin Laden. However, unlike the now long retired Tony Mendez from "Argo," it will likely be decades until you learn her or any of the other agents' real names.

"All of the people who are depicted are based on real people," Boal says. "That being said, it's not a documentary. It's not word for word. But, hopefully it captures the spirit and it I think tracks pretty closely to what is known of the intelligence hunt and reveals some things that might have been misunderstood. And, most of all, because so much of this stuff is done in the shadows, unless you've read every single book and read every single article this is the first time it's been pulled all together and brought to the screen. A lot of it was informed by real life, but we couldn't ask CIA agents to give us their identities. They are still working, by the way."

And of course, the follow-up question has to be: have these real CIA agents seen the movie yet?

Boal smiles and says, "This is probably the first audience that has seen the movie, but knowing how they work I really can't say. (Laughs.)"

On a serious note, though, Boal made a striking observation about what surprised him the most researching this story.  And it's one reason why bringing this tale to the screen under the talented eyes of a visionary such as Bigelow was so important.

"The thing that surprised me the most was the role of women in this story," Boal says. "Maybe I just grew up reading too much Bond, but I just didn't know that was part of the deal. I think it's ironic that al-Qaeda, that for the leader of al-Qaeda was in some sense defeated by the spectre that they feared most, right? A liberated, Western woman."

And no matter what the box office or awards season response to "Thirty" turns out to be, the fact the film will spread that message throughout the world may be its greatest achievement.

"Zero Dark Thirty" opens in limited release on Dec. 19 and nationwide on Jan 11.