"I was sort of aware of it," she tells TimeOut. "I would read 'A drone attack on ... .', but I never really thought about what that actually was, or where it's going to go in the future, and I learned a huge amount doing this. I think the size of the drones surprised me the most. The tiny little ones that can fly in through a window and watch you. That's not a fantasy. And if they're like that now, what are they going to be like in 20 years' time?"
The driving conflict in Eye In The Sky is whether to risk the life of a young girl selling bread on the street outside the terrorists' hideout.
"[Colonel Powell] is trying to protect the people who are at that moment shopping in a mall. She knows that these terrorists are about to blow up 150, 200 people, including children. She has to make that judgment: 'Do I allow them to do that?' I think it's the question all of us will ask when we leave the cinema, 'What would I have done?' I think I would be a coward and leave it to somebody else."
Eye In The Sky offers a modern portrayal of the military.
"There are more women in the military than we sort of really have taken note of. Including in the Islamic countries ... In Britain, the military was very much an Old Boys Club and women were not welcomed into it at all. And there are still great problems, mostly to do with sexual abuse of women in the military.
"It's funny, the arguments against having women in the military were never related to sexual abuse. They always said if you have a woman on the frontline, the soldier will care more about taking care of her than attacking the enemy, which is absolutely not what happened at all. It was the opposite. But you know, attitudes change, and it's great to see them change."
The film was one of the final projects for Rickman, who died in January, though he and Mirren didn't share any scenes.
"I knew Alan, I'd worked with him before and I'm very happy to be in a film with him and I think he would be very proud of this film."
Film preview
Who: Helen Mirren
What: Eye in the Sky
When and where: At cinemas from today