For two months before shooting began on this month’s action thriller Hanna, 17-year-old Saoirse Ronan endured a daily four-hour regimen of martial arts and weight lifting to play a girl trained by her father—a former Central Intelligence Agency operative (Eric Bana)—to assassinate a top CIA official (Cate Blanchett). It’s not the first time Ronan has been called upon to portray a kid with very adult challenges. In Atonement, for which she earned an Academy Award nomination, she played 13-year-old Briony Tallis, whose rape allegation dooms the love affair between Keira Knightley and James McAvoy. In Peter Jackson’s The Lovely Bones, she was 14-year-old Susie Salmon, who narrates her own murder investigation from beyond the grave. Yet to Ronan’s surprise, she found some childlike elements in the character of Hanna. “At first I thought, This is going to be a badass kid,” says the Irish actress. “But she turned into something else, which was actually quite innocent.” Although Hanna is very much an action movie (set to a thumping Chemical Brothers score), it’s also a coming-of-age story, to which Ronan can relate. “I’m still figuring out who I am,” she admits.