What is the author's style in Unbroken: A World War II Story of Survival, Resilience, and Redemption by Laura Hillenbrand?

Unbroken is a non-fiction biographical account of Louis Zamperini's experiences before, during and after World War II. It is told mostly from his perspective, relying extensively on interviews conducted by the author with Zamperini. Related events for which Zamperini was not present have been filled out by interviews with family members of Zamperini and other people who went through similar things.