Joseph fiennes lost 20 pounds to star in this film. Captain Prince's prototype was still alive when the film was being filmed. For this reason, James Franco met Prince, an old man living in Seattle, and began to watch documentaries and interview videos in the 1940s. The filming of the film took four months, including the rescue battle scene for one and a half months. In order to realize the physical and mental integrity of officers in World War II, the crew hired a Vietnam War veteran for Benjamin Bratt and James Frank to take charge of special training and learn how to make battle plans and give orders. On the eve of filming, james frank specially watched the 6-hour live interview video filmed by the director for Captain Prince, in order to ponder the words, demeanor and mentality of the role prototype in the rescue mission and faithfully reproduce the heroic deeds of historical figures.