The story of the movie is based on a true history of World War II: in 1942, a Japanese cargo ship "Lisbon Maru" loaded with more than 1,800 British POWs was torpedoed and sunk by a U.S. submarine in the waters near Zhoushan Islands. Nearby fishermen from the East Pole risked their lives to rescue more than 300 British soldiers, and protected and rescued three Britons during a massive search by the Japanese. This history is known as the "Lisbon Maru Shipwreck Incident".