The film mainly follows the famed 1597 Battle of Myeongryang during the Japanese invasion of Korea (1592-1598), by which the iconic Joseon admiral Yi Sun-sin were able to destroy a total of 133 Japanese warships with just 1-3 ships staying within his command. The battle, which happened from the southwest coast of the Korean Peninsula from the Myeongryang Strait, is thought to be one of the most significant victories of Yi.