The movie mainly follows the famed 1597 Battle of Myeongryang throughout 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 in his control. The battle, which took place off the coast of the Korean Peninsula from the Myeongryang Strait, is considered one of the most important successes of Yi.