The film revolves around the titular
Battle of Myeongryang around 1597, which is regarded as one of legendary
Joseon Admiral
Yi Sun-sin's most remarkable naval victories. He led only 12 ships under his command to a heroic victory against an invading Japanese fleet of 133 vessels. At the onset of the battle at their base in
Haenam, the
Japanese invaders under
Tōdō Takatora are confident that their
planned expedition to
Hansong to capture King
Seonjo will be rather straightforward. However, they remain reserved over the news that Joseon's greatest admiral,
Yi Sun-sin, has been restored to his former command after the
disaster at Chilcheollyang, which has reduced the Korean navy to a mere dozen battle-ready ships. To ensure the success of the operation,
Hideyoshi sends one of his finest naval war leaders to Joseon,
Kurushima Michifusa, the commander of the Murakami Clan Navy who is an expert in naval combat but enjoys a shaky reputation among his fellow
daimyō as a pirate. One of the admirals of the
Japanese Left Army,
Wakizaka, first meets Kurushima and his lieutenant, Kimura, while he finishes off the remnants of a group of Joseon soldiers. He especially distrusts Kurushima and draws his sword on him several times, especially after the latter insults him by shaming his
defeat at Hansan Island. Later, Kurushima and Haru, his
sharpshooter, drink
sake as Kurushima elaborates on his personal vendetta against Yi Sun-sin, stating that his brother Michiyuki had been
killed by the latter earlier in the war. In the meantime, Yi Sun-sin is facing the despair mounting among his officers and troops. Facing an enemy force that far outnumbers them and seeing no reasonable chance of success in the inevitable clash even with one single
turtle ship remaining, many consider the fight lost before it has even started. Despite his outwardly indifferent demeanor, Yi is hard-pressed to maintain morale among his men and desperate to find a solution to his problem. However, the breaking point seems to be reached when General
Bae Seol, the deserter of Chilcheollyang, burns the turtle ship and has his men try to
assassinate Yi. Although Yi escapes and Bae is killed for his act of treachery, the ship is lost, which boosts confidence among the Japanese and further dispirits Yi's troops. To seek an answer, Yi travels to the
Myeongryang Strait, an area notorious for its strong and treacherous currents, which the Japanese intend to cross on their way to Hansong. Later, he confides in his son
Hoe that to win the fight, he must turn the fear paralyzing his men into courage. Upon hearing that the departure of the Japanese attack fleet is imminent, Yi abandons his base and moves to Usuyeong after burning the naval facilities to the ground. The next morning, Yi's fleet arrives in the strait and is shortly met by the Japanese, who are using the morning tide to move into the channel, with Kurushima leading the vanguard. Yi engages Kurushima's fleet in battle, but as the other Korean commanders are still hesitant to involve themselves, Yi's flagship is quickly surrounded and attacked by
boarding parties. In the apparently hopeless situation, Yi commands several cannons to be fired from the rower deck's port hatches in a concentrated volley, to use their recoil to blast the ship free of its encirclement. As Yi had hoped, this bold act of survival inspires the rest of his countrymen to take the fight to the enemy. When the tide turns and forms a
whirlpool in the middle of the channel, thus solidifying Yi's defensive position, Kurushima orders an all-out attack with the rest of his ships. Despite the efforts of Haru and a ship
loaded with black powder charges, the renewed courage of the Koreans prevails, though heavy sacrifices are made. Kurushima's desperate situation is observed by Todo, who merely laughs at
Katō's suggestion of reinforcing him. Kurushima, realizing that he is now on his own, boards the Korean flagship but is decapitated by Yi himself after he takes several arrows from Korean
archers, and his head is hung from the tip of the ship's mast. When Yi's ship itself is caught in the whirlpool, his civilian navy servants and local fishermen courageously drag the vessel back to safety. Joined by the rest of the fleet, Yi leads a counterattack that deals the Japanese forces a crushing blow, forces them into retreat, and leaves the Koreans triumphant. The film ends with a reminiscence of the first encounter of the Japanese with the turtle ship in 1592. == Historical background ==