Battle of Sacheon: Korean Navy Using a "Turtle Ship" Defeats Japanese

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Battle of Sacheon: Korean Navy Using a "Turtle Ship" Defeats Japanese

Battle of Sacheon, May 29, 1592
Artist unknown, from website
(Unless otherwise indicated, all illustrations are from Wikipedia)

Today in Military History: May 29, 1592

For today's mini-history lesson, we go to the Far East to comment upon a naval battle between the Japanese and the Koreans. It features a unique naval vessel which proved to be the decisive element in repelling an invasion of the "Hermit Kingdom" of Korea.


By the late 16th century, a certain amount of unity was achieved on the Japanese archipelago. The emperor was a weak figurehead, with true political power being wielded by a number of warlords, called daimyo, who fought to become the supreme warlord, or shogun. In 1592, Toyotomi Hideyoshi, a low-born son of a peasant foot soldier, fought his way to the top of the Japanese political food chain. Hideyoshi made alliances at need, but also was a well-trained fighting man. He fought in many battles between 1560 and 1590, building or repairing a number of castles throughout Japan. In 1585, he was given the title of kampaku, or regent, to the imperial court. Because of his lowly social class, he was ineligible for the title of shogun.

In his later years as his health began to falter – and he slowly descended into paranoia – Hideyoshi conceived a plan to conquer Ming China and give his countrymen sufficient lebensraum (living room) to expand. Beginning in 1587, the kampaku sent annual requests to the emperor of Korea, seeking passage through that nation in order to come to grips with the Chinese. The kingdom of Korea was a tributary of Ming China, therefore was bound to fight the enemies of their lords. The Korean ruler managed to put the Japanese off for several years, finally accepting a letter from Hideyoshi in 1591. After reading its contents, the Korean court sent word to the Chinese warning them of a potential invasion from Japan. Finally, after another Hideoyoshi letter to the Korean throne was ignored, plans went forward for an invasion of Korea. Once that nation was subdued, the next target would be China.

[The Koreans initially held the Japanese military in low regard, knowing of the clan warfare which raged throughout the mid- to late 16th century. The only other contact the Koreans had with the Japanese was the constant raids by wako, or Japanese pirates, on Korean ships.]

Portrait of Toyotomi Hideyoshi (1601), author unknown; Currently in the Kōdai-ji Temple, Kyoto, Japan
Portrait of Toyotomi Hideyoshi (1601), author unknown
Currently in the Kōdai-ji Temple, Kyoto, Japan

Japanese Navy and Tactics

In the three centuries since the Mongol invasions of 1274 and 1281, the Japanese became convinced of the necessity of building a navy to repel future invasions. [For more on the Mongol reconnaissance attacks against Japan, please see my Burn Pit posting of August 13, 2012 entitled: divinewindswreckmongolinvasion] The Japanese began developing several classes of vessels, mainly variants of merchant ships, which could carry large numbers of samurai and other fighting men, large-caliber arquebuses, but virtually no cannon.

Japanese atakebune, 16th century sketch, artist unknown
Japanese atakebune, 16th century sketch, artist unknown

The "dreadnought" of the Japanese navy was the atakebune. These vessels were at first only used in coastal actions, and may be regarded as floating fortresses rather than true warships. Early versions of this ship were described as "iron ships." This nomenclature is a bit confusing, as they were not fully ironclad, but may have used iron plates to protect the superstructure from enemy cannon fire and other missiles. They used oars for propulsion, as their iron cladding (if it existed) as well as their bulk (i.e. the armament and people they were carrying) likely impeded wind-based propulsion via sails.

Japanese naval tactics had not evolved in the 300+ years since the twin kamikaze (divine wind) miracles which saved their nation from the Mongols. Most Japanese warships carried large numbers of samurai and other fighting men; upon sighting enemy ships, they would row to intercept, grapple the enemy, and board them to essentially fight land battles on board. [As the war with Korea progressed, the Japanese would begin installing cannon on their ships, but found the vessels were too lightly-built to carry large numbers of artillery. Therefore, the Japanese were forced to "go back to the drawing board" to develop stronger ships.]

Korean Navy and Tactics

The Korean navy of this time was comprised of ships of various designs. These vessels generally had one feature in common: a flat keel. This feature was due to the nature of the Korean coastal waters, which have a large tidal range and flat, expansive tidal plains. A flat keel enables a ship to sit comfortably on the tideland when the tide was out, after coming ashore or inside a wharf at high water. It also ensured greater mobility and a shallow draft and in particular allowed a ship to make sharp changes of direction at short notice.

Sixteenth century print of a Korean panokseon (Illustration courtesy of Wikipedia, via
Sixteenth century print of a Korean panokseon
(Illustration courtesy of Wikipedia, via

The main workhorse of the Korean navy was the panokseon (meaning "board-roofed). It was a two- or three-decked ship – between 70 and 120 feet long – made of sturdy pine wood for the hull and oak wood for the frame and masts. Rather than using iron nails, bamboo pegs held the pine boards to the frames. This had the advantage of holding the frame together more effectively, as bamboo expands in water. This vessel was propelled by two sails and up to 20 oars, with 60 rowers and sailors, and as many as 125 Korean marines. It was also armed with a variable number and type of cannon (more about that below). The upper deck also sported an observation tower or command post where the ship's commander could have a panoramic view of the action.

The main advantage the Korean navy enjoyed over the Japanese was their use of cannon (usually referred to collectively as chongtong). The Koreans had developed a large number of cannon types in the 200 years before the Hideyoshi invasion. The panokseon used a number of different sizes of cannon and projectiles. The largest piece of artillery used was the cheonja ("heaven"), and was the standard cannon on the panokseon. It could fire stone or metal cannonballs between 385-550 yards. Other ammunition included an explosive round similar to shrapnel, or a daejanggunjeon, a large rocket-shaped arrow with an iron head and fins. The cheonja could fire one of these missiles nearly a mile, probably against the hulls of Japanese vessels.

Other types of artillery used by the Koreans included the medium-sized jija ("earth") and the smaller hyeonja ("black"). They also deployed smaller artillery pieces that were essentially large arquebuses.

Korean artillery (l-r): cheonjachongtong, jijachongtong, and the hyeonjachongtong; Each piece is armed with replicas of the daejanggunjeon arrow
Korean artillery (l-r): cheonjachongtong, jijachongtong, and the hyeonjachongtong
Each piece is armed with replicas of the daejanggunjeon arrow

In the years prior to the Japanese invasion, a secret Korean ship-building program was underway. Under the direction of Admiral Yi Sun-shin, a new and – to the Japanese – terrifying class of ship was produced. It was called the geobukseon, or "turtle ship," and Admiral Yi intended it to be a close assault naval weapon. It was based on a previously designed vessel of the early 15th century. Technically, it was an updated version of the panokseon.

The geobukseon was about 120 feet long, carried two sails and 16-20 oars for propulsion, with up to 70 men using the oars. It also had a U-shaped hull, which gave the vessel a tighter turning radius, and a more stable firing platform for its cannon. Its main armaments consisted of 20-26 cannon. It carried up to 22 cannon – likely the jijachongtong medium cannon – in two broadsides of as many as 11 pieces each, and 2 cannon each in the bow and the stern – probably the heavier cheonjachongtong. It also boasted a number of other windows or portals to allow the crew to fire arquebuses and bows at the enemy.

One of the turtle ship's unique features was dozens of hexagonal wooden panels which covered the upper deck, essentially a roof to protect the 50-60 marines and other crew, and to deflect arrow fire, musket-shots, and incendiary weapons. This roof was also covered with iron spikes, to discourage the Japanese from using their usual boarding tactics, as the Korean geobukseon sat much lower in the water than the Japanese atakebune. These spikes were hidden under thick straw mats prior to combat. [Some historians have claimed this roof was made of iron plates, but that statement is unsubstantiated.]

Reconstructed, full-sized model of a Korean turtle ship (Image courtesy of
Reconstructed, full-sized model of a Korean turtle ship
(Image courtesy of

Its most distinctive feature was the dragon's head at the bow. It was designed as a form of psychological warfare initially, to frighten superstitious Japanese sailors. However, it also was constructed to allow sulfurous smoke to issue from the figurehead's mouth, often to generate smoke screens to confuse Japanese lookouts and conceal the ship's movements. Some descriptions of the vessel say that the dragon's head could also accommodate a cannon – perhaps the smaller hyeonjachongtong – or a bowman or arquebusier. Some versions of the turtle ship also had a ram on the prow, sometimes described as a gargoyle, along with a large heavy anchor. All told, between 20 and 40 turtle ships were built and deployed against the Japanese.

Prelude to the Battle

Admiral Yi was at his headquarters in Yeosu, on the southwestern coast of Korea. The admiral had waged a first successful campaign against the invading Japanese in late April and early May, and was planning to attack them again. However, in late May Yi's fellow admiral Won Kyun sent a report to him that Japanese ships were in Sacheon located on the central southern Korean coast. This alarmed Admiral Yi because he feared the Japanese army was readying an attack on his base at Yeosu. Within days, Admiral Yi gathered and led his fleet eastward to Sacheon. His fleet consisted of 25 ships, mostly the panokseon and similar ships. In addition, Admiral Yi brought with him as his command vessel one of his first turtle ships.

Arriving outside the harbor of Sancheon, Admiral Yi observed that there was a considerable rocky ledge overlooking the entrance to the harbor. He also noticed that a number of Japanese bowmen and arquebusiers were clambering onto the ledge. These missile troops would likely play havoc with his other vessels.

Battle of Sacheon

When the Korean flotilla arrived at Sancheon, the tide was flowing outward, which would hamper the movement of Admiral Yi's force. Therefore, he decided to first to have his fleet stand to outside the harbor mouth, hoping to lure the 13 Japanese atakebune out into the open sea where he had more room to maneuver, as well as being away from any covering fire from the Japanese infantry.

After a few hours, the Japanese resisted the temptation of Yi's ships (I would not be surprised if the admiral had his turtle ship screened by his other ships, keeping the enemy in the dark about his new "secret weapon"). Admiral Yi then decided to throw the dice and gamble: he ordered his fleet to begin a slow withdrawal, again hoping to entice the Japanese into a fight. Even though sunset was near, the Japanese commander decided to catch the tide and pursue the apparently retreating Korean ships. Once they were several miles outside Sacheon harbor, Admiral Yi ordered his ships to reverse course and attack the pursuing Japanese – the hunted now became the hunter.

Admiral Yi's Naval Campaign during Japanese Invasion
Admiral Yi's Naval Campaign during Japanese Invasion

The Korean ships began a heavy barrage of cannon fire which initially took the Japanese by surprise. Undaunted, they began to return fire with arquebuses and bows, and tried to maneuver their vessels to grapple the Korean ships and send boarding parties. However, the concentrated volume of Korean artillery and bowfire prevented most of these attempted attacks. The large, unwieldy oar-driven Japanese atabukane could not turn as quickly as the Korean panokseon.

At some point during the battle, Admiral Yi's new brainchild, the geobukseon, emerged from the battlesmoke and sulfur fumes being projected from the dragon's head. Using both sails and oars, the turtle ship plunged directly into the middle of the Japanese fleet. As it did so, every piece of ordinance on the turtle ship began belching fire, smoke, and destruction, firing as quickly as humanly possible. Anytime the admiral's flagship got close to an enemy vessel, a few brave samurai jumped overboard and attempted to climb onto the roof of the turtle ship. But, for their trouble, they ended up impaled on the iron spike covering the wooden dome. Within two hours, the Korean flotilla had wiped out the Japanese squadron.


The entire Japanese fleet was sunk, with the loss of nearly all crews, though a few managed to swim to shore to report on the battle's outcome. According to Korean chronicles, Admiral Yi lost only 4 men to severe battle wounds. In addition, during the height of the battle, the admiral received a wound in his arm from an enemy arquebusier. Fortunately, the wound proved minor.

Footnote #1: The Korean victory took the Japanese by surprise, causing great worry about the fate of supply ships which would be coming from Japan. Admiral Yi conducted several more naval campaigns against the invaders from Japan. He destroyed enough warships and supply vessels to hamstring the operation. In fact, because of Yi's successful actions, Hideyoshi changed the objective of the operation from an invasion of China to the subjugation of Korea.

Footnote #2: Admiral Yi is considered one of Korea's greatest military heroes. He had a distinguished career in the army, but achieved his greatest fame on the water. Despite never having received naval training or participating in naval combat prior to the Hideyoshi invasion, and constantly being outnumbered and outsupplied, he went to his grave as one of few admirals in world history who remained undefeated after commanding as many naval battles as he did (at least 23). His career has been favorably compared to England Admiral Lord Horatio Nelson.

Statue of Admiral Yi, Seoul, S. Korea
Statue of Admiral Yi, Seoul, S. Korea

Footnote #3: The Koreans also used the hwacha, a device similar to a multiple rocket launcher, which could fire up to 200 fire arrow rockets at the Japanese ships. The usual targets were the sails or the large numbers of Japanese soldiers on the main deck. The device was also used extensively in land combat, especially for the defense of castles and other strongholds, but also in battles in which large numbers of closely-packed Japanese soldiers presented marvelous targets of opportunity.

Korean hwacha> rocket launcher (Illustration courtesy of
Korean hwacha rocket launcher
(Illustration courtesy of

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