Towards the end of the 16th Century, the civil wars which had plagued Japan for decades came to an end.

Toyotomi Hideyoshi, a Japanese samurai, a member of the ruling military nobility, and daimyo (a feudal lord) emerged victorious.

Having unified his country, he looked to build on this success and show his military and naval power.

He turned his attention to conquering China, ruled at that time by the Ming dynasty, and Korea, which was ruled by the Joseon dynasty.

It is clear that Hideyoshi had planned for a possible war with both China and Korea long before he completed the unification of Japan.

It is believed, that he ordered the construction of as many as 2,000 ships as early as 1586.

He planned to invade Korea first and use the Korean peninsula to invade China.

As a first stage, in 1587, he sent envoys to Korea to persuade the Joseon ruler, King Seonjo, (ruled 1567-1608) to join him in a war against China.

However, he was impatient and quickly followed that approach with an ultimatum that unless Korea submitted to Japan and participated in the conquest of China, Korea itself would be attacked and conquered by Japan.

Hideyoshi’s tactics did not work. The Koreans would not submit to him and, as a result, in 1592 he launched his armies against Korea.

Although the war lasted until 1598, it was divided into two phases from 1592-3 and from 1597-8.

At the moment that Korea faced defeat on land and occupation by a foreign power, it found its saviour in Yi Sun Sin and his deployment of the Korean navy, especially the Geobukseon, or turtle ship.

Yi had joined the army as an officer in 1576 and over the next 15 years he showed his skill as a warrior and a leader.

In March 1591 he was appointed as commander of a naval district, and he took up his post at the port of Yeosu.

Here he focused upon strengthening the regional navy including the construction of the turtle ship.

After the Japanese attached Korea in 1592, Yi deployed his ships against the invaders and, although he had never led a fleet into battle before, he won several quick victories.

Hideyoshi needed command of the seas, so Yi’s’ victories made him realise the danger that Korea posed.

Although the Japanese hoped to overwhelm the Koreans by having superior numbers of ships, this tactic did not work.

Despite being outnumbered in battle, the Koreans were victorious in every single engagement with the Japanese at sea and won at least 15 battles in 1592. This resulted in thousands of Japanese naval casualties and hundreds of sunken Japanese warships and supply ships.

It appears that the Koreans lost very few ships.

Yi was successful for several reasons.

He had prepared well and ensured that there were sufficient supplies for his navy.

The Korean panokseon ships, wooden vessels powered by sail and oars, were also stronger than Japanese ships.

They were superior in construction, carried five times as many cannons as the Japanese boats (20 to 4), and the Korean cannons outgunned the Japanese ones in terms of power and range.

He also used a particular strategy by luring the enemy to chase his ships.

At a given signal his ships created a crescent or crane wing formation – the hakikjin strategy – which enabled his fleet to partially surround and destroy the enemy.

Yi was also a charismatic leader.

It is said that he respected his men, would fight alongside them and generally do what he could to maintain their morale.

He was also a capable strategist and used his knowledge of the Korean coast and tides to plan his attacks.

However, perhaps the principal reason for his success was that he used the turtle ship to great effect.

Yi did not invent the turtle ship but improved older designs that had been suggested during the late Goryeo dynasty (lasted 918-1392) and the early Joseon dynasty, in particular the reigns of King Taejong (ruled 1400-1418) and King Sejong (ruled 1418-1450).

A scaled model of the turtle ship in The Saga Prefectural Nagoya Castle Museum in Karatsu, Japan © Dr Stephen Turnbull

In effect, Yi developed the design so that the boat could be used much more effectively and extensively in actual combat.

Korean and Japanese accounts of this period refer to turtle ships.

However, no ship has survived, and there is still debate about what turtle ships looked like and whether they had an iron plate placed over the boat to help protect the sailors.

There is, though, agreement that they were turtle-shaped and equipped with many cannons, eleven on each side and two each at the stern and the bow.

The ship’s figurehead was in the shape of a dragon and held up to four cannons.

A scaled model of the turtle ship in The Saga Prefectural Nagoya Castle Museum in Karatsu, Japan © Dr Stephen Turnbull

During a battle, smoke was released though the mouth of the dragon which was intended, together with its fierce appearance, to frighten opponents.

The sides of the turtle ship had small holes through which arrows and guns could be fired.

The Korean strategy was to fire their guns and cannons at a range which would prevent the enemy coming close enough to board them.

If an enemy warship managed to come alongside, the roof of the turtle ship was covered with wooden planks on which were placed rows of spikes.

These spikes were there to prevent the ship from being boarded because Japanese ships were taller out of the water and so sailors wishing to board would have to jump down onto the roof and risk serious injury.

A replica of the Turtle Ship (scaled model 1:2.5) in the War Memorial of Korea Museum, Seoul

Each turtle ship had two large sails, one on each of the two masts, and was powered by 20 oars each pulled by two men during fine weather and five men in rough weather or battle.

The ship had multiple layers to separate the rowers from the cannons.

Turtle ships were mostly used to spearhead attacks and were best used in tight areas, for example, in straits and around islands, rather than the open sea.

The turtle ship was such a success because it had superior fire-power and structural design.

The iron spikes on the roof, cannons placed at every angle and the emission of smoke from the dragon’s head to frighten and provide cover all combined to help the turtle ship win in battle.

In addition, the ship was well-suited for ramming, as it was stronger than the Japanese ships due to the use of red pine timber and wooden nails which expanded as they absorbed seawater, thus making the ship as watertight as possible.

Following intervention from Ming China in 1593 to support Korea, the Japanese gradually retreated and by the end of the year most Japanese soldiers had withdrawn from the Korean peninsula.

The years 1594-96 saw a series of peace negotiations but they failed to produce a peace settlement.

Toyotomi Hideyoshi had not given up on his desire for overseas conquest and in 1597 war resumed with the Japanese again invading Korea, this time though with the intention of just conquering Korea.

The Koreans were better equipped and prepared, and Ming China provided immediate and much needed support.

It was clear that the navy under the command of Yi Sun Sin would again play a decisive role in defending Korea by firstly interrupting attempts by Japan to land men and resources and secondly disrupting any supply ships.

It was at this point that Yi was faced with a major decision.

As a result of information from a Japanese double spy – that is one who was pretending to spy for Korea but was actually working for Japan – Yi was ordered by the government to undertake a surprise operation against the Japanese navy.

Doubting the reliability of the information because it indicated that he would have to sail his fleet through dangerous shallow waters, Yi concluded that the Japanese were setting a trap for him and his ships.

As a result, he refused to obey the order.

His enemies at court who were jealous of his success persuaded King Seonjo to demote and jail him for disobeying orders.

A replacement – Won Gyun – was appointed as commander of the fleet.

However, without sufficient preparations and planning, the new commander launched the entire Korean navy – almost 100 ships – against the Japanese navy.

At the subsequent Battle of Chilcheollyang in August 1597, Won Gyun was completely overwhelmed by the Japanese and all but 13 of his ships were destroyed.

Won Gyun was also killed.

This battle was Japan’s only decisive naval victory of the war.

The Japanese could now land their troops on the Korean peninsula without disturbance.

Realising the seriousness of the situation, King Seonjo released Yi and reinstated him as head of the navy.

Yi set about reorganising and reequipping his ships and in October 1597 he again faced the Japanese navy at the battle of Myeongnyang.

Despite only having 13 ships, he routed a much superior force of 133 warships, destroying 30 ships and severely damaging a further 30, and without losing any of his own ships.

As a result of the difference in the size of the fleets, the battle of Myeongnyang is considered Yi Sun Sin’s greatest victory.

The war continued on land and at sea for another year.

With the death of Toyotomi Hideyoshi in September 1598, though, the Japanese decided to end the attempt to conquer Korea and in October they ordered all their forces to withdraw from the peninsula.

One further sea battle took place in December 1598 and turtle ships again played a key role in the Korean victory at the battle of Noryang.
However, during the fighting Admiral Yi Sun Sin was killed.

Following the battle of Saechon in July 1592, Admiral Yi related what had happened to King Saejon.

He wrote in his report: “Previously, foreseeing the Japanese invasion, I had a turtle ship made…with a dragon’s head, from whose mouth we could fire cannons, and with iron spikes on its back to pierce the enemy’s feet when they tried to board.

“Because it is in the shape of a turtle, our men can look out from inside, but the enemy cannot look in from outside. It moves so swiftly that it can plunge into the midst of even many hundreds of enemy vessels in any weather to attack them with cannonballs and fire throwers.”
Stephen Turnbull, 2002

The turtle ship helped to save Korea at this time from complete defeat and occupation by the Japanese.

Although turtle ships were the most important part of Admiral Yi’s’ fleet, he never used more than five in any one battle.

As a result, they were only ever in a minority within the ships of the Korean navy.

They were used in all 15 naval engagements between May 1592 and March 1593, in what was the first phase of the Japanese invasion of Korea.

They were not used widely in the second phase invasions in 1597-98 apart from the decisive Battle of Noryang in 1598.

The turtle ship continued to be part of the navy for the following three centuries but with changes in design and tactics they were gradually replaced by more sophisticated vessels.

As for Admiral Yi, he was victorious in all the 23 battles against the Japanese invaders, and this is an unprecedented achievement in world naval battle history.

In most of these battles, he was outnumbered and lacked necessary supplies, but he was able to outsmart his enemies even when the odds were stacked against him.

He is regarded as a great naval commander, and he is revered in Korean history for his heroic actions in rescuing his country from near ruin during the Hideyoshi Invasions.

We know so much about him and the war against Japan because his diary of the period 1592-1598 has survived.

It describes in detail the “daily combat situations, the admiral’s personal views and feelings, observations on the weather, topographical features of battlefields, and the lives of common people” and is regarded as “without equal in world history as a commander’s battlefield account”.
Nanjung Ilgi, The War Diaries of Admiral Yi Sun-Sin

The historian Stephen Turnbull regards Yi as “the greatest hero of the defeat of the Samurai invasion of Korea” and “one of the outstanding naval commanders in the entire history of the world”.
S Turnbull, The Samurai Invasion of Korea 1592-98, Osprey Publishing; 1st edition (2 July 2008), page 5

Yi is celebrated as a national hero, with numerous statues in his honour, as well as numerous films and documentaries focussed on his exploits.

The statue of Admiral Yi Sun Sin, on Sejong-daero, Gwanghwamun Plaza, Seoul

In Seoul a statue to him dominates Gwanghwamun Square and at its base is a model of the turtle ship, the weapon he used so successfully in defence of his country. 

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