The year was 1592. After more than a century of bloody internal fighting, Japan had come through the Sengoku or "Warring States Period" and was united under the leadership of the warlord and commoner Toyotomi Hideyoshi.

Planning the Invasion

Hideyoshi needed an outlet for his warriors' energies. With peace at home, and thousands of battle-hardened samurai at his disposal, Hideyoshi turned his attention to thoughts of conquering Ming China, the region’s superpower.

The easiest way to conquer the Ming, he thought, would be to go through their tributary state, Joseon Korea. After Korea and China, Hideyoshi mused, perhaps he would take India...

Hideyoshi had every reason to suppose that his samurai could easily defeat the Joseon Koreans and the Ming Chinese. The Japanese troops had known only warfare, for all their lifetimes, and their fathers’ and grandfathers’ lifetimes as well.

Korea, on the other hand, had been at peace for centuries, and Korean energies were devoted to poetry, music, calligraphy, and other peaceful arts. One historian wrote (with some exaggeration) that “The story of Korean arms is a tragedy... It is the story of a people who repeatedly had to lay down their honored pen and brush to defend their lands and homes against those who loved the sword.” (J.L. Boots, 1934)

Hideyoshi had a healthy respect for the Ming Chinese, who possessed both immense numbers of troops and advanced military technology. Nonetheless, he felt sure that his samurai could quickly overwhelm them before the unwieldy Chinese bureaucracy could respond.

In addition, the Japanese had a new style of firearm, the arquebus musket, which they got from Dutch traders, then copied and improved.

The Samurai Invasion

Initially, everything went Japan’s way. A force of 7,000 Japanese sailed to the port of Busan, on Korea’s southeast coast, on April 13, 1592, and sacked the city after a short siege. By June 10, this initial Japanese division had been joined by eight more, and they were knocking down the doors of King Seonjo’s palace in Seoul. (The king had already fled north to Pyongyang.) Thus began the seven-year-long Imjin War.

On July 24, 1592, the Japanese captured Pyongyang (now the capital of North Korea). Korea’s leadership fled still further north, to the Yalu River that marks the boundary between Korea and China. There, they sent urgent messages to the Ming court requesting military aid. China responded with a small force of 5,000, but one arm of the Japanese army penetrated as far north as the Jurchen area of Manchuria before the tide began to turn.

Admiral Yi to the Rescue

In its drive up the Korean Peninsula, the Japanese army depended upon its navy to supply it with food, ammunition and reinforcements. Korea faced the prospect of imminent extinction, and morale was very low. Admiral Yi Sun-sin, Naval Commander of the Left of Jeolla Province, decided to strike a decisive blow against Japanese naval shipping. He knew that he could not defeat the Japanese army single-handedly, but he could certainly hinder them.

On August 14, 1592, Admiral Yi set out to attack the Japanese fleet, commanded by Wakisaka Yasuharu, as it made its way along the southern coast of Korea near Geoje Island.

Wakizaka’s fleet of 73 ships included 13 small scouting ships called kobaya, 24 mid-sized seki bune, and 36 multi-decked atakebune. It was a formidable assemblage, but the Japanese ships carried few cannon. Japanese naval ships generally ran down their opponents, grappled and boarded them, rather than trying to demast or sink them with cannon-shot.

Admiral Yi had only 56 ships at his command, most the 70- to 100-foot triple-decked panokseon, which carried shields around their decks much like Viking longboats had done. Yi also had two or three of the now-famous “turtle ships.”

Many popular accounts of the battle actually credit Admiral Yi with the invention of the turtle ship, but the idea first appears in Korean sources as early as 1415. The turtle ships were covered with overlapping spiked iron plates (hence the name), and featured a dragon-like head at the front. Sailors stoked fires below deck and funneled the smoke up through the dragon’s jaws, creating a terrifying spectacle. The ships were propelled both by fore-and-aft sails and by rows of oars on each side, making them more maneuverable than the Japanese square-sailed ships. They also carried cannon on both sides, a distinct advantage over the Japanese sailors’ muskets, bows and catapults.

The Battle of Hansan-do

Wakisaka’s fleet lay at anchor in the Gyeonnaeryang Strait between southern Korean and the large island of Geoje on the morning of August 14th. Admiral Yi ordered six of his panokseon to draw out the Japanese fleet from the channel; Wakisaka weighed anchor and sped out into open waters in pursuit.

When the panokseon and their pursuers reached the area near Hansan-do, the Japanese saw a fleet of nearly 50 additional Korean ships laying in wait. Admiral Yi deployed in the innovative “crane’s wing” formation, in which his fleet formed a boomerang shape that enveloped the Japanese ships, and peppered them with cannon-fire from both sides.

Wakisaka desperately tried to close with the Korean ships, but their shields and armor made grappling difficult. He sped his fleet ever closer into the center of the crane’s wing. The lightly-armed Japanese ships, though, were no match for the Korean fleet with its cannons.

Smoke poured out of the cannons, and the turtle ships' mouths. Flaming arrows, cannonballs, and musketballs filled the air. By mid-afternoon, 47 of the Japanese ships were at the bottom of the ocean, and an additional 12 had been captured by the Koreans. Approximately 8 - 9,000 Japanese sailors were killed. Admiral Yi lost not a single ship, and his casualties numbered only 19 killed and just over 100 injured.