Admiral Yi Sun-sin's Turtle Ships Repel Hideyoshi's Invasion

What happened

In 1592 Toyotomi Hideyoshi, having unified Japan, launched an invasion of Korea as the first step toward what he told King Seonjo was a plan to conquer all of Asia. More than 150,000 Japanese troops, many carrying muskets Korea lacked in quantity, landed at Pusan and reached Seoul within three weeks. Admiral Yi Sun-sin, commanding Korea's Left Naval Station at Cholla, had already been improving Korean naval readiness and rushed out a design building on earlier Korean cannon-ship experiments: the geobukseon, or turtle ship, roughly 110 feet long, with an enclosed, roofed upper deck studded with concealed spikes and covered in straw to disguise them, protecting oarsmen and gun crews from arrow and musket fire while mounting as many as forty cannon. Rather than let the Japanese board and fight hand-to-hand, where their swordsmen excelled, Yi kept his faster, longer-ranged ships at a distance and battered Japanese vessels with cannon fire. At the Battle of Hansan Island in 1592, Yi lured the Japanese fleet into open water with a feigned retreat, then encircled it in a crane wing formation, burning 73 enemy ships in what Korean accounts call the Great Victory of Hansando. Yi never lost a naval battle during the seven-year war.

How we know

Yi Sun-sin kept detailed campaign diaries and official reports to the Joseon court that survive as primary sources, supplemented by a contemporary biography written by his nephew describing battle tactics such as the crane-wing formation at Hansan Island.

Sources

• Association for Asian Studies (Education About Asia). Admiral Yi Sun-Shin, the Turtle Ships, and Modern Asian History · General sourceasianstudies.org · Cited as a "reference" source (no stronger domain match).
• U.S. Naval Institute, Naval History Magazine. Complementary Keys to Naval Victory · General sourceusni.org · Cited as a "reference" source (no stronger domain match).