Korean History › Late Joseon › Admiral Yi Sun-sin
Turtle ship (geobukseon)
used 1592–1598 (exact design debated)· Invention or discovery· Wars & invasions
Mostly agreedGood evidence; some details, dates or numbers uncertain.
A covered, spiked, cannon-armed Korean warship used by Yi Sun-sin to smash into Japanese fleets.
See it on the Korean History map →What happened
The geobukseon (거북선) was built on the panokseon, Joseon's standard two-deck oared warship. A covered top studded with spikes stopped boarding, Japan's favored tactic, and a dragon head at the bow could fire cannon or smoke. Cannons fired from all sides. A turtle ship is mentioned in 1413, but Yi Sun-sin's version was test-fired the day before the 1592 invasion. Only a handful, perhaps three to five, served; they led charges while dozens of panokseon did most of the fighting.
Why it matters
It became Korea's symbol of ingenuity and naval defense, and it helped Yi's fleets win by breaking Japanese formations early in battle.
How we know
Yi Sun-sin's reports and diary, two drawings in his 1795 collected works, and Japanese accounts of armored 'blind ships'; no original hull survives.
Still debated
Its exact layout, number of decks, and whether its roof was iron-plated (making it an early 'ironclad') are debated; replicas differ.
Connections (2)
▸Admiral Yi Sun-sin used Turtle ship (geobukseon)Well documented
The connection
Yi Sun-sin and his officer Na Dae-yong revived an old idea, building turtle ships on panokseon hulls for the Jeolla Left Navy. Yi test-fired one's cannon the day before the invasion and used turtle ships as shock ships to break enemy lines at Sacheon, Hansan Island and other battles.
When and how
Built at Yeosu, the Jeolla Left Navy's base, in 1591–1592; first used at the Battle of Sacheon in July 1592.
How we know
Yi's diary records the cannon test on the eve of war, and his battle reports describe the ships in action.
Debates and open questions
How much of the design was Yi's, Na Dae-yong's, or a revival of the 1413 turtle ship is unclear.
▸Turtle ship (geobukseon) fought at Battle of Hansan IslandWell documented
The connection
At Hansan Island, once the Japanese had been lured into open water, turtle ships charged into their line alongside the panokseon, firing cannon at close range and breaking the formation, while their spiked roofs foiled the Japanese tactic of boarding.
When and how
August 14, 1592, off Hansan Island; probably two or three turtle ships in Yi Sun-sin's fleet of about 55.
How we know
Yi's reports describe turtle ships charging ahead in the 1592 campaigns, including this one; Japanese accounts describe armored 'blind ships.'
Debates and open questions
How many turtle ships fought, and how decisive they were compared with the panokseon and the formation, is debated.