The Korean Navy Strikes Back II




Korean Turtle ship 1592-1598

Yi Sun-sin was now a hero. He had delivered the first telling blow to the Japanese invaders and had given his countrymen a reason to hope that maybe, just maybe, they could drive them back across the sea. But he made it difficult for the government to honor him, for he spoke his mind too freely and questioned his superiors when he thought they were wrong. It had been his conviction since being appointed commander of the Cholla Left Navy in 1591 that the coming Japanese invasion should be met at sea, where Korea’s strength lay, and not on land as the government in Seoul intended. The government did not agree. Rather than beefing up the southern fleets as Yi urged them to do, they focused instead on building walls and fortifying southern towns. The overwhelming success of the Japanese invasion when it finally came was thus seen by Yi as all too predictable, and he could not help but point this out. “It may be a foolish thought,” he wrote in his dispatch of June 9, prior to sailing into battle, “but in my opinion the enemy attacks fiercely, trampling our fair land under iron feet, because we allowed him to set foot on our shores instead of fighting him at sea.”[233] Now, on June 19, having amply demonstrated that the Japanese could indeed be beaten at sea, Yi voiced his dissatisfaction one more time:

It seems to me that because national defense against enemy attack depended solely upon the army, defending weakly fortified city walls, instead of upon the navy fighting at sea, our fair land of many hundred years has become the enemy’s stamping-ground overnight. When I think of this tragedy I am choked with sadness and I cannot utter any more words. Should the enemy invade this province by sea, I shall go out to sea and defend it at the risk of my own life, but in the event of the enemy coming by land the generals without horses have no way to fight.

King Sonjo and his ministers rejoiced at Yi Sun-sin’s success in resisting the Japanese. But not everyone appreciated his candor. In pointing out the deficiencies in the government’s prewar defense policies, Yi was questioning the actions of powerful and influential men, men who could do him a great deal of harm.

It is not clear which Japanese units Yi Sun-sin met and annihilated in the Battles of Okpo, Happo, and Chokjinpo between June 15 and 17, 1592. Some sources assert that they belonged to Todo Takatora, but it is also possible that they were under the command of Mori Terumoto or Kobayakawa Takakage. One thing is certain, however: these enemy forces did not constitute the full might of the Japanese navy, such as it was. They were mainly transport vessels that were no match for the heavy Korean warships and their batteries of guns.

Hideyoshi had planned to provide his invasion force with strong naval protection. But his confident daimyo generals had not felt much need for it. They crossed over to Korea while the Japanese navy was still organizing itself at Nagoya and landed at Pusan without encountering any resistance at sea, thus confirming their assumption that the Korean navy could be disregarded. By the time Hideyoshi’s navy finally arrived at Pusan two weeks later, the vanguard contingents under Konishi, Kato, and Kuroda were already two-thirds of the way to Seoul, the entire southern half of Korea lay wide open for the taking, and the Korean navy, if indeed there was one, remained totally silent.

All of this heady success led the Japanese to become even more careless with regard to naval matters during the first few weeks of the war. When the main force of their navy finally reached Pusan on June 6, two weeks behind Konishi’s first contingent, it gave little thought to defending its beachheads and securing command of the sea to the west. It was largely taken for granted that Japanese ships would be able to sail unmolested along the southern coast and into the Yellow Sea, the route to advance bases to the north. Indeed, what was the point of keeping men on ships in harbors to the south, guarding against a non-existent seaborne threat, when there was so much work to be done inland? Several commanders of the Japanese navy thus left their ships and joined their army counterparts in the race up the peninsula. Wakizaka Yasuharu, for example, naval commander for the Tsushima theater, marched his crews north to defend a position near Yongin before eventually returning to his ships at Pusan. Naval commander Kurushima Michiyuki was ordered to prepare residences for Hideyoshi to use during his coming trip to Seoul, and so he too spent his first days in Korea somewhere inland, far from the ships he was supposed to command.

The squadrons that Yi Sun-sin had met and annihilated in June of 1592 were thus not the cream of the Japanese navy, if such can be said to have existed. They were disorganized bands of mainly transport ships that were probing westward with the intention of securing the Korean coastline between Pusan and the Yellow Sea, and doing a little looting along the way. They did not expect to encounter much resistance from the Koreans, certainly not in the form of formidable armored warships, and when they did they beat a hasty retreat.

The loss of more than forty of their ships awoke the Japanese to the fact that the Korean navy was not yet beaten. It was still not seen as posing a very great threat, however, for according to the reports brought back to Pusan the Koreans had fewer than fifty large and medium-sized ships. Still, the problem had to be dealt with. The southern coastline had to be secured so that Japanese ships could begin ferrying reinforcements and supplies north via the Yellow Sea to the advancing front. A second operation to stamp out resistance along the southern coast was therefore launched in early July. This time it would comprise not just transports. There would be warships under the command of such maritime daimyo as Kurushima Michiyuki, Kamei Korenori, and Wakizaka Yasuharu.


Cholla Left Navy Commander Yi Sun-sin spent nearly three weeks at his home port of Yosu following the Okpo campaign, resting his men, repairing his ships, and planning a second operation against the Japanese. The hiatus was finally broken when word arrived from Won Kyun, based farther east in Kyongsang Province, that Japanese naval forces were beginning to advance in earnest along the southern coast. They were already as far as Sachon, dangerously close to Commander Yi’s home port. Yi knew that Yosu could not stand against a land attack and that the only way to forestall the Japanese was to attack them at sea before they advanced any farther. Not waiting for the arrival of Yi Ok-ki’s Cholla Right fleet, Yi Sun-sin immediately sailed east on July 8 with just twenty-three warships. This time he discarded the small sea ear fishing boats—he had found them of minimal use during the previous campaign—but added something altogether more formidable: the kobukson, or turtle ship.

Yi and his master shipbuilder Na Tae-yong did not invent the kobukson as is often assumed. It had been developed some two centuries before, to combat the wako pirates then causing havoc along Korea’s coasts. Its first appears in the historical record in 1413, in a brief report in the annals of King Taejong of the monarch viewing a mock battle between a kobukson and a Japanese warship. The vessel by all accounts proved highly effective. Over the course of the next century and a half, however, the value of the kobukson seems to have been forgotten as Korea’s military preparedness waned, until it finally became just a dim memory preserved in history books.

It was this dim memory that Yi Sun-sin resurrected and refined. No contemporary account exists of exactly what the vessel he built looked like. Yi himself has left us only this vague description:

Previously, foreseeing the Japanese invasion, I had had a Turtle Ship specially built with a dragon’s head, from whose mouth we could fire our 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 cannon balls and fire-throwers.

Yi’s nephew, Yi Pun, who served under the commander during the latter part of the war, added a few more details in the biography of his uncle that he subsequently wrote:

He invented a warship of the same size as a board-roofed vessel [panokson]. On its upper deck were driven iron spikes to pierce the feet of any enemy fighters jumping on it. The only opening was a narrow passage in the shape of a cross on the surface for its crew to traverse freely. At the bow was a Dragon-head in whose mouth were the muzzles of guns, and another gun was at the stern. There were six gun ports each, port and starboard, on the lower decks. Since it was built in the shape of a big sea turtle, it was called Kobuk-son (Turtle Ship). When engaging the enemy wooden vessels in a battle, the upper deck was covered with straw mats to conceal the spikes. It rode the waves swiftly in all winds and its cannon balls and fire arrows sent destruction to the enemy targets as it darted at the front, leading our fleet to victory in all battles.

The description in Sonjo sujong sillok, the revised annals of King Sonjo compiled some fifty years after the war, is so similar to Yi Pun’s that it was likely based upon it.

These two passages contain virtually all the information we have of the turtle ship from individuals who actually saw one or heard of it firsthand. For more detail it is necessary to move forward to a description of the vessel written two hundred years later for inclusion in The Collected Works of Yi Sun-sin, compiled and published in 1795.

The editors of this work listed the sizes of the kobukson’s key timbers, the number of cabins, ports, and oars, and various other bits of information like the exact size of the dragon’s head adorning the bow. Adding this information to Yi Sun-sin’s and Yi Pun’s descriptions, the following picture of the turtle ship emerges. It was roughly twenty-eight meters long, nine meters wide, and six meters high from its flat, keeled bottom to the top of its roof. It was, in other words, a fairly large ship for its day, but sat quite low in the water, allowing it to come in under the high “castles” of Japanese fighting ships and blast away at their hulls near the waterline. A sloping roof of stout planks was laid on top of the bulwarks, totally encasing the vessel like the shell of a turtle, with just a narrow slit at the apex to allow a mast and sail to be raised and lowered. The roof was covered with iron spikes to disable enemy attackers if they attempted to board. The primary means of propulsion, particularly in battle, when speed and maneuverability were of prime importance, were twenty sculling oars, ten per side, each oar handled by two or three men. Cannons pointed out from loopholes on port and starboard, bow and stern, about fifteen guns in all. The interior of the vessel, finally, consisted of two decks: a lower propulsion deck for the oarsmen, and an upper fighting deck for archers launching regular and fire arrows and for gun crews manning chonja (heaven), chija (earth), hyonja (black), and hwangja (yellow) cannons mounted on wooden carriages.

Yi Pun’s assertion that straw mats were laid upon the roof to disguise the spikes might seem at first unlikely as this would have turned the kobukson into a floating tinderbox, ready to be set alight by the many fire arrows used in sea battles at that time. Keeping the mats soaked with seawater, however, would not only have solved this problem, but additionally would have made the roof fire retardant.

By far the biggest point of contention regarding the turtle ship is whether or not its spiked roof was covered with iron plates. Early English-language accounts of the Imjin War usually described it as such, typically adding that it was the world’s first ironclad ship. This latter claim is certainly not true. Fifteen years earlier in Japan, Oda Nobunaga had employed ships armored in some manner with iron against the fleet of the rival Mori clan in Osaka Bay, a technological innovation that the Japanese never capitalized on. Indeed, it is unlikely that Yi Sun-sin’s turtle ship was iron plated at all. The evidence to support this claim does not exist. An ironclad ship would have been something new in Korea in the late sixteenth century and would certainly have excited comment somewhere in the many letters and diaries and reports that survive from this period. Yet Yi himself makes no mention in either his diary or his reports to court of any sort of iron plating covering the roof of his kobukson. Nor does his nephew Yi Pun in his biography of the admiral. Nor does Korean prime minister Yu Song-nyong in his own account of the war. (Yu describes the kobukson as “Covered by wooden planks on top.”) Nor do the annals of King Sonjo, that exhaustive compilation of dispatches, reports, conversations, and comments from this period running into the many thousands of pages. In fact, no mention exists in any contemporary Korean account of the war that the turtle ship was ironclad.

Another factor weighing against iron plating is the difficulty that Yi Sun-sin would have faced in acquiring enough metal to cover even one large ship, let alone several. In his treatise in support of the iron plating theory, Bak Hae-ill, extrapolating from the iron cladding on the doors of Seoul’s fifteenth-century Namdaemun Gate, estimates that six tons of metal would have been needed to cover the roof of one turtle ship with plates two to three millimeters thick. That is a lot of iron, the equivalent of the vessel’s entire complement of cannons. Considering that Yi Sun-sin received so little support from the government and had to scrounge most of the materials he needed to repair and outfit his fleet, the acquisition and use of such a load of iron would have been difficult, and probably would have been considered more usefully employed in the casting of additional cannons, enough to outfit an entire new ship. Yi himself considered it worth mentioning in his diary the relatively insignificant amount of fifty pounds of iron that he sent to Cholla Right Navy Commander Yi Ok-ki as a gift in early 1592. And yet nowhere does he mention acquiring and using six tons of the metal—that’s twelve thousand pounds—to cover his turtle ship.

Such a lack of evidence cannot rule out completely the possibility that the turtle ship had some sort of iron plating on its roof. But it does seem to weigh heavily against it. Until further information comes to light to the contrary, the likeliest conclusion is that Yi Sun-sin’s turtle ship was armored only insofar as it was constructed of heavy timbers and covered with a thick plank roof studded with iron spikes—which against the light guns of the Japanese was armor enough.

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