(continued)
While diplomatic wrangling continued between Seoul and Kyoto, Admiral Yi was busy creating a genuinely secret weapon, the kobukson, or "turtle ship" (Figure 1). Although Yi Sun-sin is commonly given credit for inventing the "turtle ship," the term kobukson was actually used in historic documents as early as 1414, when King T'aejong first inspected this new warship design. The aggressive use of the kobukson in Koryo's 1419 raid against pirates on Tsushima Island certainly indicates it was originally designed as an attack ship.
Beginning with a hull design adapted for high speed and maneuverability, Admiral Yi's highly-modified kobukson was essentially a flat-bottomed, oar-powered galley 100 feet in length with a 25 foot beam and two large masts rigged with large rectangular sails. Admiral Yi did not have to defend the open seas of the Tsushima Strait, but faced the constant battlefield constraint of inadequate maneuvering room in the narrow channels and shallow waters among the 400 small islands and uninhabited islets of the Hallyo Waterway. This small inland sea stretches 172 km from Hansan Island in the east, including Ch'ungmu, Samch'onp'o and Namhae Island, Odong Island, to the seaport of Yosu in the west.
Japanese superiority in both soldiers and firearms made engaging Japanese ships at close quarters a very dangerous tactic. Admiral Yi could not afford to be boarded, so he designed an arched "roof," believed to have been made of iron plate, that covered ship's entire topside structure to ward off enemy arrows and cannon shells. The top of this roof was studded with sharp upright spikes to deter potential boarders. The Yi court had discussed the idea of building ironclad ships as early as 1413, but the world's first ironclad warship was not actually built until Yi Sun-sin took command of the Choson navy.
Choson had already manufactured some very powerful cannons designed to protect fortresses and they soon figured out how to put them on ships. Yi Sun-sin increased the firepower of his kobukson by mounting thirteen small cannon atop the rowing deck along both flanks of the ship that fired through portholes to allow the vessel to deliver a broadside attack from either side at will. The Choson Navy had four types of cannons; ch'on (heaven), chi (earth), hyon (black) and hwang (yellow). The heavy 660 pound ch'on cannon, with a 5.5 inch bore, could hurl a cannonball only a few hundred yards. Smaller and shorter in range than contemporary English cannons, Admiral Yi's guns certainly proved adequate to counter the threat posed by the smaller cannons aboard Japanese ships.
A large dragon head sat above the reinforced ram in the ship's bow and a wood-fired smoke generator was used to spew sulfur smoke through the dragon's grinning mouth. When put to use with the ship underway, the smoke screen enshrouded the entire ship and no doubt intimidated superstitious enemy sailors. The addition of new advanced cannons, archery ports ahead, astern and abeam, iron spikes on the roof, and the smoke generator in the bow made the kobukson a true offensive weapon.
The primary strength of Choson's professional military resided in its naval forces garrisoned along the southern coast, the direct result of Japanese pirate activity in Korea during the fourteenth century. In 1591, faced with an imposing threat from Japan and with Choson's very existence at stake, Chief Minister Yu Songnyong persuaded the royal court to appoint Admiral Yi Sun-sin to the post of Naval Commander of the Left (western) Cholla Province Naval Station headquartered at the southeastern port city of Yosu. There, in early 1592, Admiral Yi energetically set about training crews for his new warships.
With Choson enmeshed in factional squabbling, Hideyoshi readied his forces to move into Choson. From his headquarters in Hizen, Hideyoshi mobilized seven fully-equipped divisions, nearly 150,000 men and gathered a fleet of some 700 ships, transport vessels, naval ships and small craft to move his army across the Tsushima Strait. Many of the approximately 9,000 seamen who manned the Hideyoshi's fleet were reportedly former pirates. From their advanced staging area on Tsushima Island, an expeditionary force of three divisions (51,000 men) sailed for the south Choson coast near the end of May 1592 (Figure 2): 11,000 men under General Kuroda Nagamasa, 18,000 men under the leadership of General Konishi Yukinaga, a Christian born of a merchant family from Sakai, and 22,000 men commanded by General Kato Kiyomasa, a Buddhist "mustang" officer who rose from the ranks with Hideyoshi.
Pusan garrison troops under the command of Chong Pal manned beachhead defensive positions around Pusan To the north, a few miles inland at the small town of Tongnae, town magistrate Song Sang-hyon commanded a small civil defense force. General Konishi reached the port of Pusan a full five days ahead of generals Kato and Kuroda.The Japanese surprised and quickly overwhelmed the badly outnumbered defenders in both Pusan and Tongnae. Despite bravely defending the beachhead areas to the death, Choson's garrison troops proved no match for Japanese soldiers armed with short-range brass cannon and matchlock muskets. Moreover, they faced an army with extensive combat experience, men already bloodied from the many campaigns of Japan's Warring States period.
General Konishi had already established a beachhead in Choson by the time Kato and Kuroda's two remaining divisions reached Pusan (Figure 3). The combined Japanese army was too large to advance along a single route, particularly since the troops would have to live off the land. The Japanese left Pusan in three separate columns, opening a three-pronged northward assault toward the capital in Seoul. By messenger and beacon fires, reports of the invasion quickly reached the Yi court in Seoul along with reports of the many towns captured by the Japanese. Stunned by the news, King Sonjo's government panicked. The Border Defense Command quickly issued orders to call up the scattered remnants of the Choson army.
The government placed its hopes on the talents of General Sin Ip, a tough military fighter who had won earlier fame in successful campaigns against the Jurchen in the northern provinces. General Sin received orders to take all the men he could muster and contain the Japanese in the Naktong River basin by blocking the three mountain passes leading out of Kyongsang Province. Sin mustered a few thousand untrained men armed only with spears, bows and arrows. The leadership of this ragged group was even worse than the condition of the troops. Well before his small force reached the first of the mountain passes, General Sin received disturbing, detailed reports describing the Japanese army's battle prowess. Instead of taking the high ground, where tens of men could defend against thousands, the doughty general decided to wait for the advancing Japanese behind a strong defensive position established on an open plain near the city of Ch'ungju, where he felt his men would fight better than in the mountains.
General Kuroda's division swept westward through the Sobaek Range over the Ch'up'ungyong Pass and proceeded north through the western provinces toward Seoul. General Konishi's division moved virtually unopposed up the center of Kyongsang Province. Meanwhile, General Kato's division, the third prong of the Japanese assault, drove north from Pusan toward Kyongju, turned northwestward, then linked up with Konishi in the valley near Ch'ungju. After crossing the undefended Oryong Pass, Konishi's soldiers moved into the lower Han River valley, where the Japanese met their first strong resistance from General Sin Ip's rag-tag army. In the bitter and bloody fight that ensued, Japanese troops overran the Ch'ungju defenders and killed General Sin. The two Japanese divisions continued their march toward Seoul along two different routes. The main objective of the assault on Korea was plunder. The Japanese deployed six special units with orders to steal books, maps, paintings, craftsmen (especially potters) and their handicrafts, people to be enslaved, precious metals, national treasures, and domestic animals. Meeting little resistance, the Japanese ravaged the civilian population. Entire villages were swept up in the raids. Japanese merchants sold some to Portuguese merchants anchored offshore and took the rest to Japan.
If the summer of 1592 exposed fatal weaknesses in the Choson army with brutal thoroughness, it also highlighted the Choson navy's reputation. Admiral Yi Sun-sin proudly launched his kobukson in May 1592, just days before General Konishi's troops landed at Pusan. The admiral selected eight of his most courageous naval officers to act as commandants at various ports. He also called up four government officials from their posts as magistrates of local cities and put them in the forefront of his battle formations as commanders of the Left Wing, Front Forward, Central Forward, and Right Forward commands. Within days of the outbreak of the Imjin War, Admiral Yi Sun-sin sailed into the Hallyo Waterway in search of Japanese shipping intent on engaging and destroying it whenever and wherever it might appear.
The war was less than ten days old when the Choson Navy had its first major engagement against the Japanese. Sailing from the southwest early one morning, Admiral Yi sighted the supply and troop ships that landed two Japanese divisions near Pusan less than two weeks earlier lying at anchor near Okp'o, off Koje Island. Borrowing a maxim from Sun Tzu's Art of War - "If the soldiers are committed to fight to the death they will live, whereas if they seek to stay alive they will die." - Admiral Yi gathered his captains and repeatedly had them pledge their willingness to fight.
