Chapter 102: Asiatic Northern War Part II - Struggles for the Straits and Tsushima
Despite Joseon not having engaged in any naval conflict since its punitive expedition against the Sou clan in 1419, the peninsular kingdom possessed an impressive navy. As Joseon began to engage in trade with the outside world in the 17th century, attention was given to its coastal and maritime defenses. Both the increasing power of Japan and the perceived threat of European ambitions incentivized technological advancements in Joseon ship design. The base designs of the panokseon and bangpaseon, which already exceeded the Japanese tekkousen in utility and firepower, was modified to incorporate innovations inspired by the warship designs of the English and Dutch merchants that Joseon interacted with. Joseon would also build warships based on European designs in their own shipyards, albeit to a lesser extent than the Japanese. Because of this, Joseon’s main disadvantage on the seas would not be technological in nature but rather numerical, as the Japanese navy was significantly larger. Therefore, Gyeongseon hoped to quickly blockade the Tsushima Straits and occupy the key islands of Tsushima, Okishima (沖島), and Iki, defeating any nearby large fleets before the Japanese could bring together its entire naval might as its various squadrons were spread across the realm. Then, the navy could proceed to cut off Japan from the mainland entirely, assuring the final defeat of the Amur Khanate and its Japanese reinforcements.
Modern day 3D model of a 17th century panokseon
Using this outline of a strategy to guide his actions, admiral Byeon Ge-up immediately activated the Joseon navy and began swarming the Tsushima Straits. A portion of the navy would commence an invasion of Tsushima while the main detachment would sail towards the Kanmon Straits to initiate a blockade and prevent the various Japanese navies from uniting into one force. Learning of Byeon Ge-up’s approach, Mōri Tsugumoto and Kobayakawa Motokane (小早川元包) mobilized the Mōri clan’s own navy and alerted Seikou’s senior deputy, Kanamori Shigekazu (金森重一) as the naval shogun was in Bireitō when the Joseon navy had been activated. Shigemasa would mobilize the fleets in Hyogo and Sakai to back up the Mōri and prevent Joseon from blockading the Kanmon Straits and controlling Japan’s most important trade route. By the spring of 1667, the various naval forces had coalesced to confront Byeon Ge-up himself with a total force of 40 ships. Furthermore, Shimonoseki’s defenses were strengthened, its garrison reinforced. Meanwhile, Ge-up amassed a slightly larger fleet of 45 ships upon hearing reports of the impending Japanese response and geared up for a full-scale naval confrontation.
On May 10th, the Battle of Umashima (馬島の戦い) occurred, taking place just off the island of Umashima (馬島) which was situated in front of the straits’ western end. On the Japanese side, Kanamori Shigemasa commanded the larger Azuchi contingent while Kobayakawa Motokane led the smaller Mōri navy, which was positioned in the front as the Mōri were the most familiar with Joseon’s military. Motokane put the Mōri clan’s zentousen just behind the front line of hobayasen, carracks, and galleons, hoping to replicate the same strategy behind the Japanese victory at Pasaleng Bay in the Iberian-Japanese War. To the northwest the Joseon navy, with Byeon Ge-up commanding from the back and his deputy Yun Si-min manning the front. The panokseons were concentrated in the front as they were the most nimble vessels in the Joseon navy and therefore perfect for navigating the narrower currents of the area. The battle began as soon as the sun shone as the Mōri contingent immediately began advancing. Yun Si-min, however, held back his panokseon vessels until the Japanese had closed much of the distance before moving an initial forward advance. Although under heavy fire, the panokseon’s maneuverability allowed them to dodge many cannonballs, and the ships that made it through fired at close range and managed to board several Japanese vessels. Intense fighting ensued, with both sides inflicting heavy casualties. However, the thicker armor of Joseon’s sailors overcame the greater agility of the Japanese sailors. Seeing the close combat taking place, Shigemasa ordered galleons and carracks on the wings to flank the Joseon panokseons and break the stalemate, quickly followed up by Byeon Ge-up’s own heavier junks and galleons that backed up the panokseons. After hours of naval warfare, seeing a breakthrough to be either impossible or too costly, Byeon Ge-up decided upon a retreat and ceding the entirety of the straits back to the Japanese. However, the Japanese had lost more vessels, making the battle a draw. Although Joseon had been unsuccessful in taking the straits, they had more than proven their might.
Blue = Joseon, Salmon = Japan
The Battle of Umashima also blocked the Japanese from sailing through the straits and breaking Joseon’s naval encirclement of Tsushima. Tsushima was ruled and guarded by Sou Yoshizane (宗義真) and his retinue of 1,500 and would be heavily outnumbered and outgunned by the Joseon navy and its transported land forces. Nevertheless, Tsushima was a heavily fortified island and its samurai were ready to fight for every last bit of it. Gim Jeong-il, a vice admiral, would supervise the encirclement and assault of the island. Joseon’s ships began to be reported as early as March 1667 from the island but the assault wouldn’t officially begin until April 13th. The paltry navy of the Sou clan was quickly destroyed, and a sizable Joseon force soon landed on the northern side of the island, quickly occupying it. However, the south was populated with numerous castles and fortifications and would prove to be a challenge for Jeong-il’s men. Initially, another force landed in the far south with little resistance, only to soon be inflicted with ambushes by small bands of samurai and armed farmers and fishermen. They were then defeated in battle by an army led by Sou Yoshizane himself in the southern vicinity of Kaneishi Castle (金石城), the main castle of the Sou clan. Meanwhile, Joseon’s advance from the north was halted when the Sou clan torched the bridge spanning the Kusubo Channel (久須保水道) that divided the northern and southern sides of Tsushima. Although the Joseon navy had supported its land counterparts through supply drops and bombardments of key Sou positions, notably reducing Kaneda Castle (金田城) to smoldering ruins, they were unable to cow Tsushima’s most important fortifications into submission through a mix of the enemy’s resolve and counterfire. The assault had expected to succeed within a month but Sou Yoshizane and the island’s defenders still stood defiant in the aftermath of the Battle of the Kanmon Straits. Because of this, Gim Jeong-il would make preparations to bring more men against the Japanese beyond the 10,000 that were already fighting Yoshizane.
Blue = Joseon, Salmon = Japan
During this time, preparations were being made to break Joseon’s constriction of Tsushima and prevent future attempts at seizing and blockading the Kanmon Straits. In Kyushu, Shimazu Norihisa was busy gathering a force of 10,000 from amongst the daimyo on the island to protect the Kyushu end of the straits. Meanwhile, Tagawa Seikou sailed to Nagasaki at the head of a navy composed of his personal junks and the Iriebashi squadron, with more ships to be contributed by the Shimazu, Horiuchi, and Ryuzōji clans. He chose to leave a naval presence near Luson province to continually protect Japan’s mercantile interests in the South China Sea and beyond and discourage Spain, Siam, or even the VOC from taking advantage of Azuchi’s preoccupation with matters against the Lesser Jin and Joseon. Nanbu Naofusa (南部直房), who commanded the Hakodate naval squadron within Japan’s navy, was also busy against the Joseon navy, engaging in naval skirmish after skirmish in the hopes of freeing up the seas between Kanazawa and the mainland so that the rest of Kaga Nagaaki’s expeditionary force could safely cross over and coalesce with Sakuma Moritora’s and Sassa Katsutoyo’s armies as well as Bahai Khan’s Amur Jurchen horde.
Unexpectedly, the waters between Japan and Joseon had become the main battleground of the Asiatic Northern War, originally expected to be limited in scope beyond the northern steppes of the Jurchen people. The naval warfare would continue for the rest of the year and it would have a significant effect on the war and the welfare of the involved realms. In particular, the naval escalation would begin to disrupt the trade routes flowing from both realms as the waters became more dangerous for native and foreign merchants alike. This would prove to be its own variable within the context of the war and wider regional affairs.