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    While Yi Manchu and Mentemu were engaged in a bloody battle of cat and mouse in the north, operations targeting Tsushima and the Nine Provinces were steadily progressing in the south.

    As Sejong personally oversaw matters in the north from the Hamheung temporary palace, Hyang took charge of the southern front from Eastern Palace in Gyeongbokgung Palace.

    “The operations against Tsushima and the Nine Provinces must never stop.”

    “However, most of our military strength is currently focused on the north, and a significant portion of our finances has been consumed by war expenditures, with uncertainty about how much more will be spent. Might it be wise to postpone our plans?”

    As Kim Jeom argued for a delay, Jo Mal-saeng immediately objected.

    “Absolutely not! The Japanese merchants near trading posts are aware of the unfolding war in the north. They will meticulously gauge the extent of Joseon’s capabilities! If we show weakness now, the Japanese pirates may wreak havoc once again!”

    Hyang nodded gravely at Jo Mal-saeng’s words.

    “It’s a possibility.”

    “But all our challenger-class warships have been deployed to the north!”

    Kim Jeom remained skeptical, citing the absence of their challenger-class vessels.

    Although few in number, the challenger-class warships had become the backbone of the Joseon Navy. They boasted far superior firepower, transport capacity, and operational endurance compared to the existing panokseon and other vessels.

    In response to Kim Jeom’s remark, Jo Mal-saeng countered again.

    “Wasn’t it already decided that the panokseon would take over their duties? Why do you keep mentioning the challenger-class warships? Are you genuinely concerned, or are you opposing for the sake of opposition?”

    At Jo Mal-saeng’s pointed question, Kim Jeom raised his voice.

    “It’s because of our finances! Our finances!”


    Hyang interjected, having observed their heated exchange.

    “I understand the Finance Minister’s concerns, but in this case, I believe it would be wise to proceed as the Minister of Defense suggests. Now that the eyes and ears of Japan are fixated on us, we must display confidence, even if it’s a mere show of force. Although it may be akin to ‘pissing with a morning erection,’ we shall allocate funds from the Insubu, the Crown Prince’s personal treasury, if necessary.”

    With Hyang’s strong push, Kim Jeom fell silent.

    Thus, the series of policies targeting Japan were able to continue unimpeded.


    Tsushima was the first to undergo the operation.

    Joseon first dispatched an envoy to the Lord of Tsushima.

    “As promised, we will begin constructing our base in Asō Bay.”


    “We look forward to your cooperation.”

    After informing the Lord of Tsushima about the base construction, Joseon promptly transported laborers and materials to commence the project.

    The first areas where Joseon broke ground were Mizusaki and Toyotama.

    “Ideally, we would transform this entire Asō Bay region into a Joseon naval base in one fell swoop, but that would make Lord So of Tsushima exceedingly wary. Let us gradually encroach upon it instead.”

    “Yes, sir.”

    “Where should we begin first?”

    “The Mizusaki and Toyotama areas seem suitable. They are not too deep into the island, and there is ample space to establish a naval station.”

    “Then let us proceed accordingly.”

    Following Hyang’s decision, a fleet of panokseon laden with vast quantities of materials and a large contingent of laborers entered Asō Bay.

    News of Joseon’s movements in Asō Bay reached the Lord of Tsushima almost in real-time.

    “Mizusaki and Toyotama…”

    Upon receiving the report, So Sadamori, the Lord of Tsushima, stroked his beard as he examined a map. His retainers, who were studying the map alongside him, began to speak one by one.

    “They have an eye for strategic locations.”

    “Indeed, my lord. Those areas provide easy access to the outer sea.”

    As Sadamori listened to his retainers’ explanations while observing the map, he lifted his head and glared at them.

    “What about their approach to Izuhara?”

    The retainers promptly responded after re-examining the map.

    “The terrain is most unfavorable.”

    “If they come by ship, they will have to circumnavigate the island, making their approach visible. If they come by land, they must cross Asō Bay and then traverse the mountains, which is not ideal.”

    At the end of his retainers’ responses, Hatoyama, the most senior among them, pointed to a specific location on the map and spoke.

    “The only concerning factor is Komoda. They could land troops there and then advance. Therefore, it would be wise to construct a mountain fortress at Shimobaru to block that route.”

    Sadamori nodded at Hatoyama’s suggestion.

    “That would be best. Make it so.”

    “Yes, my lord!”

    Having issued his orders, Sadamori reminded his retainers once more.

    “Although Joseon speaks of peace now, we must never trust them.”

    “Yes, my lord!”

    Following the turbulent period of the late Goryeo Dynasty, when the Japanese pirates invaded Joseon, and the Tsushima conquest led by Yi Jong-mu[1] in the first year of Sejong’s reign, Joseon and Tsushima harbored mutual distrust.


    As Joseon and Tsushima maintained their vigilance, the Joseon military began constructing the naval station.

    The first task undertaken by the Joseon forces was to build a mountain fortress surrounding Mizusaki and Toyotama.

    A mountain fortress with a radius of approximately 300 jang (990 meters), centered on Mizusaki, began to take shape along the ridgeline encircling Mizusaki and Toyotama.

    Naturally, this process did not escape the watchful eyes of the scouts dispatched by the Lord of Tsushima.

    Upon receiving reports from his scouts, Sadamori could not conceal his bewilderment.

    “They are constructing a mountain fortress first? What are they thinking? Building a mountain fortress is no simple feat!”

    Sadamori’s retainers nodded in agreement, wearing similar expressions.

    Joseon-style mountain fortresses were not unfamiliar to Sadamori and the people of Tsushima.

    Through their interactions with Goryeo and later Joseon, Sadamori and the Japanese had gained some knowledge of Joseon-style mountain fortresses. Moreover, an actual example of a Korean-style mountain fortress called Kanataki existed atop Mount Kurosei in Mitsushima.

    As a result, following the Tsushima conquest, Sadamori and his retainers had built Joseon-style mountain fortresses at key defensive points. During that process, they had come to understand that constructing a Joseon-style mountain fortress was no easy task, leading to their current puzzlement over the Joseon Navy’s actions.

    “Wouldn’t it be logical to first establish a dock and then build defensive structures?”

    “Indeed. I cannot fathom what the Joseon military is scheming.”

    Unable to find an answer despite their contemplation, Sadamori had no choice but to issue a fundamental order.

    “Send more scouts.”

    “Yes, my lord!”

    The additionally deployed scouts continued to report on the movements of the Joseon forces.

    As the scouts’ reports poured in, Sadamori grew increasingly perplexed.

    “They are dredging sand?”

    “Yes, my lord!”

    The Joseon military was not only extracting sand from the rivers flowing into Mizusaki but also haphazardly excavating sand from the nearby white sandy beaches.

    Upon receiving the report, Sadamori’s head began to ache.

    “I have no idea what they are up to.”


    While Sadamori writhed in frustration, unable to solve the mystery, the Joseon forces were busily at work.

    “The mountain fortress will be built from here to there.”

    An official from the Construction Department, who had accompanied the navy, examined the map and turned his head to survey the ridgeline where the fortress would be built. After roughly estimating the scale with his eyes, the official soon spoke.

    “We will need a lot of sand. As soon as the water-lifting machines arrive, we must begin work.”

    “The water-lifting machines will arrive with the next shipment in three days.”

    “Then we should inspect the actual site where the mountain fortress will be constructed.”

    As the official rose from his chair, Kim Gyeong-sik, the commander of the Tsushima garrison, added.

    “I will assign an escort for you.”

    “Thank you.”

    Three days later, with the arrival of the water-lifting machines, laborers, and materials, the work began in earnest.

    “Start by dredging the sand accumulated in the rivers first.”

    “Yes, sir.”

    Following the official’s orders, the foremen led the laborers to commence work.

    While one group of laborers scooped sand from the rivers and transported it, another group began digging along the ridgeline.

    Soon, combat engineers dispatched from Joseon arrived, accelerating the pace of the work.

    As trenches of considerable depth were dug, resembling defensive trenches, a large quantity of steel reinforcement bars was transported.

    Upon the arrival of the steel bars, skilled workers wove them together using wire. Once the steel bars were properly positioned, wooden molds coated with pitch were used to create formwork.

    After the entire process was completed, well-mixed concrete was poured into the formwork.

    Five days later, when the wooden molds used for the formwork were removed, sturdy fortress walls were revealed.

    Naturally, the sand dredged from the rivers alone could not meet the required volume.

    Therefore, the laborers began extracting sand from the white sandy beaches.

    During this process, the water-lifting machines brought along played a crucial role.


    As the steam engines moved with a loud roar, freshwater from the rivers was sprinkled over the sea sand piled up in the filtration area.

    After being rinsed with freshwater for several days to remove the salt, the sand was promptly loaded onto carts and transported to the construction site. Upon the sand’s arrival, the laborers in charge of mixing combined the sand, gravel, slaked lime, and water in a mixer and began the mixing process.

    The properly mixed concrete was then poured into large containers and loaded onto carts using a crane. When the carts arrived at the formwork location, sturdy steel pulleys lifted the containers above the formwork, and the workers poured the concrete into the formwork.

    Both the crane and pulleys were Hyang’s creations. The ministers, who had doubted the utility of the crane and pulleys, applauded enthusiastically when they witnessed their remarkable performance at the reconstruction sites of Bukhansan Fortress and Namhansan Fortress.

    “We must immediately distribute these to all construction sites across the country!”

    As the ministers chorused in unison, Sejong glanced sideways at Hyang and muttered.

    “Indeed… I should seize him and shake him down thoroughly someday… He only releases bits and pieces when he needs something…”

    Unaware of Sejong’s thoughts, Hyang grumbled to himself.

    “Once the miniaturization and high-output of the steam engine are achieved, I must immediately create a power crane. A single scoop would suffice…”


    After two months, a mountain fortress made of sturdy stone walls following the ridgeline was revealed.


    Upon receiving the report, Sadamori jumped up from his seat.

    Sadamori and his retainers left Izuhara and visited the Joseon military garrison.


    “Thank you for the warm welcome. I should have visited sooner, but I was delayed due to pressing matters.”

    “Not at all…”

    After a formal exchange of greetings, Sadamori broached the main topic.

    “I heard that a mountain fortress was completed in a short time since the arrival of the Joseon Navy. It is truly remarkable.”

    In response to Sadamori’s remark, Commander Kim Gyeong-sik replied nonchalantly.

    “It was a small mountain fortress, so the work progressed quickly.”

    “Constructing a fortress is no easy feat, is it not?”

    “Everything becomes easy with determination and a clear path.”

    “May I take a brief tour of it?”

    “By all means.”

    With a frank response, Commander Kim personally guided Sadamori to show him the fortress walls.

    ‘How can this be!’

    Upon examining the walls, Sadamori was rendered speechless. Although they were clearly made of stone, there were no visible seams.

    Returning with a deflated expression, Sadamori stammered as he shared his impression with Commander Kim.

    “It is truly astonishing.”

    “This is merely ordinary. In Joseon, there are numerous fortresses larger and sturdier than this one.”

    “Is that so?”


    On the way back to Izuhara, Sadamori muttered, still wearing a dumbfounded expression.

    “How on earth… Is such a thing truly possible?”


    Footnote 1: Joseon-style mountain fortress on Tsushima. Lee Deok-il. The Chosun Ilbo. July 22, 2008.


    1. was a Korean general who led the Oei Invasion of Tsushima Island in 1419[]

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