(28) King Sejong: Pioneer of Gunpowder Weapons

By Yang Sung-jin

Not long after its foundation in 1392, the Choson government had to stave off sporadic attacks from the Jurchen Manchus on its northern borders. Though the Jurchen’s military prowess was relatively inferior, the nomadic tribe displayed threatening cavalry tactics, often catching the Choson frontier soldiers off guard.

To tame the hit-and-run Jurchen, Choson defense officials were in need of long-range weapons. Archery was a decent option as arrows had a maximum target range of around 360 meters. Yet it was impossible to mass produce bows because the basic material needed (water buffalo horns) was covertly imported from China, and thereby critically limited in supply. Worse, it took a considerable amount of time to train a skilled archer.

For this reason, gunpowder weapons were more than a blessing for the Choson defense ministry. They had a considerably longer attack range, their destructive capabilities were awe-inspiring and the necessary training period was brief.

In the earlier reign of King Taejong (r. 1400-1418), gunpowder weapons were too heavy to be managed by individual soldiers, so they were mainly mounted on battleships in a bid to attack invaders at sea. Years later, the continued upgrading of primitive gunpowder-based arms made it possible for them to be used for ground battles.

In the latter years of King Taejong’s reign, a 10,000-strong special gunpowder unit was put into active operation, hinting at a wider use of explosives in the military sector.

It was King Sejong (r. 1418-1450) who brought in the great advancements in gunpowder weapons. The fourth monarch of the Choson Dynasty introduced a set of standard rules which regulated the manufacturing of gunpowder-related firearms.

Today’s historians are of the opinion that King Sejong’s endeavors laid the foundation for the Choson’s ability to break free from China’s influence and forge independent advances in the development of gunpowder weapons.

Understandably, the King Sejong volume of the Annals of the Choson Dynasty contains numerous articles on the subjects of gunpowder and firearms.

King Sejong: Gunpowder Innovator

According to an article dated Jan. 22, 1425, a Cholla province governor developed a new breed of cannonball for gunpowder cannons and brought to King Sejong a total of 3,308 projectiles.

In October of 1431, the Ministry of Military Affairs reported, “Since the ministry’s firearms storehouse is situated among private houses, a fire has the potential to break out. Therefore, it should be relocated to a compound far away from the residential area.” Immediately, King Sejong granted the relocation to protect innocent citizens.

In 1444, Lee Chon, a high-ranking official in the field of military arsenal procurement, called on King Sejong to acquire advanced weapons technology from the Jurchen, otherwise known as “Yain.” He said, “Since we cannot get any lead and copper here, we have been experimenting with cast iron in cannon manufacturing, which is highly difficult. The northern Yain tribe are said to know how to handle soft iron and so we should learn from them.”

At that time, Choson blacksmiths used cast iron to produce farm appliances. Yet cast iron was inappropriate for weapons-making because it was too rigid and easily breakable. The material had to undergo a softening process to make it suitable as a raw material for weapons. The final soft iron was duly precious since it was only a quarter of the original cast iron in size after the softening process.

Meanwhile, the high value of soft iron fanned illegal smuggling. In 1433, the Ministry of Military Affairs called for the strengthening of punishments on those who covertly sold soft iron to the Japanese.

In 1445, King Sejong launched a large-scale project to upgrade cannons and other firearms which devoured a huge quantity of gunpowder, and yet were inefficient, with a conventional target range of only 900 meters.

On March 30 of that year, King Sejong addressed the Uijongbu (State Council): “King Taejong (the monarch who handed over the throne to King Sejong) approached me and said that firearms are important for the national defense. He also suggested the appointment of Yu Eun-ji to take charge of the development of cannons, which I approved.”

The project, however, produced little improvement. Undaunted, official Yu secured and studied Chinese cannons, whose level of technology was far advanced than Choson’s. Finally, he succeeded in developing cannons of high caliber with target range of over 2,340 meters. Moreover, new firearms capable of discharging four arrows at a time were developed.

Blacksmith’s Shop Near Palace

King Sejong’s unusual interest was the trigger for the successful development. To upgrade the cannons, King Sejong often gave lectures to court officials about firearms, refurbished related laws and even ordered a blacksmith’s shop to be built near the royal palace to supervise the research as often as possible.

Interestingly, the appointment of Yu Eun-ji as chief of the project, which later proved successful, was largely due to King Sejong’s somewhat dogged insistence on protecting talented manpower by all means.

Yu was a career diplomat and often dispatched to China. But he faced a critical moment in 1436 when his daughter became the subject of a sex scandal, a heinous breach of Confucian principles.

Despite the high-pitched appeals calling for his dismissal from the office, King Sejong stood behind Yu, saying that his daughter’s crime should not disadvantage Yu.

King Sejong’s aspiring project hit a snag in June of 1445 when the reserves of iron and lead for firearms manufacturing dried up. That there was no lead mine in the Korean peninsula made the situation worse. To tackle the shortage, the king desperately ordered each province governor to make sure that each and every dish made of lead was registered — including those belonging to Buddhist temples.

The following month, the king declared a new ordinance that awarded those who helped produce the precious lead: “Lead and iron are important for our defense and yet their quantity is now far from sufficient. In addition, we lack technicians capable of refining lead properly. From now on, those who find a vein of lead or provide a tip for lead-refining will be awarded.”

In 1446, King Sejong ordered that all the officials involved with gunpowder and firearms should be registered with the government supervision even after retirement. The measure at once put competent technicians on standby for a possible emergency and blocked the outflow of important defense technology.

When “Chongtongtungrok,” a book detailing the manufacturing secrets of advanced cannons was published in 1448, King Sejong said, “This book contains the methods of producing cannons and handling gunpowder in detail. To keep the secret, the book should be preserved in a hidden place and unauthorized readings should be tightly controlled, as well.”

Unfortunately, the confidential gunpowder technology was divulged outside of the palace in the late 15th century. And the price of the carelessness was dearer than ever; in the mid-16th century, the classified information ended up in the hands of “waegu,” or the seaborne Japanese marauders, which led to more destructive pillaging on the Choson coast in the years that followed.