㉙ Comparing the Weapons of Joseon and Japan in the Imjin War

In an earlier post, "① Not the Song of the Sword, but the Song of the Bow," I compared the Joseon bow with the Japanese matchlock and said that Admiral Yi's tactics came down, in the end, to long-range naval gunnery. This time I want to talk about the real protagonist of that long-range gunnery: the cannon carried aboard the panokseon, the main Joseon warship. The Cheonja, Jija, Hyeonja, and Hwangja cannons, the pyeonjeon arrow, and the bigyeokjincheonroe exploding shell: I will go through the range of each weapon the Joseon navy had, one by one.

The historical records give range in a unit called the bo (步, "pace"). But it is a mistake to think of a bo as a single step of one foot. One bo counted the whole motion of the right foot and the left foot each stepping forward once. It is the same idea as the Roman passus (double step).
According to the Korea Research Institute of Standards and Science (KRISS), Joseon used a ruler called the jucheok (周尺) and counted 6 cheok (feet) as 1 bo, and one jucheok foot was about 20 cm. That makes 1 bo about 1.2 m. Since one adult step is roughly 60 cm, a distance of about 1.2 m for one step of the right foot and one of the left fits the calculation as well.
In this post, I give figures converted on this basis (1 bo ≈ 1.2 m) in parentheses. Different sources use slightly different conversion values, though, so please treat them as reference figures.

Joseon Cannon: The Cheonja, Jija, Hyeonja, and Hwangja Cannons

Ever since Choe Mu-seon set up the Office of Gunpowder Weapons at the end of the Goryeo dynasty and began making gunpowder weapons, Joseon greatly advanced its cannon technology from the reign of King Sejong onward. It even recorded the methods of making and using them separately in a book called the Chongtong Deungnok (Register of Firearms). Each cannon was named, in order of size, after the first four characters of the Thousand Character Classic: cheon, ji, hyeon, hwang. The cannons were improved several times afterward, through the reigns of King Myeongjong and King Seonjo.

Cannon	Main projectile	Range (as recorded)	Converted (about 1.2 m/bo)	Notes
Cheonja cannon	Daejanggunjeon (about 2.4 m long, about 30 kg)	1,200–1,300 bo	about 1.44–1.56 km	The largest Joseon cannon
Jija cannon	Janggunjeon	800 bo	about 960 m	Second largest after the Cheonja
Hyeonja cannon	Chadaejeon / Chajungjeon	800 bo / 1,500 bo	about 960 m / 1.8 km	Used the least powder; the most widely used
Hwangja cannon	Piryeong chajungjeon, etc.	1,100 bo	about 1.32 km	The smallest cannon

The range of the Cheonja cannon is given as 1,200 bo in some sources and 1,300 bo in others. Wikipedia converts 1,300 bo to about 1.4 km, a little lower than the conversion used in this post (1 bo ≈ 1.2 m, about 1.56 km). The difference seems to come from the standards for the bo and the cheok varying slightly by period and source, and it is hard to say for certain which is correct. What is clear, as the name daejanggunjeon ("great general's arrow") suggests, is that it was the largest and longest-reaching of the Joseon cannons.

The Hyeonja cannon is said to have reached 800 bo (about 960 m) when firing a chadaejeon, and up to 1,500 bo (about 1.8 km) with the lighter chajungjeon. Because it used little powder yet was highly efficient, it was the most widely used cannon in the Joseon navy.

The Pyeonjeon: An Arrow That Flew Farther Because It Was Short

The pyeonjeon, often called the aegisal ("baby arrow"), is an arrow much shorter than an ordinary one. It was shot through a guide tube called a tonga (筒兒), and being short and light, it flew fast and penetrated deeply. Woori History Net, run by the National Institute of Korean History, records that it "flew more than 1,000 bo and struck the enemy." 1,000 bo is about 1.2 km. Joseon was extremely wary of the technique of shooting the pyeonjeon leaking out to enemy states, which also shows how powerful it was in real combat.

Admiral Yi often shot the pyeonjeon himself. The Nanjung Ilgi, his war diary, records many times when he trained by shooting iron arrows, the pyeonjeon, and the bow together.

The Bigyeokjincheonroe: Firing a Time Bomb

The bigyeokjincheonroe was a weapon made around 1591 by Yi Jang-son, a cannon maker at the Royal Armory. A round, gourd-shaped iron body was filled with gunpowder and iron fragments, and the time of the explosion was set by adjusting the length of the wound fuse. Fired from a cannon such as the daewangu mortar, it burst near the target after a delay. Its range is said to have been about 500–600 bo (about 600–720 m).

In September 1592, Bak Jin first used it in combat in the battle to retake Gyeongju Fortress, inflicting heavy losses on the Japanese. It was later used in battles such as the Siege of Jinju as well, and is counted as a weapon the Japanese came to fear considerably.

The Japanese Matchlock, and the Sekibune Had No Naval Guns

The matchlock, the main personal firearm of the Japanese army, could hit a target with accurate aim at around 50 m, as I discussed in the earlier post. Loading powder and ramming the ball was complicated, so even a skilled gunner could fire only one or two shots a minute. Within that distance, however, its penetrating power was very strong, which made it a dangerous weapon in close combat and in land battles.

But comparing only the range of the matchlock is not enough. Japanese ships hardly had naval guns that could be mounted on board the way Joseon ships did in the first place. The sekibune, the main warship of the Japanese navy, mostly could not carry cannon at all, and even the larger command-class atakebune is said to have carried only one to three guns in some cases. This was because the structure of Japanese ships, built of Japanese cedar with iron nails, could hardly withstand the recoil of cannon fire.

On top of that, the atakebune was used mainly not as a main warship but as a flagship carrying the commander. So not many atakebune actually took their place in the battle line. Ships that could carry naval guns were rare, and it was rare for even those ships to go into the thick of the fighting.

The cannon carried on the atakebune belonged to a different lineage altogether from the Joseon cannons.
Until the end of the fifteenth century, Japan had almost no large cannon technology of its own. The guns it used were most likely of the type called the bullanggi (佛狼機砲, "Frankish gun"), a small breech-loading cannon developed in Europe and brought in by Portuguese merchants through the Nanban trade. It was around 1586 that Ōtomo Sōrin, a daimyo of Kyushu, defended Usuki Castle with a breech-loader he nicknamed Kunikuzushi (国崩し, "destroyer of provinces"), which means Japan had only just begun to get its hands on such guns a few years before the Imjin War broke out. Being breech-loaders, these guns loaded quickly, but even the large ones are known to have had a range of only 500 m to 1 km, falling short of the Joseon Cheonja and Jija cannons. Joseon's cannon, systematized with its own technology for nearly 150 years since the reign of King Sejong, and Japan's cannon, only recently brought in from another country, differed from the start in the sheer amount of accumulated time behind them.

Even if the Japanese had captured Joseon's Cheonja, Jija, Hyeonja, or Hwangja cannons in battle, things would not have been much different. As we saw above, these were cannons that hurled large, heavy projectiles like the daejanggunjeon with a strong powder charge. That also means their recoil was great. Unlike the panokseon, which was joined with wooden pegs that absorbed the shock, the hull of the atakebune, rigidly fastened with iron nails, would have had trouble withstanding that recoil. Even with the cannon in hand, it would have been useless if the ship could not bear it.

The Joseon panokseon, by contrast, was sturdily built of pine and wooden pegs, and could carry several Cheonja, Jija, Hyeonja, and Hwangja cannons on its deck and fire them. Comparing the cannon alone, the gap in strength was large.

Long-Range Naval Gunnery

Joseon's cannons flew 800 bo (about 960 m) at the short end and up to 1,500 bo (about 1.8 km) at the long end, and the pyeonjeon too exceeded 1,000 bo (about 1.2 km). The matchlock, on the other hand, could hit accurately at around 50 m, and the sekibune, the main Japanese warship, did not even have naval guns. Whichever figures you take as the basis, the gap is about twenty times the range of the matchlock.

The reason Admiral Yi made long-range naval gunnery the basis of his tactics was that it was a way of making the most of the Joseon navy's strengths while exploiting the enemy's weaknesses to the full. The saying "Know the enemy and know yourself, and you will win a hundred battles out of a hundred" seems to fit it exactly.

But Admiral Yi did not always fight only with long-range gunnery.
On the day of the Battle of Myeongnyang (September 16, 1597), the Nanjung Ilgi records that the ship of An Wi, the magistrate of Geoje, was surrounded by two enemy ships and fought at close quarters.

"The enemy commander directed two of the ships under him to cling to An Wi's ship all at once, like ants, each striving to climb aboard first. An Wi and the men on his ship fought with all their might, some striking with clubs, some stabbing with long spears, some hurling chunks of water-worn stone in a wild melee, until the men on the ship were utterly exhausted, and seven or eight of An Wi's oarsmen jumped into the water and swam, and it seemed they could hardly be saved." (Nanjung Ilgi, September 16, 1597)

The principle was to overwhelm the enemy with cannon from far out at sea, but that day, when thirteen ships stood against one hundred thirty-three, things were different. Among the many naval battles Admiral Yi commanded, close-combat records remain for only two: this Battle of Myeongnyang, and the Battle of Noryang, the last battle, in which he was killed.

For a commander who held consistently to long-range naval gunnery, Myeongnyang and Noryang were that exceptional.

👉 Next post: ㉚ The Differences Between the Original Draft and the Jeonseo Edition of the Nanjung Ilgi

— Momcheolhak