Chapter 59: New Weapons (7)
"Making the Bigyeokjincheonroe in the original way is too inefficient."
The original Bigyeokjincheonroe used a sphere made from a single casting. By Hyang's 21st-century standards, this was a method with many problems. Of course, creating a hollow spherical shell was technically excellent, but in terms of production efficiency, it was not a method he would recommend.
"In terms of performance, 'shut up and mass produce' is clearly better, so I need to use numbers."
The first measure Hyang took was to split the Bigyeokjincheonroe's sphere into two halves.
Hyang changed the design to carve female threads on one hemisphere and male threads on the other. It was a method where matching and turning the threads engraved on the two hemispheres would complete a single sphere.
Hyang also applied threading to the parts where the time fuse would be inserted and the hole for loading gunpowder. He engraved threads on the lid that would cover the mounted time fuse and the cover that would seal the gunpowder hole, making them fix more securely.
Hyang took the prototypes made this way and proceeded to firepower testing.
"First, let's try without the firing process from the Wangu."
"Yes, Your Highness."
As a result of the test, the improved Bigyeokjincheonroe exploded magnificently as Hyang had expected.
"It is amazing!"
"How about sending it to the North immediately?"
Seeing the test site turned into chaos, Lee Cheon and Choi Haesan could not stop expressing their admiration. However, Hyang shook his head with a smile.
"There are still many things to test. We need to conduct firing tests first."
"Firing... I see. I forgot about 'Bigyeok' (flying strike)."
In the subsequent firing test, the Bigyeokjincheonroe was safely launched. After confirming the results, Hyang moved on to the next task.
"Now we should report to His Majesty and proceed with deployment..."
"Alright! Then shall we reduce the thickness of the shell? Let's start by reducing it by 5 ri (1.5mm) at a time."
Following Hyang's command, the craftsmen created prototypes with shell thickness reduced in 5 ri increments, starting from 5 ri down to 4 chil (4 tenths of 1 chi, approximately 1.2cm). It was literally a process of embedding knowledge through trial and error.
"Among the Wangu that fired with twice the amount of gunpowder as Your Highness commanded, the thinnest thickness that withstood from firing to impact was the one reduced by 3 chil (approximately 9mm)."
"Then shall we test it with gunpowder loaded this time?"
"Yes, Your Highness."
In the following test, the Bigyeokjincheonroe with 3 chil reduced thickness withstood the impact of firing and landing, and exploded properly. Seeing the results, Choi Haesan and Lee Cheon grew greedy again.
"The results are good, so we should report..."
"The explosion radius is too wide. There's a risk of friendly forces being damaged. Let's research ways to reduce the explosion radius while increasing lethality."
"Your Highness's command is correct. We will contemplate it."
Hearing Hyang's command, Choi Haesan, Lee Cheon, the military officers, and craftsmen began searching for various methods to find the optimal solution. However, finding a method that simultaneously satisfied the contradictory conditions of 'enhanced lethality' and 'reduced danger radius' was difficult.
Eventually, Hyang had to step forward again.
"Please bring clay, paper, and egg-sized Joran-hwan (fragmentation pellets). The Joran-hwan must be made of iron."
"...Yes, Your Highness."
When the craftsmen brought the materials, Hyang gave them orders.
"Apply clay about half a chi thick on the inside of the Bigyeokjincheonroe's shell, and densely embed the Joran-hwan. Then, when the clay dries, apply paper to firmly fix them so they don't fall out."
Hearing Hyang's command, the military officers and craftsmen immediately exclaimed in admiration.
"Ah! There is such a method!"
In the subsequent test, the modified Bigyeokjincheonroe had a reduced danger radius compared to the first one made, but its lethality was further enhanced. Hyang, examining the results, turned to look at Choi Haesan and Lee Cheon.
"Let's modify it a little more. Just a little more..."
"Yes, Your Highness."
In the ensuing second modification, Hyang and the craftsmen engraved grid-like grooves on the inside of the Bigyeokjincheonroe's shell. Then they laid another layer of Joran-hwan.
After completing the second modification and seeing the results of the following test, Hyang commanded Choi Haesan and Lee Cheon.
"This seems sufficient. If we proceed further, future generations will think of us as bloodthirsty and immoral people."
"That is correct!"
At Hyang's words, Choi Haesan and Lee Cheon nodded vigorously. The scene created by the Bigyeokjincheonroe that had undergone this modification was, in itself, a picture of utter devastation.
"Then now we should report..."
"Now let's modify the cannon that fires this explosive shell."
"Excuse me?"
At Hyang's words, Choi Haesan and Lee Cheon made bitter faces.
Hyang observed the Daewangu (large mortar) that would fire the Bigyeokjincheonroe.
"The amount of gunpowder entering the powder chamber is 35 yang (approximately 1.3 kg)... The problem is that it's not an efficient form."
What Hyang pointed out was the overall design of the Wangu.
"Let's change the structure!"
Hyang designed the cannon to fire the Bigyeokjincheonroe in a traditional linear shape. He also created a carriage similar to those mounted on 18th-19th century Western cannons.
"Is it too Western-style? That doesn't seem right."
Looking at what he had drawn, Hyang tilted his head. To be precise, the design Hyang created was closer to the infantry heavy cannons that Joseon made during the Daewongun era.
Hanging up the drawing of the cannon and carriage he had conceived, Hyang exchanged opinions with Choi Haesan, Lee Cheon, and the craftsmen.
"We mount it on a cart with large wheels. Mobility will improve."
"In dealing with the Jurchens in the North, if the cannon's mobility improves, wouldn't it become much easier?"
At Hyang's words, Choi Haesan and Lee Cheon nodded. Thanks to being men with ample real combat experience in both the south and north, the two could immediately understand the advantages Hyang spoke of.
Lee Cheon, looking at the drawing, concluded.
"We make a cart to mount the cannon, and a cart to carry the explosive shells and gunpowder... If even just two Bigyeokjincheonroe can accompany us, the Jurchens won't dare to attempt any reckless actions."
With Choi Haesan and Lee Cheon, who could be called Joseon's foremost experts on artillery, agreeing, the development of the cannon and carriage proceeded rapidly.
The difference between the newly developed cannon and existing cannons was that not only the exterior of the cannon but also the rear part of the internal powder chamber was rounded.
"General Choi, do you remember when we first tested the explosive shell?"
"Yes."
"At that time, if you look at the soot formed on the copper plate, it extended radially. I think this means that the energy from the gunpowder explosion extends in that manner."
Thinking deeply about Hyang's words, Choi Haesan nodded.
"That seems to be the case."
"Then, if we carve the rear part of the powder chamber round like this, wouldn't the cannon become much stronger? It would have the same thickness from any angle."
Examining the blueprint carefully, Choi Haesan nodded.
"It seems worth trying."
Afterward, when the first cannon was completed, Hyang and Choi Haesan immediately proceeded to testing.
They put twice the standard amount of gunpowder in the powder chambers of the existing Daewangu and the new cannon, firmly sealed them with wooden plugs, and loaded heavy stones.
In four consecutive firings, the new cannon had no problems, but the Daewangu developed cracks at the lower corner of its powder chamber.
Confirming the results, Choi Haesan opened his writing board and wrote.
"The test results confirmed that making the rear of the cannon and powder chamber curved strengthens its internal structure. It would be appropriate to modify other cannons or design new cannons of similar form."
* * *
"...and so, this Bigyeokjincheonroe, from the explosive shell to the cannon design, everything passed through Crown Prince Hyang's hands."
At Choi Haesan's explanation, Sejong and the ministers looked at Hyang once again.
"You fellow... now you make even saying I'm surprised tiresome."
At Sejong's words, all the ministers nodded. Seeing the continuous stream of amazing devices, the ministers were in a state of exhaustion. No, the Chief State Councilors and the Minister of Taxation were calculating in advance the budget that would go into mass-producing these, and their vision was darkening.
"I would like to see this newly made cannon."
"I obey your command."
After a while, two carriages entered the demonstration grounds. The carriages were each pulled by two horses.
"The first cart pulls the carriage with the cannon mounted, and the second cart carries the Bigyeokjincheonroe and gunpowder to be used with the cannon."
"Hmm..."
Listening to Choi Haesan's explanation, Sejong examined the carts. On the cart connected to the carriage, two wooden boxes were loaded.
"Those boxes contain the explosive shells and gunpowder to be used immediately after positioning the cannon."
The soldiers opened the lids of the boxes on the cart. Looking into the boxes, Sejong's eyes caught small pouches.
"What are these pouches?"
At Sejong's question, Choi Haesan opened a pouch and took out its contents.
"This is the fuse to set the time until explosion, the wooden fuse holder to wrap the fuse, 1 yang of Gap-sik gunpowder to ignite the Eul-sik gunpowder, and the paper tube to contain all of this and insert into the Bigyeokjincheonroe."
At Choi Haesan's explanation, Sejong nodded.
"I see. Eul-sik gunpowder doesn't ignite from a fuse, so you use Gap-sik gunpowder to light it. But a paper tube?"
"At first we used bamboo, but there were problems with uniformity, so we made tubes from paper."
"I see. That is a good idea."
"It was Crown Prince Hyang's insight."
When Choi Haesan credited Hyang, Sejong turned to look at him.
"Your effort is visible."
"It is the achievement of General Choi, General Lee, the military officers, and the craftsmen."
Hyang was giving credit to the soldiers and craftsmen.
Sejong's eyes, while examining the cannon, stopped at its rear. What caught Sejong's interest was the part connected to the cannon's base. There stood a pillar with threads engraved, and next to the various connected gears was a handle similar to a reel. And beside it was a semicircular disk with the Chinese characters 'Won (Far), Geun (Near), Chogeun (Very Near)' written on it.
"Crown Prince, what is this used for?"
"Yes, that is for adjusting the cannon's angle to control the range."
"Control the range?"
"Yes. You do it like this."
As Hyang turned the reel-like handle round and round, the cannon muzzle moved up and down. Watching this, Sejong turned his head.
"You adjust the angle of the muzzle like this to control the distance?"
At Sejong's question, Choi Haesan standing beside him answered immediately.
"That is correct, Your Majesty."
"How?"
"It is the same principle as shooting an arrow. When hitting a distant target with a bow, don't you raise the bow and shoot in an arc?"
"Ah!"
At Choi Haesan's explanation, Sejong nodded and exclaimed in admiration. Choi Haesan explained while pointing to the semicircular range gauge.
"By adjusting the muzzle angle according to these markings, you can control the distance from 300 to 500 paces."
At Choi Haesan's explanation, Sejong, examining the markings carefully, turned to look at Choi Haesan and Lee Cheon.
"You must have put much effort into determining these markings."
"That is correct."
At Sejong's words, Choi Haesan and Lee Cheon nodded.
To accurately quantify a fact discovered by chance—though it was chance mixed with Hyang's intention—Choi Haesan, Lee Cheon, and the craftsmen fired hundreds of Bigyeokjincheonroe.
To reduce unnecessary gunpowder consumption, Bigyeokjincheonroe filled with dirt and gravel flew through the air ceaselessly, and in the end, nearly a hundred Bigyeokjincheonroe that couldn't withstand metal fatigue and broke had to be newly made. That wasn't all.
A significant number of cattle raised by farms near Area 51 died from stress caused by the explosive sounds, and a considerable amount of wealth had to be paid as compensation. And the meat from those dead cattle was served on the tables of craftsmen and soldiers.
"If we can adjust the range like this, it will show better effects in battle. Can this be applied to other cannons as well?"
At Sejong's question, Hyang answered.
"The research institute's officials are currently researching it."
"However?"
Hearing the answer, Sejong looked for Jeong Cho among his subjects.
"Vice Director Jeong, I trust you."
At Sejong's words, Jeong Cho lowered his head and answered.
"I obey your royal command."
Jeong Cho's voice was filled with moisture as he answered.
'I still can't go home even now...'
Thanks to Hyang having already given the same command, the research institute's officials were clutching books recording the artillery results and fighting a 'war with numbers.'
Hyang's command was to investigate the changing distances in all sorts of diverse and bizarre situations, create tables, formulate equations, and create range adjustment devices for each type of cannon.
Thanks to this, the research institute's officials could only go home on designated rest days—9 days of work, 1 day off. That was only because Hyang kept this rule strictly.
However, there were also periods when officials voluntarily worked overtime. That period was when 'meju' (soybean blocks) were being fermented.
* * *
Joseon consumed enough soybean paste and soy sauce to be called 'the land of jang.' As consumption was high, every household was full of jang jars, and the residential areas of Hanseong were filled with the smell of jang. As such, the smell of jang was familiar to Joseon people. However, even for such Joseon people, the smell that came from fermenting meju was agony.
In particular, households with many family members had to ferment large quantities of meju, so the houses of high-ranking officials who kept many slaves and guests had even more severe meju smells.
The palace also fermented large quantities of meju, but since the palace had absolutely vast space, the smell of meju was not that severe. For this reason, whenever the meju fermentation season came, officials would delay leaving work as much as possible.
* * *
Anyway, thanks to the commands of Sejong and Hyang, Joseon became the first country in the world to create and apply firing tables for cannons.
Having examined everything from the cannon firing the Bigyeokjincheonroe to its ancillary equipment, Sejong straightened his posture.
"Hmm, I think I've seen everything I need to see, but before checking the ledgers, there's one last thing to confirm. The armor worn by the military officers and soldiers here is different from what I've seen before, so explain this."
"We have prepared. I will guide you."