Mortars and Musinpo
Weapons being his field of expertise, Hwiyeom went so far as to draw up the cannon blueprints himself and hand them over to the Innovation Hall.
Thanks to his interference, the order of development had been turned completely upside down—but this was the same Innovation Hall that had already produced matchlocks, flintlock muskets, and even a Gatling gun. One might well ask why they were still tearing their hair out over something as simple as a cannon. Yet they had no shortage of problems to wrestle with.
What Hwiyeom demanded of them was a muzzle-loading smoothbore cannon.
A breech-loading rifled piece would have required several technologies just to keep the breech from failing under the pressure and gas of the explosion—and for a workshop only just beginning to make artillery, that was far too much to ask. Having a design in one's head and actually building the thing were two entirely different matters.
Rifling the barrel to extend range was likewise out of the question for the moment. Unlike modern machining, which cuts rifling with precision and seats a shell that fits without a hair of play, early rifled guns in the original history had required the round to be hammered into the grooves just tight enough that the propellant gas wouldn't simply blow past. Only then did the rifling do its work—much the way a flintlock musket's ramrod still had to be driven hard to seat a ball against the rifling.
And Hwiyeom intended to fire munitions filled with poison gas—mass-killing shells fitted with impact fuzes (a porcelain vial of nitric acid solution nested among black powder) so that they would burst on contact and scatter their contents far and wide. Trying to ram a shell like that into a rifled barrel was an invitation for everyone present to die together.
So he ordered them to produce a muzzle-loading smoothbore of the type known in Joseon as a wan-gu, a bowl-mouthed piece. Even that was no easy task.
How large should the bore be? How long the barrel? How many catties of powder made for a good charge, and what was the greatest charge the tube could survive at maximum range? How many rounds could it fire at that extreme before it failed? How did one improve accuracy and lengthen the gun's service life? The questions Hwiyeom could not answer for them piled up like a mountain.
In the end they had no choice but to burn through vast quantities of steel and powder, blowing things up, and learning by trial and error.
Which is to say: Dang Unhwa was in paradise.
"Oh—ohhhh! The poetic inspiration is pouring forth!"
Inspiration and engineering shared nothing but a first letter, yet Unhwa trembled like a master of letters seized by a rapture of verse, pouring out new drawings and calculated figures without pause. Most of those designs were idle fantasies—but a few of them looked familiar to Hwiyeom's eye.
"Look at this—a fougasse married to a Flying Thunder Cannon? And this—this is a portable mortar."
In its original form a fougasse had been a primitive claymore of sorts, used before true artillery existed: dig a pit, pack it with powder, heap gravel on top, and detonate it to fling a broad swath of damage into the enemy. A cannon, in a sense, was simply that same idea given a cylindrical barrel so the force of the blast could hurl a projectile instead. One might almost call the fougasse the ancestor of the gun.
Of course Unhwa had arrived at the idea by pure contrarian genius. Faced with the difficulty of calculating how much powder a barrel could withstand, he had simply asked, "Then why have a barrel at all?"
And his fougasse was no mere hole in the ground. He proposed casting a pot-shaped mold of concrete, packing powder into it, laying a wooden board over the charge, heaping stones or scrap iron on the board, sealing the whole thing with another board, and half-burying the assembly before setting it off.
The concrete-pot method bore a striking resemblance to the feileipao—the Flying Thunder Cannons of China's civil war, which had recycled oil drums as mortar tubes. Of course, unlike those pieces, this version was strictly single-use; concrete could never survive the shock of the blast more than once. Even so, it offered far better directionality than a simple earthen pit, channeling the blast forward with excellent effect.
A broad-front killing weapon fired by a long fuse—closer to a claymore than to a true cannon. Build them in the rear, ship them forward, and they could be used anywhere: buried in the ground, propped against a wall in a hurry, or even lit and dropped from a battlement.
Years ago we built a prototype claymore with Explosive Poison and never got a proper chance to use it.
Unhwa's design was christened the Musinpo—the Bodiless Cannon, a gun without a barrel.
After a moment's thought, Hwiyeom added a few notes to the drawing. Since the weapon was being built with the Chagatai horse-armies in mind, he ordered the interior packed not with scrap iron or stones but with caltrops. Scattered like shot, the caltrops would be vicious enough in flight; once strewn across the ground they would become a nightmare for any infantry or cavalry trying to storm a wall.
As for the mortar, they seemed to have skipped the cannon entirely and gone straight to making shells. The design was primitive: an oaken projectile with a propelling charge of fulminate of mercury and black powder fitted into its base—much like the paper cartridge cases stored in the secret laboratories beneath the Poison Hall—and an explosive warhead in the nose. Dropped into a slanted tube, the shell slid down until its primer struck an internal spike, the propellant fired, and the whole thing was blasted skyward on the resulting pressure.
Clever idea, but I'm shelving it. If we start flinging shells that fly without a lit fuse, the existence of mercury fulminate will be impossible to hide—you maniac.
They had already sweated blood to conceal the fulminate after the naval mines used against the Yangtze River Pirates (the authorities had spotted the clockwork and assumed the mines used a delayed fuse of smoldering cord sealed inside a waterproof casing—never guessing the springwork was a detonator). Bomb-obsessed Unhwa, eyes glazed with rapture, had clearly not considered any of that.
Hwiyeom swallowed a sigh, stamped the report Classified—proceed in secret, and sent it back.
Despite such detours, Unhwa eventually produced the framework of the muzzle-loading smoothbore Hwiyeom had wanted. Through his admirable unity of passion and profession—and a great many experiments—data accumulated on the optimal powder charge for smoothbore fire, effective range, and how many rounds a tube could endure. And once the preparations were complete? Mass production waited.
For those actually doing the work, of course, that was when the real labor began.
The Innovation Hall and the Forge Department worked through the night, night after night, to produce every piece of artillery needed for Yunnan and Sichuan. Even with molds casting the guns like stamped goods, it was a brutal forced march.
As always, the Innovation Hall and the forges came whining to Hwiyeom for relief. As always, he was unmoved.
"Want to try that speech in front of the Chagatai cavalry? Ask them to invade a little later so we don't have to work overtime?"
No one knew when the enemy would come, and without at least some training with the finished guns there would be no point fielding them at all. Unable to curse Hwiyeom to his face, the craftsmen instead heaped colorful abuse on the faceless horsemen they had never met—and swung their hammers through the night.
The peculiar thing was that the Construction Department, which usually watched these scenes with a shrug and a muttered "better them than us," joined the ordeal this time. Gwak Do, head of Construction, stormed in to Hwiyeom in a towering rage.
"What is this? Why are you putting my people on weapons work? We've got our own construction schedules—who am I supposed to finish anything with if you keep doing this?"
Hwiyeom was unrepentant. He met Gwak Do's glare with transparent, untroubled eyes.
"Is there anyone in the Central Plains who mixes concrete better than the Construction Department?"
"…"
It was all because of Unhwa's Musinpo. The concrete molds meant there was no more efficient way to produce them than to put Construction's people on the job. In the end Gwak Do could only groan and retreat.
Hwiyeom even improved Unhwa's design and handed them a new assignment.
"If you want to project both the blast and the backblast as far forward as possible, a round barrel is still the right shape. But since these are single-use pieces, and even a shallow wound can put a man out of the fight—what about something like this?"
What he sketched was a ladder-shaped concrete frame cast in wooden molds: a row of square cells joined edge to edge, rather like a pill organizer. The design was far easier to mass-produce, and the rectangular blocks stacked and shipped cleanly, then fixed in place for firing without fuss.
If we load the powder in advance, the black powder will pick up moisture, and the iron weight will make the whole thing a pain to handle… so we separate the charges.
He divided the munition accordingly. Into a canvas satchel the size of a schoolbag went a wax-sealed charge of powder, then a full measure of caltrops, the mouth closed. Slot the bomb-bag into an empty cell of the concrete block, open the bag, and a coiled fuse unspooled from within. Draw it out as far as it would go, light it, and fall back—the flame would race down the cord, kiss the powder, and detonate with a boom.
Hwiyeom named it the Ladder Musinpo.
It was built for mass production, but it was no joke as a killer. The provincial military commander of Yunnan had come to the demonstration with his arms crossed and a skeptical sneer, ready to see how impressive this wonder really was. When the lit fuse burned for what seemed an age without result, he laughed and muttered about a dud—then nearly jumped out of his skin when the Musinpo finally roared.
Five blocks detonated at once. The forward blast shredded every straw dummy within thirty paces into flying tatters, and the caltrops sailed nearly a hundred paces. Considering that a modern claymore's effective kill radius is about fifty meters and its maximum range two to three hundred, the performance was excellent.
Hwiyeom felt a complicated pang—he had set out to build a cannon for poison gas and somehow invented a more versatile, easier mass-killing weapon instead—but there was no helping it. Only a few months remained before the enemy arrived. However devastating poison gas might be, too few cannons would leave them dangerously thin. The concrete claymores—the Ladder Musinpo—used no iron in the barrel, could be produced on an entirely separate line (rumor had it Gwak Do was beginning to contemplate murdering Dang Unhwa), and outstripped anything else in sheer volume of output.
And that was the foundation—and the confidence—behind Hwiyeom's words to Yunnan's military commander: "Let's start with three thousand gates."
By contrast, the test firing of the poison-gas artillery was a quieter affair. At the signal a thunderous report sent a heavy bolt soaring an impressive distance; it struck the earth, and with a modest crack a pale yellow-green cloud billowed up. Knowing nothing of the gas's true menace, the provincial commander was unimpressed.
To change his mind, Hwiyeom had a flock of sheep penned and lofted a chlorine shell into their midst. When the cloud cleared and the commander walked the ground, he stared open-mouthed at the sheep that had died in heaps, blood frothing from their mouths.
"I've heard the Dang Family was famous for its poisons, but…"
"You'll be buying, then?"
The commander nodded.
"As many as we can get."
The bill would go to the Emperor in any case. When he signed the purchase order, his hand no longer hesitated.
And so, after all the twists and turns, the new weapons began to move out across Yunnan and Sichuan—while summer drew toward its end.
In Yunnan and Sichuan the preparations to stop Chagatai were proceeding steadily. The problem was Qinghai Province.