The Torpedo Was the Problem, Not the Water
“What kind of lunatic barges into someone else’s celebration and starts wrecking the mood like this? Handing over the supercavitating torpedo project wholesale? You’re planning to swallow a national project we’ve spent three full years on?”
Chairman Song Tae-hwan’s roar tore through the night air over Geoje Island.
The open lot, which had moments ago been thick with the smell of steak and laughter, turned to ice in an instant.
Chairman Cho merely looked at the enraged man huffing like a cornered beast and laughed with easy amusement.
“Swallow it? The Chief of Naval Operations came asking for help. I’m just lending out one of my valuable people. You said yourselves that after pouring in hundreds of billions, you still couldn’t even control the vibration and were about to sink the whole project, didn’t you?”
“You…!”
Thick veins stood out on Chairman Song’s forehead.
His gaze shifted to me, standing calmly beside Chairman Cho.
It was a fierce, cutting look.
“You’re Executive Director Baek, then? You fixed a little submarine piping vibration and now you think you’re something special? This is a torpedo that tears through water at 300 kilometers per hour. You’re not some fool who’s been carving tank armor for life; this isn’t something you get to touch lightly!”
At Chairman Song’s harsh bark, the Solaris employees nearby held their breath.
Plant Director Go Kwangsoo, too, did not meet my eyes.
He had been all smiles aboard the submarine, praising me to the skies without end, but when it came to a matter of corporate pride between companies, it seemed he couldn’t help himself.
Still, I did not back away from Chairman Song’s pressure.
“Chairman.”
“What.”
“Speaking as the kind of man who used to carve tank armor, a torpedo is, in the end, just a tube that cuts through fluid resistance, and a machine whose vibration has to be controlled.”
At my calm reply, Chairman Song’s eyebrows twitched.
“Were you so focused on speed that you missed the gas-injection balance of the front-end cavitator? The thickness of the bubble envelope around the hull became asymmetrical, so the stern started rubbing against the water, creating eccentricity. In the end, it probably destroyed itself through severe vibration.”
For a moment, Plant Director Go’s shoulders jerked.
I went on, piecing together the fragments of the footage the naval chief had shown me in my head.
“It’s fundamentally the same as an active suspension system in a tank controlling irregular road shock, or submarine piping canceling fluid pulsation. If you can’t actively control the trajectory drift that occurs at the interface between water and gas, then failure is the natural result.”
“You’re just all talk, and you sure love hearing yourself speak!” Chairman Song shouted.
“You’ve never seen a single piece of data or laid eyes on the actual hardware, and yet here you are spouting textbook nonsense! Do you think the field is some kind of joke?”
Then, at last, Chairman Cho, who had been standing with his arms folded and watching silently all this time, let out a dry laugh as if the whole thing were absurd and stepped forward.
“Listen here, Chairman Song.”
“Don’t meddle.”
“He’s my employee, and this is our company’s matter. Of course I should meddle. If I don’t, who will?”
Chairman Song’s face twisted.
But Chairman Cho only kept talking.
“The employee you’re calling a textbook-spouting windbag is the one who kept your 4,000-ton submarine alive. You’re on the verge of being abandoned by the Navy because you couldn’t even control a single torpedo, and this is the time to be nursing your thin little pride?”
Chairman Song ground his teeth and glared at him.
That was when the suffocating silence between the two titans of industry was finally broken.
“Chairman….”
From the corner, quietly standing apart until now, Senior Researcher Seo stepped forward.
As an ADD man, he had no reason to worry about the chairmen’s temper.
“What Executive Director Baek just pointed out, the eccentricity caused by asymmetrical bubbles and the lack of a control logic for it... matches exactly the failure-prediction simulation results we ran on our ADD supercomputer for the past two months.”
Seo’s one decisive line landed like a nail driven into the board.
Chairman Song’s face twisted hard.
“The situation may change later, but at this point, I think it would be wise to at least let Executive Director Baek take a look at the problem. Developing the supercavitating torpedo is important not only for Solaris, but for the Republic of Korea as well.”
“...We can do it ourselves.”
As though he could not bear to hurl insults at Seo, too, Chairman Song forced the words out through a face taut with swallowed fury.
Seo glanced at me briefly before continuing.
“Of course. I’m confident of that as well. But as you know, the international situation is moving fast. At a time like this, what matters is completing it as quickly as possible.”
“……”
The corners of Chairman Song’s mouth trembled.
His expression, which had looked as if he was about to grab someone by the collar, was now crumpled in disgust as though he had bitten into something rotten.
The Navy’s pressure. ADD’s technical agreement.
And on top of that, my own insight, which seemed to have pierced straight through the problem without even seeing the hardware once.
For Chairman Song, every escape route had been sealed shut.
He drew in a deep breath, then irritably yanked at his tie.
“...Fine. Go on, then.”
He growled at me.
“I’ll be watching closely to see whether you’re the real deal or just some fraud who picked up other people’s data and won’t shut up.”
He spun on his heel and barked at Plant Director Go.
“Director Go! Open the tank test facility immediately! Let’s see with our own eyes how this great Hanseo Defense executive director plans to tear apart and rebuild our torpedo!”
As I watched Chairman Song storm off into the dark, Chairman Cho patted my shoulder.
“You saw that, right? I cleared the path properly. Now it’s your turn.”
“Thank you, Chairman.”
“If you’re thankful, then succeed. Though it’s not likely, if you fail after this, I’ll be harassed by that hot-tempered old man until the day I die.”
With a chuckle, Chairman Cho walked away.
Then Cho Yerin came over to me.
“I’m rooting for you, Senior.”
“You’re heading back?”
“Mm-hm. Since Dad’s here, I should go with him. What kind of rumors do you think I’d get if I stayed?”
A grown woman hanging around a strange man, and not just any man, but a divorced one staying alone at a lodging in the provinces. What sort of disgraceful time was she spending there?
Probably something like that.
I nodded.
“Thanks for the sushi. I’ll enjoy it.”
“Mm. See you after you’re done.”
“Yeah.”
Cho Yerin headed toward the helicopter with Chairman Cho.
I watched the helicopter carrying the two of them fly north toward Pangyo for a while.
“Shall we go?”
Plant Director Go approached me and said.
“Yes, let’s.”
* * *
After following Plant Director Go Kwangsoo for a while, the elevator we were in descended toward the basement with a rough mechanical groan.
Where we were headed was 40 meters underground, the highest-security zone at Solaris Marine, carved into a thick layer of bedrock.
The elevator arrived there, and the moment the doors opened, a strange air, cool yet tinged with machine heat, brushed my cheek.
“This way, Executive Director.”
Following Plant Director Go’s guidance, I passed through a thick blastproof door.
The first thing that came into view was a gigantic sealed tank stretching hundreds of meters.
And surrounding it, filling the walls, were supercomputer servers and measurement instruments.
It was the kind of scale that practically reeked of money.
It certainly looked like the site of a national project that had burned through hundreds of billions.
But what caught my attention wasn’t the flashy equipment.
It was the man standing in the middle of the tank control room, staring daggers at me through sharp silver-rimmed glasses.
Senior Researcher Yoon Jin-ho, the fluid dynamics PhD in charge of the supercavitating torpedo project.
Even after our eyes met, he offered no greeting.
His sharp gaze ran me up and down.
It was a naked show of displeasure at an unwelcome intruder, especially one ground-down field engineer from the land systems side daring to set foot in their territory.
“Executive Director Baek Gunwoo, I’ve heard your name. I know the field has to obey when orders come down from above, but to be honest, this is disappointing.”
“...Disappointing?”
“Yes. This place is on a completely different level from land equipment that just rolls around on tracks. Supercavitation is the extreme, the pinnacle of fluid dynamics. It’s not an area where an outsider can come in and start offering advice.”
At the thorny provocation, I gave a bitter smile.
After more than a decade of cutting steel and wiping down grease, I had learned one thing.
In front of a machine, pride spoken with the mouth was useless.
“Well, I can understand why that would bruise the pride of a bunch of PhDs.”
I strode past Senior Researcher Yoon toward the main monitor in the control room.
“Let’s take a look at why that glorious pinnacle of fluid dynamics keeps smashing into the tank wall. Pull up the latest failure data and the high-speed camera footage.”
“……”
At my shameless request, Yoon’s brow tightened, but he gritted his teeth and tapped away at the keyboard.
“Have a look. And if you can tell us what’s wrong after that, I’ll be sincerely grateful.”
Moments later, footage began playing on the large screen.
Shooooom—!
The torpedo burst from the launch tube and shot straight through the tank at terrifying speed, slicing through the water.
Gas jetted from the front end, enveloping the hull in a bubble layer that erased drag from the water.
The speed was astonishing.
But then.
The moment it tried to adjust course toward the target, the bubble layer wrapped around the stern suddenly collapsed.
As soon as the exposed tail fins touched the water wall, the entire torpedo shattered apart.
“Our control algorithm is perfect.”
Senior Researcher Yoon protested in a voice thick with bitterness.
“We solved tens of thousands of equations, and the hardware error rate is zero. Look at the sensor logs. There was no pressure drop and no motor-control error.”
“Really?”
“Yes. And yet once it passed 300 kilometers per hour, the interface between the bubble and the water collapsed at random. This is an irregular turbulence phenomenon from outside fluid flow, a chaotic zone even a supercomputer can’t predict. How are we supposed to control that?”
Chaos. Random turbulence and collapse.
It meant utterly uncontrollable motion, where countless variables tangled together until no mathematical trend could be found.
Instead of answering, I leaned closer to the screen.
Nothing in this world happened without a cause.
There had to be a reason this was happening.
Thinking that, I narrowed my eyes and focused on the frame in which the torpedo exploded.
And what I saw was not what Yoon had described as random turbulence from outside.
The smooth blue bubble layer covering the torpedo’s stern.
That part was perfect.
The problem came after that.
The propulsion motor inside the torpedo.
From there began a glaring red high-frequency vibration, something that could only be called an acoustic wave, racing madly along the hull’s metal skeleton toward the stern.
The instant that red wave reached the tail fin.
It slammed head-on, and at a perfectly wrong rhythm, into the natural frequency of the blue bubble layer.
Crash.
Like a hammer smashing glass, the vibration generated inside was tearing the bubble layer apart from within.
I slowly let out a breath and had no choice but to straighten up.
That was the cause.
They had looked only at the energy coming in from outside and missed the vibration coursing along the frame, destroying everything from within.
Now that I knew the cause, it was time to provide the answer.
I turned to Senior Researcher Yoon and spoke.
“Remarkable.”
“What?”
“There isn’t a single error in the software or the algorithm. The mechanical error really is zero.”
At my honest acknowledgment, Yoon blinked in surprise.
“But while you were fighting the water outside, you missed the enemy inside.”
“The enemy inside?”
“The bubble layer isn’t collapsing at random. High-frequency vibration from the torpedo motor is traveling through the hull to the stern, and that vibration frequency happens to match the natural frequency of the bubble layer there, so it’s breaking the bubbles apart on its own.”
I tapped the monitor with my finger and pinned the fact in place.
“This isn’t a flow problem. It’s an acoustic resonance problem.”
At that instant, Yoon’s expression stiffened.
He let out an incredulous laugh.
“Ha! The motor’s vibration is breaking the bubbles? Executive Director Baek, the bubble layer around the torpedo is filled with high-pressure gas. Gas transmits vibration far less efficiently than liquid or solid!”
A sharp rebuttal from a real expert.
He wasn’t wrong, exactly.
As I nodded, Yoon continued.
“Besides, the motor mount was already designed with isolation to suppress mechanical vibration. Saying some tiny residual motor vibration is punching through the gas layer and destroying a bubble envelope that can withstand deep-sea pressure is just nonsense from a fluid dynamics standpoint!”
“That would be true if it were calm, still gas.”
I met his eyes squarely and pushed back.
“But this thing is slamming through deep-sea pressure at 300 kilometers per hour. Do you really think that boundary layer is intact gas? It’s basically a mud pit, with water and bubbles tearing each other apart and mixing together like mad. And motor vibration isn’t some low rumble. It’s a high-frequency wave, a kind of shivering current running through the hull.”
I pointed toward the stern fins on the monitor.
“The entire outer hull has become a giant ultrasonic cleaning plate. That ultrasonic vibration is hammering the muddy mix of water and gas, and inside it the bubbles are bursting on their own, ripping the whole membrane apart.”
“……”
The instant my words fell.
Yoon froze in place as if he’d been struck hard on the back of the head with a sledgehammer.
“The hull became an ultrasonic plate and struck the multiphase fluid interface... My God, then this was a chain explosion caused by acoustic cavitation?”
His lips trembled.
In his mind, the hypothesis I’d just thrown down and the unexplained failure data they’d accumulated over all this time were probably slamming into place at a frantic pace.
As if possessed, Yoon reached for the keyboard.
With a rapid staccato of keys, the simulation parameter window sprang onto the giant screen.
He pointed at it with shaking fingers.
“Pressure, flow rate, turbulence modeling... We put in everything related to water.”
His voice cracked horribly.
“Hull natural frequency and wave interference... We overlooked something this basic...”
They had been crunching numbers on a supercomputer and missed the field engineer’s blind spot: the acoustic waves traveling through metal.
The control room fell silent as a tomb.
The looks on the faces of the PhDs who had treated me as an unwelcome outsider only moments before were shifting into shock and awe.
The atmosphere had completely tipped in my favor.
I loosened my tie slightly and turned back to the plant director standing behind me.
Plant Director Go looked even more stunned than he had when I’d solved all sorts of problems aboard the submarine, staring at me as if I were some kind of monster.
“Director, I think we can wrap this up pretty quickly.”
“...You’re saying this can be wrapped up quickly?”
“Now that we’ve identified the problem, the rest is easy. No need to tear up the control logic.”
“Then what do we need to do?”
Plant Director Go asked cautiously.
“Just install an acoustic metamaterial pad that eats high frequency vibration at the motor mount and the stern-fin joint. A special sound-absorbing material. If you shift the wave frequency, the bubbles won’t break.”
The moment I delivered that crisp prescription, Plant Director Go, who had been numb with disbelief, trembled with excitement and shouted.
“You all heard that? Strip the damping pads from the material warehouse immediately! Let’s rebuild the mount overnight and fire it again tomorrow morning!”
“Yes, sir! Understood!”
The researchers sprang into action in perfect order.
Senior Researcher Yoon was still staring blankly at the monitor, turning over the words I had left behind.
On his rigid face, instead of defeat, there was now the pure joy unique to an engineer whose years-long blockage has finally cleared.
I smiled and dragged out a chair from in front of the main console, then sat down heavily.
Oddly enough, even though this was a completely different branch of technology from what I had done up to now, it wasn’t difficult at all.
This... might end faster than I thought.
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