The Enemy Is at 13.7 Kilometers
Wooong—
Only the low hum of the air-conditioning drifted in my ears.
A narrow metal box with no windows.
Trapped inside it, I felt as though even my sense of time had gone fuzzy.
So this was life aboard a submarine?
In movies and dramas, they only ever showed you a few carefully selected scenes, but right now I was spending my time aboard this submarine named Kim Gu.
It had already been two days since we set out.
We had left the Geoje Shipyard and were now heading into the East Sea.
Of course, even then, nothing particularly special was happening.
It felt like quietly passing the time inside a building, more than anything else.
“Hmm... calmer than I expected.”
I muttered to myself, swallowing a small yawn.
But the atmosphere around me was very different.
The person who caught my eye most was the sonarman seated in the CIC, the Combat Information Center.
He was using the sonar, an acoustic device, to listen to the sounds made in the submarine’s surrounding waters and keep watch.
And he looked as if he’d fallen into bliss, like a researcher who had finally been handed the state-of-the-art analysis equipment he’d dreamed about for years.
“Captain. This is unbelievable. I never imagined I’d actually hear sounds like this in real operations!”
At the sonarman’s words, Colonel Choi Jongil let out a dry chuckle.
It was something I’d already heard more than five times from yesterday to today.
Still, Colonel Choi seemed just as pleased, and with a satisfied smile at the corners of his mouth, he said to the sonarman, “Sonarman. Report accurately. What exactly is so good about it?”
“The masking effect caused by self-noise is practically zero. Even with the hydrophones turned all the way up, there’s no noise contamination. Right now, I could probably count how many turns an merchant ship’s propeller is making from fifty kilometers away!”
Colonel Choi burst out laughing.
“So it’s not just that your ears got sharper—you’ve become Sommers, then. At this rate, we’ll be able to pick out Chinese and Japanese submarines cruising around without any trouble, huh?”
“Haha. Of course, Captain. Leave it to us!”
Still smiling, Colonel Choi nodded and casually shifted his gaze.
At the end of that line of sight was me.
Not just Colonel Choi.
The operations officer, the sonar chief, the communications officer... every crewman in the CIC was looking at me.
Honestly... it was a little overwhelming.
It was a different feeling from the way office workers or people in our industry had looked at me in admiration and praise.
This was more like absolute trust from soldiers on the scene, where life and death hung in the balance.
An oddly warm, prickling gaze down my spine.
To hide my embarrassment, I cleared my throat and stood up.
“Ahem. I’m going to grab a meal.”
*
After a light meal in the officers’ mess, I walked through the submarine with Plant Director Go Kwangsoo.
The excuse was a patrol, but in truth I wanted to walk a little, help my food settle, and look around the interior properly.
As we passed through the narrow corridors, tangled bundles of piping and cables swept past overhead.
And there was something deeply satisfying in them.
Blue energy flowed through every one of those pipes and cables.
Nothing was clogged, nothing overloaded; everything was in perfect balance.
At this point, it looked like I had really done my job properly.
Of course, I hadn’t been involved in every part of building the submarine, but I had at least handled inspection to make sure problems wouldn’t arise.
Wasn’t that enough to say I’d done my share?
Even to myself, it felt like a gratifying result.
Beside me, Go Kwangsoo laid a hand on the wall and then on the piping, feeling the vibrations as he said, “Thanks to you, sir, this ship’s turned into a fine piece of work.”
“Me? Come on, how could it be because of me? It’s all thanks to everyone making it well.”
“Haha. I appreciate you saying that.”
Go Kwangsoo continued in a light tone.
“Still, you had a big hand in it, sir. Honestly, I’ve built ships for decades, but this is the first time I’ve ever seen one this quiet and vibration-free. Hell, I can’t even tell whether the engine’s running or not.”
“That’s because the base design was good. I just added a spoonful on top.”
When I answered modestly on purpose, Go Kwangsoo waved a hand.
We were in the middle of that warm conversation when—
Wiiii—wiiii—wiiii!
A short warning tone rang through the ship’s speakers.
From this moment on, maximum-speed maneuvering test will commence. All hands, brace for impact.
It was Colonel Choi’s voice.
The high-speed maneuvering test was a mandatory part of sea trials.
From yesterday through this morning, we had moved slowly, at a speed gentle enough not to burden the hull.
Apparently, he was now confident we could push it a little.
“Oh, looks like we’re going to run her a bit.”
“Seems that way. Hold on. We might shake a little.”
I grabbed the handhold beside Go Kwangsoo and braced myself.
Through the soles of my feet, I could feel the motor output rising.
For a moment, I even had the illusion that the massive submarine was slicing through the water and charging ahead.
Then—
KA-AAAAANG—!
KREEEEEEEEEEE—!!!
“......?!”
A horrifying roar tore out from the stern.
It was a sound I had never heard in my life, eerie enough to be truly terrifying.
Along with a piercing metallic shriek, as if some gigantic steel pillar were being forcibly twisted until it snapped, a vibration strong enough to jolt the hull shuddered through the floor.
Engine stop! Emergency stop! What was that sound just now?!
Through the speaker, the captain’s frantic shout rang out, and before long the inertia of slowing down washed over us, the noise vanishing as if it had never existed.
But in the narrow corridor where we stood, only heavy silence remained.
In the midst of it, Go Kwangsoo said in a low voice, “...Wasn’t that the sound of a shaft breaking?”
His face had gone white as paper.
*
In front of the stern engine room.
The faces of the experts hastily assembled there were the picture of despair.
“Judging by the sound pattern, I think the thrust bearing has gone.”
The chief engineer, a navy major, reported with a face drained of color.
“It couldn’t withstand the high-speed rotational load, the metal overheated and started grinding the shaft. Unless it was something else...”
“...then the reduction gears have all shattered.”
Seo, the senior engineer, bit his lip and added.
Either way, it was a fatal blow.
Colonel Choi asked in a trembling voice, “Repairs? Can we repair it here?”
“If what we’re talking about is the cause, then no. Not with local maintenance.”
Go Kwangsoo shook his head and delivered the death sentence.
“To open up the bearing or gearbox, we’d need special equipment. We’d have to turn back, put the ship back in dock, and cut open the hull to pull the engine out.”
Turn back.
On the first day of sea trials, the engine dies during the maximum-speed test and we have to be towed home?
And then they’d have to cut open the hull just to pull the engine out?
If that happened, it would be an utterly miserable, colossal failure.
At worst, it could sink the entire project.
The captain’s face was turning ashen.
“Ha... turning back one day after departure...”
When those hopeless words were being traded back and forth, I quietly approached Kim, the assistant manager who worked under Seo.
“Assistant Manager Kim. That measuring laptop—does it have the submarine’s drawings on it?”
“Huh? Ah, yes. Yes, it does, sir.”
“Let me see it for a moment.”
I took the thick industrial laptop from Kim and brought up the submarine’s integrated piping and instrumentation diagram, the P&ID.
Thousands upon thousands of lines and symbols filled the screen.
A submarine contained three million parts.
The drawings that mapped those intricate veins numbered in the hundreds of thousands.
If you printed them on paper, they’d fill a truck and still leave room to spare—a man-made labyrinth of impossible density.
If I alone were to inspect every last drawing, it would take months.
And in practice, I hadn’t reviewed them all anyway.
But right now, the problem of where to look was clear.
Let’s see...
The thrust bearing the experts suspected.
That was blue.
It was probably spinning perfectly normally.
The reduction gears.
Those, too, were blue.
Not a single tooth would be missing.
“It’s not these... so where is the problem?”
I shifted my gaze and swept over the lower section, the maze of tangled hydraulic control lines.
And before long, I found it.
A check valve no bigger than a finger, hidden among the forest of pipes.
That little thing was screaming red at the top of its lungs.
“Hold on. I don’t think it’s the bearing.”
“What?”
The chief engineer looked at me in confusion.
“That sound was that huge and it’s not the bearing? It sounded like metal grinding apart.”
Instead of answering, I handed the industrial laptop back to Kim and said to him, “Assistant Manager Kim, can you hook the DAQ directly into the LCP right now?”
“Yes, the equipment is already set up. We just need to open the port.”
Kim pulled a thick industrial interface cable from the laptop bag slung over his shoulder.
With practiced ease, he flipped open the waterproof cover on the control panel mounted beside the hydraulic unit.
Click.
The circular connector locked into the diagnostic port with a clean metallic snap.
Immediately, a complex data stream began pouring across the screen of the industrial laptop he was holding.
“The link’s up. Logging in real time.”
“Good. Then pull up the pressure graph for the hydraulic supply line versus the propulsion motor RPM. One-tenth-second intervals.”
At my instruction, Kim worked the industrial laptop connected to the data port beside the piping.
The blunt clatter of keys echoed through the cramped engine room.
“Got it!”
I turned the monitor and showed it to them.
“Look.”
The pressure curve wasn’t smooth.
In a specific range—precisely where we crossed fifteen knots—the graph wavered ever so slightly and drew a sine wave.
“If it were a bearing grinding down, the graph would jump around irregularly because of the metal shavings. But this is too regular.”
“Uh...”
Seo pushed his glasses up and leaned toward the monitor.
“You’re right? Surge? You mean fluid pulsation?”
“Yes. At high speed, the hydraulic pressure hits a certain valve and the vortex created there matches the natural vibration frequency of the piping. It’s hydraulic resonance.”
“Ha, resonance really is the worst. So the reason it sounded like the machine was breaking was because the entire piping network was vibrating like a speaker?”
Go Kwangsoo asked in stunned disbelief.
“Exactly. The metal’s fine.”
“Then... can it be fixed? Do we need to replace the valve?”
Colonel Choi asked as though clinging to the last straw.
I snorted and shook my head.
“Nothing to fix. We just need to tune it. Resonance only needs its timing broken.”
I reached into the narrow gap between the pipes.
Then I grabbed the bypass valve mounted beside the problem check valve.
“If I open this by just fifteen degrees and let some flow through, the period of the pressure wave changes. That breaks the resonance timing.”
With a faint creak, I turned the valve slightly and then looked at Colonel Choi.
“Captain, try it again.”
*
Fifteen knots, once more.
Tense silence ruled the engine room.
Everyone held their breath and strained their ears.
Shoulders tensed, waiting for that dreadful roar to burst out again at any moment.
But—
Wooong—
There was nothing but the smooth hum of the motor.
The speedometer had already passed eighteen knots.
“Huh...”
Go Kwangsoo collapsed onto the floor as though his legs had given out beneath him.
“I thought the bearing was completely shot and nearly died of fright... and it was just one valve.”
“We couldn’t tell from the data either... just what in the world are you, Director Baek...”
Seo clicked his tongue in disbelief.
Colonel Choi seized my hand in both of his.
His palm was slick with cold sweat.
“Thank you. If it hadn’t been for you, we would’ve turned back and been humiliatingly embarrassed. Really... thank you.”
The crewmen from the engineering maintenance team were the same.
The curious, wondering look they’d had when I first boarded was gone without a trace.
Now their eyes held absolute trust.
Man, that’s oddly embarrassing in its own way.
“Glad that’s sorted out. It was nothing serious.”
I answered calmly and loosened my tie.
Anyway, the internal enemy was dealt with.
Just as I was about to finally relax, thinking my real work here was done—
Beeeep—!
The intercom in the engine room burst into a sharp ring.
Colonel Choi answered in speaker mode.
“What is it?”
Contact! Bearing 0-9-2! Propeller noise detected!
Colonel Choi’s expression hardened in an instant.
The relief from just moments ago evaporated, and the killing intent of a veteran soldier took its place.
“Identify the vessel!”
From beyond the speaker, the sonarman’s frantic voice rushed on.
[Seven blades... matching rotation speed... this is... a Chinese Yuan-class (Type 039A)! Distance 13.7 kilometers, heading straight toward us! It looks like it heard the noise just now!]
China.
At that word, the air around us froze.
Then Colonel Choi looked at me and said, “Director Baek. That problem from earlier—it's completely resolved, right?”
“Of course. That sound won’t happen again. I can’t say whether there are any other problems we haven’t found yet, though.”
“I see. That’s enough.”
Colonel Choi grinned, looked at me, then at the crew around us, and said, “Let’s go to the CIC. I think I can give you something interesting to watch.”