Hammer and Anvil
“Did you hear that?”
Commander Li Wei, captain of the Chinese People’s Liberation Army Navy Yuan-class submarine, twisted the corner of his mouth into a smug smile.
“It sounded like a scream, as if a block of steel were cracking open.”
“So the South Korean bastards really did burn out already, after all that talk about a new engine.”
Thinking back to the sound the sonar operator had just reported, Li Wei muttered with certainty in his voice.
Bearing 272, roughly 14 kilometers away.
The roar that had come from that direction was unmistakable proof of a mechanical failure.
“Captain, there’s a South Korean Navy rescue ship on the surface. It’s an ATS-II, Tongyeong-class. It’s sweeping the area with sonar pings.”
“Ignore it.”
Li Wei snorted.
“What are those rescue-ship scraps going to do, try to find us with sonar? Maintain depth at 80 meters. We’ll slip beneath the thermal layer.”
The ocean had a layer where the temperature changed abruptly with depth.
That difference in temperature bent and reflected sound waves, creating a vast wall of noise.
And if you hid beneath it, a surface ship’s sonar became useless.
Of course, a modern escort frigate or destroyer built specifically for submarine hunting might still be able to find them by dropping a variable-depth sonar, or a towed array sonar, below the thermal layer.
But the Tongyeong floating above them was nothing more than a rescue vessel relying on a fixed hull-mounted sonar.
A simple sonar ping firing straight down from above could never punch through the wall of refraction the sea itself created.
Their silent eyes would be bounced helplessly away around the 80-meter mark, that much was certain.
“Their own noise will help hide us. We’ll go in like shadows, take only the sound signature of the broken Korean submarine, and disappear. All we have to do is slip away without being seen.”
He had no doubt at all that he was carrying out a perfect covert infiltration.
He had no idea that, 14 kilometers away in the dark depths, someone was already watching him.
* * *
[Enemy vessel, distance 13 kilometers. Depth 80 meters. Covert approach beneath the thermal layer. Speed 5 knots.]
The Kim Gu’s CIC was as quiet as a temple, but on the monitors, a fierce war of information was unfolding.
“So they are crawling under the thermal layer after all,” I said, watching the situation with Captain Choi.
Until only a short while ago, when we had been moving at a slow speed, life aboard a submarine had seemed brutally dull.
But the moment I heard there was a Chinese submarine out there, I felt my dopamine spike like crazy.
Everything I saw and heard here, everything I experienced, felt new and exhilarating.
I turned my gaze toward Captain Choi.
He seemed just as entertained as I was, chuckling softly to himself.
“They probably have no idea we’re watching them. They’ll think our noise disappeared because we shut down the engine.”
“Because the noise our ship makes is only around 95 dB?”
“Exactly.”
In the sea, when you combined the sound of ideal waves, currents colliding, other large and small vessels, and marine life, the ambient noise of the ocean always hovered around 95 dB.
If a submarine’s noise matched that 95 dB level, or was even quieter, then an enemy submarine far away simply couldn’t hear it.
In effect, the enemy had their eyes and ears covered, thrusting their blade forward without even knowing where we were.
But.
Not everything about the situation was satisfying.
“Everything’s fine, except for one thing—I’m a little worried about communications. If we want to really humiliate those bastards, we need to coordinate with the Tongyeong floating right above us.”
“Ah. The Tongyeong is moving with us?”
“Yes. Right now it’s probably tracking our movement from the surface, about one kilometer away. Sonar operator, can you locate the Tongyeong?”
“It’s proceeding at 10 knots from bearing 115.”
While taking in the sonar operator’s report with Captain Choi, I nodded.
Choi was frowning.
“The Chinese submarine is approaching at 5 knots. At that speed, its sonar sensitivity will be at its best. If we use ordinary underwater communications to talk to the Tongyeong, they’ll pick us up immediately. But we can’t fail to coordinate either… tsk.”
“Underwater communications?”
When I asked, Choi answered without taking his eyes off the monitor.
“It’s a method of direct communication using sound waves. But because it uses low frequencies, the sound spreads in all directions. If we use it now, it would be the same as advertising our position to the Chinese submarine.”
“I see.”
I nodded.
The Chinese submarine was 14 kilometers away.
Even that far, the sound waves from underwater communications would still reach an enemy submarine.
So yes, that method was out.
“Is there any other way?”
“We could rise close to the surface, launch a communication buoy, or extend a mast. Then we could use satellite or data link. But if we deploy a buoy with an enemy ship this close, the fluid noise from cutting through the water will give us away for sure.”
There was deep regret in Choi’s voice.
A textbook answer, true to military doctrine.
Submarine communications always wore the chains of stealth.
“Hmm.”
I rubbed my chin, thinking.
Right now, the Kim Gu was proceeding quietly, with no notable noise after the problem that had cropped up in the stern earlier.
If we could keep that state and coordinate with the Tongyeong moving above us, we’d be able to mess with the Chinese submarine properly.
But to do that, we needed a way to communicate with the Tongyeong.
A way to make our intentions clear without being detected by the Chinese submarine.
After a moment’s thought, I asked, “Captain. What if we have communications set the modem to an ultra-high frequency band?”
Choi looked mildly troubled.
“Ultra-high frequency? That’s not suitable for underwater communication. The wavelength is too short; it attenuates almost immediately in water.”
“That’s exactly what I’m after.”
“Pardon?”
“It won’t travel far, but its directionality is excellent. I want to turn that weakness around.”
I pointed at the communication console.
“The latest acoustic modem installed on the Kim Gu uses a phased-array method. If the communications operator raises the frequency band into the high range and narrows the sound’s beam angle so it fires only vertically, it should be possible, shouldn’t it?”
As he listened to my explanation, Choi’s eyes changed ever so slightly.
“The Tongyeong is on the surface one kilometer away, and on the opposite side from the Chinese submarine. The Tongyeong is ahead of us, and the Chinese submarine is behind. If we send a high-frequency signal toward the Tongyeong, it’ll penetrate that one kilometer and strike her hull, but for the bastards coming in from 14 kilometers away, it’ll be absorbed by the seawater and vanish completely before it ever reaches them.”
“...Sonar operator. What do you think?”
After thinking it over for a moment, Choi asked.
The sonar operator, who had been listening with his headset lowered while Choi and I talked, said, “It makes sense. In my view, the Chinese submarine will not be able to detect the high-frequency signal sent in the opposite direction.”
“Hmm… is that so?”
Choi thought for another ten seconds or so, then drew a small breath.
Then he looked at me with a strangely impressed expression.
“Still... the engineer’s perspective is frighteningly practical. Very well. Communications! Set it up exactly as you just heard. Keep the message short. ‘Hammer and anvil.’ Send it.”
Crack.
A brief, razor-thin burst of data—so short that no human ear could possibly hear it—shot up from the Kim Gu’s bridge.
It was a perfectly secure communication.
* * *
The bridge of the Tongyeong, a South Korean Navy rescue ship.
The sonar petty officer pressed his headset tight to his ears and shouted, “Captain! Ciphered transmission from the Kim Gu! It says, ‘Hammer and anvil’!”
The Tongyeong’s captain set down his coffee cup with a smirk.
“So they’re asking us to set the board for them... I get it. Fine, let’s pretend to be idiots.”
He turned to the helmsman and the sonar operator and gave his orders.
“Fire the ping. But sweep the wrong places on purpose. Make the rhythm sloppy too. Let’s wander around like we’ve got no idea where they are.”
“Haha. Yes, sir!”
Clang... clang...!
The Tongyeong’s sonar ping spread through the sea.
Like a drunk man shining a flashlight at random, the Tongyeong was carefully missing the place where the Chinese submarine was lurking.
* * *
A little later, once the Chinese submarine had approached the middle of the thermal layer.
“See?”
Li Wei sneered at the sonar display.
“That’s the level of the South Koreans. We’re right above their heads, and they’re still blundering around in the wrong direction.”
The Tongyeong’s pings came in irregularly, drifting farther and farther away.
Li Wei relaxed.
“The rescue ship lost us. We move in now.”
The wolf stepped willingly toward the trap.
Deeper into the jaws waiting open for it—the jaws the Kim Gu had been holding in reserve.
And not long after that.
Clang—!!
Clang—!!!
Suddenly, a high-powered active ping slammed straight down from above and shook the sea.
The sound had plunged in from the surface and passed so close to the submarine that it felt like it had brushed against the hull.
“S-starboard side, about 30 meters! Their ping just skimmed past us!”
The sonar operator screamed in shock.
“That wasn’t some sloppy miss! They’re aiming directly at us!”
As if to prove his point, active pinging began to ring out from all directions.
Piiiiing—!
Fweeeeeeet—!
The terrifyingly clear, high-pitched sound reverberated along the hull, as though a giant steel bead were scraping across it with a metallic grind.
Listening to those sounds, Li Wei frowned in irritation.
The crew watched him anxiously.
“Don’t look so worried. We just got caught at a bad moment. Rapid dive to 150 meters. We’ll head down somewhere safe.”
“Depth 150 meters, rapid dive!”
The best way to escape a surface ship’s detection range was to go deeper.
Repeating the order, the helmsman began maneuvering the hull.
Feeling the submarine tilt quickly, Li Wei crossed his arms and closed his eyes.
Then, with practiced balance, he calculated the situation in his head.
However many ways he ran the numbers, the situation did not seem all that bad.
The Korean submarine is broken, and the surface ship is firing off pings to protect it... We still have the initiative.
All they had to do was stay hidden from the enemy surface ship deep in the sea, cut behind the Korean submarine while it searched for a chance to escape with its engines off.
Then they would secure the sound signature, toy with the enemy a little, and return to China with ease.
That was what he was thinking as they reached 150 meters.
Li Wei said to the sonar operator, “Sonar, report.”
“...The surrounding area is quiet. The Korean surface ship remains silent. It seems to be concentrating on finding us.”
“And the Korean submarine?”
“Silent.”
“I see. So that’s how it is.”
Feeling his nerves ease, Li Wei rubbed his forehead.
How much longer would they need to spend here?
Since the Korean submarine was on a trial run, it couldn’t endure for long.
Within ten hours or so, it would probably be unable to hold out any longer and would start making noise in order to tail off and retreat.
It was common sense that a diesel/AIP submarine with a problem in its propulsion system couldn’t just endure indefinitely underwater.
“For now, everyone should rest a little. Reduce engine output and maintain silent running so you can get some recovery in.”
“...Haa.”
At Li Wei’s words, the crew’s taut nerves instantly slackened.
Sighs of relief rose from every direction, and a few men even collapsed back into their seats.
Li Wei watched the scene, then was just about to take his seat in the captain’s chair when—
Eeeeeiiiing……
Hoooooo……
Inside Li Wei’s submarine, a grotesque sound suddenly echoed from outside the hull.
It wasn’t mechanical, and it was nothing like the sound of water being sliced apart.
It sounded like some deep-sea creature wailing, or a woman sobbing underwater.
“...?!”
The Chinese sonar operator’s eyes trembled violently beneath his headset.
Li Wei, who had just been trying to settle back into the captain’s chair and enjoy a moment of relief, also lurched to his feet in shock at the sound traveling through the hull.
“Sonar! What the hell is that?!”
“S-something seems to be attached to the stern!”
The sonar operator shouted in a voice that was almost a scream.
Li Wei’s expression hardened.
“Is it the propeller?”
“No! It’s not the propeller! It sounds like a ghost! There’s nothing on sonar!”
The faces of the crew, who had only just begun to regain their composure, quickly went pale.
An unknown cry echoing from the other side of the pitch-black sea.
It was an unmistakably terrifying situation.
“Where is the Korean submarine?! Can’t you hear anything at all?!”
Li Wei shouted desperately.
The sonar operator answered, on the verge of tears, “Nothing! I can’t hear anything at all! Only this weird sound!”
Li Wei felt cold sweat trickling down his spine.
The Korean side was absurdly quiet.
And then, this eerie sound too.
A dangerous fragment flashed through his mind.
Then could it be... that even the huge roar from earlier was part of a trap set by the Korean submarine?
Had they detected the approach in advance and deliberately lured them in?
Li Wei’s face began to twist with dawning alarm.
What if the new Korean submarine was quieter than anything he had imagined?
What if they were using it to lure them in, while the surface ship waited above them with a trap already set?
Then they were being toyed with completely.
In the worst case, the South Korean Navy might even tighten the pressure and force them to surface.
If this dragged on, South Korean surface ships would swarm in, and they might be dragged up from the water in the middle of enemy territory in utter humiliation.
Dangerous.
Unless this turned into an actual wartime incident, nobody would die or be sunk—but his career could still be finished outright.
Worse, the crew’s careers might be ruined too, simply because they had been aboard the same ship as him.
“...”
Li Wei clenched his fist.
Then, doing his best to ignore the thunderous noise that still kept ringing out, he approached the helmsman in a low voice.
“Increase engine output. Very slowly, smoothly. We’re getting out of here. Don’t provoke them.”
“...Understood, Captain.”
The helmsman carefully moved the control wheel.
As the hull began to shift little by little, Li Wei felt a drop of cold sweat run down his cheek.
His back was already soaked through with it.
They had to slip away like thieves.
He had to calm the situation down somehow, quietly, without making trouble.
Thinking that, Li Wei prayed the South Koreans wouldn’t make another move.
But then—
“Depth charge drop! Enemy vessel is dropping depth charges!”
The sonar operator’s scream tore through the CIC.
Everyone there looked instinctively upward, toward the ceiling above their heads.
“Depth charges, for real?”
“No way, the South Korean Navy would actually use depth charges...?”
Right at that moment, while several crewmen were speaking in fear,
BOOM—!!!
An explosion rocked somewhere above them, and a faint tremor followed through the hull.
These were people who had swept through enemy waters in simulations but had never experienced real combat.
Some of the terrified crew began screaming.
“Depth charges!! They’re real depth charges!!”
“They attacked us! We’ve been exposed! We’re dead!”
“Everyone, calm down!”
Li Wei shouted at the panicking men.
“If they drop depth charges, that means war! Those are just underwater signal flares, you idiots! It’s a warning! They know exactly where we are and are telling us to come up—!”
The brief moment when Li Wei was trying to restore order.
Clang—!!
It wasn’t a sound.
It was a physical blow.
The shockwave from a high-powered active sonar blast fired at point-blank range struck the Chinese submarine’s hull like a hammer.
“Aaaagh!”
Li Wei and the crew writhed on the floor in agony, as if their eardrums were about to burst.
Explosions above them. Shockwaves behind them.
A perfect encirclement.
Li Wei’s mind went blank.
In the twenty years he had lived as a submarine sailor, he had never once faced a crisis this bad.
“Run!”
Li Wei screamed, crawling across the floor.
Pride and dignity could go to hell; first they had to survive.
“Launch decoys! All ahead full! Engines at maximum power! Get out of here, now!”
Shushushushuk—!
The Chinese submarine fired decoys like mad, as if its rear end had caught fire.
The screw spun like crazy, ready to burst apart, exposing the submarine’s distinct sound signature to every corner of the sea.
* * *
“Good grief... if they flee that noisily, what are they even doing? Don’t you think so, Director?”
“Haha, yes. They must have been in a real hurry.”
Kim Gu CIC.
While talking with Captain Choi, I clicked my tongue.
On the screen, every bit of data from the fleeing Chinese submarine was being recorded in ugly, embarrassing detail.
The sound pattern at top speed.
The unique frequencies of its decoys.
The vibration signature of the engines during hard acceleration.
Even the sound of the ballast tanks dumping water.
“They’re practically throwing a tantrum. We’ve gotten their sound signature cleanly now. Next time we hunt those bastards, I could shoot blindfolded.”
Watching the data displayed on the monitor, Choi said that, then suddenly seemed to recall something and turned toward me.
There was a strange look on his face.
“Honestly... you really are something.”
“Me?”
“I mean you, Director.”
“Out of nowhere?”
At my reaction, Choi laughed and shook his head.
“Not out of nowhere. I’ve played hide-and-seek against the Chinese bastards dozens of times over the last ten years, and this is the first time I’ve ever seen them get so thoroughly toyed with.”
“Is that... so?”
“Exactly. And while I was thinking it over during the hunt, there was one thing that was different from before.”
“That Baek Gunwoo is here. That’s it, right?”
Seo, who had been watching the situation in silence the whole time from CIC, spoke up.
Choi nodded.
“Exactly. Of course, the ADD and Solaris Ocean both did their best, but I think this only became possible because Director Baek came aboard and caught every one of the submarine’s little noises. Thank you.”
Choi spoke in an exquisitely formal tone.
The whole thing had become so ceremonious that I felt awkward and waved it off lightly.
“Hmm. In that case, can I charge you a little more for the labor?”
“Haha. Charge us as much as you like. The Ministry of National Defense will pay gladly. We’ll be submitting a report too.”
“...A report?”
“We think our Navy Headquarters should know exactly what Director Baek did aboard our submarine.”
Choi said that with a hearty laugh.
Seo, standing beside him, nodded with a contented expression.
* * *
Shortly after successfully completing the sea trial and returning to the shipyard, I packed my bags and stepped back onto land.
And then, just as I was feeling relieved that the voyage had ended safely, a familiar officer from Naval Operations Command, someone I had seen a few times before, approached me.
“Good afternoon, Director Baek. Would you mind sparing me a moment?”
“...Pardon? Out of the blue?”
“The Chief of Naval Operations has come down here personally to meet you.”
The Chief of Naval Operations?
To see me?
No, why?