I’ve been exploring an alternative submarine gameplay model based on an energy-limited high-speed concept, derived from a patented thermal cycle approach. Originally, this thermal cycle was developed for high-efficiency ground power generation, but I’ve found that it leads to some interesting implications when applied to underwater power and propulsion.
Instead of a submarine that can sustain high speed indefinitely, imagine something like this:
Capable of very high speed (around 45 knots) for Virginia size sub with ~50MW propulsion
But total high-speed usage is limited per mission (roughly ~36 hours equivalent@45 knots,or ~690 hours@10 knots)
Extremely quiet at low speed (battery / gas turbine closed-cycle operation)
Requires energy management rather than constant high-speed mobility
The gameplay loop would look something like:
Long periods of stealth and passive listening
Short bursts of high-speed repositioning (20–30 minutes)
Attack from a favorable position at lower speed
High-speed disengagement
Gradual loss of mobility as energy is consumed
In other words, less of an “always-fast hunter” and more of a timing-based predator.
From a technical perspective, this behavior can be supported by a closed-cycle gas turbine system using hydrogen as fuel (produced onboard via diesel autothermal reforming, ATR), liquid oxygen as oxidizer, and a bottoming cycle such as an Organic Rankine Cycle (ORC). The propulsion would be range-extended electric, with an overall system efficiency on the order of ~56%.
I’m happy to discuss the engineering aspects in more detail, but what I’m most interested in here is how this translates into gameplay.
Would this kind of energy-limited high-speed model be:
Interesting and tactically meaningful?
Too restrictive compared to nuclear submarines?
Worth exploring as an alternative playstyle?
Curious to hear your thoughts.
Energy-limited high-speed submarine gameplay – based on a patented thermal cycle
-
GasTurbineAIP
- Posts: 3
- Joined: Tue May 05, 2026 10:10 am
-
GasTurbineAIP
- Posts: 3
- Joined: Tue May 05, 2026 10:10 am
Re: Energy-limited high-speed submarine gameplay – based on a patented thermal cycle
The control room was calm and dimly lit, filled with the quiet glow of tactical displays and the low hum of onboard electronics.
Deep beneath the Pacific, the submarine moved silently under pure electric propulsion.
No turbine noise.
No cavitation.
Only darkness and silence.
Captain Walker stood behind the tactical table.
“Engineering status?”
The chief engineering officer glanced at his display.
“Battery SOC eighty-seven percent, sir.”
“How many ATR units are in thermal standby?”
“ATR Three and ATR Four in full hot standby. ATR One, Two, Five, Six, Seven and Eight in warm standby. No cold systems online.”
Walker nodded with quiet approval.
“Good. I don’t want cold ATRs inside the combat zone.”
“Aye, sir.”
“Maintain low-speed profile. Keep TB-34 deployed.”
The submarine continued gliding silently through the abyss.
Then—
**TORPEDO WARNING**
A sharp alarm shattered the silence.
Red lights flooded the control room.
“Torpedo transient detected! Bearing zero-eight-five! Range approximately ten nautical miles!”
The atmosphere transformed instantly.
Captain Walker reacted without hesitation.
“Deploy acoustic countermeasures! Emergency evasive maneuver, port fifteen degrees! Fire four torpedoes down probable bearing spread pattern!”
“Countermeasures away!”
“Torpedoes away!”
“Emergency retract TB-34!”
The hull tilted violently as the submarine began turning.
Walker’s voice remained calm and precise.
“Maximum sprint protocol. Bring all turbines online.”
“Emergency turbine startup initiated!”
The electrical officer shouted over the rising noise.
“Battery propulsion at maximum discharge! Estimated full-power battery endurance: 25 minutes!”
The submarine accelerated brutally.
12 knots.
18.
27.
34.
Deep inside the engineering compartments, dormant machinery began waking up.
“ATR Three and Four increasing oxygen feed!”
“Other ATRs entering rapid thermal ramp!”
“Hydrogen buffer tank pressure decreasing.”
“Gas turbine ignition sequence initiated across all units.”
A deep mechanical roar spread faintly through the hull — distant, muted, but unmistakable.
The sound resembled jet aircraft engines spooling up somewhere far inside the submarine.
The hull vibration intensified.
The sonar operator shouted:
“Enemy torpedo still tracking! Countermeasure separation successful!”
“Take her deeper,” Walker ordered. “Use the thermal layer.”
“Descending to six hundred meters!”
Outside the hull, seawater temperature continued dropping.
The submarine accelerated harder.
38 knots.
41.
42.
Engineering reported again:
“All eight turbines in startup sequence. Estimated five minutes to full-load operation.”
“LOX low flow rate to ATR and Gas turbine is maintained.”
“Hydrogen buffer pressure continuing to fall.”
Then—
45 knots.
“Total propulsion output approaching fifty megawatts.”
The entire hull groaned under the hydrodynamic stress.
Five minutes later:
“All eight gas turbines online and full speed at low load.”
“ATR thermal ramp still in progress.”
“Hydrogen buffer pressure continuing to decrease slowly”
The submarine continued descending into the freezing darkness at maximum speed.
The sonar operator’s voice remained tense.
“Enemy torpedo still inbound!”
Walker did not even look up.
“Maintain sprint.”
......
Twenty more minutes passed.
The submarine continued racing through the abyss at forty-five knots while the engineering systems stabilized step by step.
“ATR One online.”
“ATR Two online.”
“ATR Five through Eight now reaching full thermal state.”
“Hydrogen production increasing to full level.”
The electrical officer checked his display again.
“Battery SOC down to only eight percent.”
No one in the control room reacted.
Then finally:
“All eight ATR systems now at full-load operation.”
"All gas turbine now at full speed and FULL load!"
“Hydrogen production matching turbine consumption.”
“Buffer tank pressure stabilized.”
“LOX flow to ATR and Gas Turbine is normal.”
“ORC recovery loop stable.”
“Estimated sustained forty-five-knot endurance: approximately twenty-eight hours.”
The engineering officer finally exhaled.
“Full propulsion system stabilized.”
Only then did Walker slowly raise his hand.
“Reduce speed. Twelve knots.”
The control room froze for half a second.
“Sir?”
“We need our ears back.”
“Reducing speed to twelve knots.”
The violent vibration faded rapidly.
The submarine slowed.
45 knots.
34.
26.
18.
12.
“Prepare TB-34 deployment.”
“TB-34 deploying.”
The control room became quiet again as speed stabilized.
“All turbines remain at full output.”
“Battery charging initiated.”
“ATR systems maintaining full thermal state.”
“Hydrogen buffer pressure recovering.”
“ORC recovery loop stable.”
Outside the hull, the long towed array slowly streamed back into the freezing darkness behind the submarine.
“TB-34 deployment ninety percent complete.”
The sonar operators waited in tense silence.
Then suddenly—
“Torpedo contact regained!”
“Enemy weapon still inbound! Bearing unchanged!”
Walker instantly slammed his hand onto the tactical table.
“Emergency retract TB-34!”
“Full sprint again! Maximum power!”
“Diverting DC bus power to propulsion motors!”
“TB-34 emergency retract initiated!”
The submarine surged forward violently once more.
Even at maximum acceleration, the engineering status remained stable.
“All turbines remain at full load.”
“ATR network stable.”
“Hydrogen production matching consumption.”
“Battery charging halt”
The submarine tore through the deep ocean at forty-five knots once again but now on 8 x gas turbines-- special designed as semi-closed & intercooled/recuperative cycle burning hydrogen. The combustion product is water, which condenses inside the cooled exhaust duct and is then collected, processed, and stored onboard the submarine.
......
Twenty minutes later, the sonar operator finally spoke.
“Enemy torpedo acoustic signature fading rapidly.”
“Probable fuel exhaustion.”
Walker stared silently at the tactical display for several seconds.
Then calmly:
“Reduce speed to twelve knots.”
“Deploy TB-34.”
“Return to silent hunting profile.”
The submarine slowed gradually.
45 knots.
34.
24.
18.
12.
“TB-34 deployment complete.”
“Passive sonar returning to full sensitivity.”
“Battery charging continues.”
“ATR systems transitioning to cruise-load operation.”
“Hydrogen buffer being recovered.”
The control room returned to darkness and silence.
Somewhere behind them, the exhausted enemy torpedo drifted lifelessly into the abyss.
Captain Walker folded his arms.
“Now let’s find out who fired first.”
Deep beneath the Pacific, the submarine moved silently under pure electric propulsion.
No turbine noise.
No cavitation.
Only darkness and silence.
Captain Walker stood behind the tactical table.
“Engineering status?”
The chief engineering officer glanced at his display.
“Battery SOC eighty-seven percent, sir.”
“How many ATR units are in thermal standby?”
“ATR Three and ATR Four in full hot standby. ATR One, Two, Five, Six, Seven and Eight in warm standby. No cold systems online.”
Walker nodded with quiet approval.
“Good. I don’t want cold ATRs inside the combat zone.”
“Aye, sir.”
“Maintain low-speed profile. Keep TB-34 deployed.”
The submarine continued gliding silently through the abyss.
Then—
**TORPEDO WARNING**
A sharp alarm shattered the silence.
Red lights flooded the control room.
“Torpedo transient detected! Bearing zero-eight-five! Range approximately ten nautical miles!”
The atmosphere transformed instantly.
Captain Walker reacted without hesitation.
“Deploy acoustic countermeasures! Emergency evasive maneuver, port fifteen degrees! Fire four torpedoes down probable bearing spread pattern!”
“Countermeasures away!”
“Torpedoes away!”
“Emergency retract TB-34!”
The hull tilted violently as the submarine began turning.
Walker’s voice remained calm and precise.
“Maximum sprint protocol. Bring all turbines online.”
“Emergency turbine startup initiated!”
The electrical officer shouted over the rising noise.
“Battery propulsion at maximum discharge! Estimated full-power battery endurance: 25 minutes!”
The submarine accelerated brutally.
12 knots.
18.
27.
34.
Deep inside the engineering compartments, dormant machinery began waking up.
“ATR Three and Four increasing oxygen feed!”
“Other ATRs entering rapid thermal ramp!”
“Hydrogen buffer tank pressure decreasing.”
“Gas turbine ignition sequence initiated across all units.”
A deep mechanical roar spread faintly through the hull — distant, muted, but unmistakable.
The sound resembled jet aircraft engines spooling up somewhere far inside the submarine.
The hull vibration intensified.
The sonar operator shouted:
“Enemy torpedo still tracking! Countermeasure separation successful!”
“Take her deeper,” Walker ordered. “Use the thermal layer.”
“Descending to six hundred meters!”
Outside the hull, seawater temperature continued dropping.
The submarine accelerated harder.
38 knots.
41.
42.
Engineering reported again:
“All eight turbines in startup sequence. Estimated five minutes to full-load operation.”
“LOX low flow rate to ATR and Gas turbine is maintained.”
“Hydrogen buffer pressure continuing to fall.”
Then—
45 knots.
“Total propulsion output approaching fifty megawatts.”
The entire hull groaned under the hydrodynamic stress.
Five minutes later:
“All eight gas turbines online and full speed at low load.”
“ATR thermal ramp still in progress.”
“Hydrogen buffer pressure continuing to decrease slowly”
The submarine continued descending into the freezing darkness at maximum speed.
The sonar operator’s voice remained tense.
“Enemy torpedo still inbound!”
Walker did not even look up.
“Maintain sprint.”
......
Twenty more minutes passed.
The submarine continued racing through the abyss at forty-five knots while the engineering systems stabilized step by step.
“ATR One online.”
“ATR Two online.”
“ATR Five through Eight now reaching full thermal state.”
“Hydrogen production increasing to full level.”
The electrical officer checked his display again.
“Battery SOC down to only eight percent.”
No one in the control room reacted.
Then finally:
“All eight ATR systems now at full-load operation.”
"All gas turbine now at full speed and FULL load!"
“Hydrogen production matching turbine consumption.”
“Buffer tank pressure stabilized.”
“LOX flow to ATR and Gas Turbine is normal.”
“ORC recovery loop stable.”
“Estimated sustained forty-five-knot endurance: approximately twenty-eight hours.”
The engineering officer finally exhaled.
“Full propulsion system stabilized.”
Only then did Walker slowly raise his hand.
“Reduce speed. Twelve knots.”
The control room froze for half a second.
“Sir?”
“We need our ears back.”
“Reducing speed to twelve knots.”
The violent vibration faded rapidly.
The submarine slowed.
45 knots.
34.
26.
18.
12.
“Prepare TB-34 deployment.”
“TB-34 deploying.”
The control room became quiet again as speed stabilized.
“All turbines remain at full output.”
“Battery charging initiated.”
“ATR systems maintaining full thermal state.”
“Hydrogen buffer pressure recovering.”
“ORC recovery loop stable.”
Outside the hull, the long towed array slowly streamed back into the freezing darkness behind the submarine.
“TB-34 deployment ninety percent complete.”
The sonar operators waited in tense silence.
Then suddenly—
“Torpedo contact regained!”
“Enemy weapon still inbound! Bearing unchanged!”
Walker instantly slammed his hand onto the tactical table.
“Emergency retract TB-34!”
“Full sprint again! Maximum power!”
“Diverting DC bus power to propulsion motors!”
“TB-34 emergency retract initiated!”
The submarine surged forward violently once more.
Even at maximum acceleration, the engineering status remained stable.
“All turbines remain at full load.”
“ATR network stable.”
“Hydrogen production matching consumption.”
“Battery charging halt”
The submarine tore through the deep ocean at forty-five knots once again but now on 8 x gas turbines-- special designed as semi-closed & intercooled/recuperative cycle burning hydrogen. The combustion product is water, which condenses inside the cooled exhaust duct and is then collected, processed, and stored onboard the submarine.
......
Twenty minutes later, the sonar operator finally spoke.
“Enemy torpedo acoustic signature fading rapidly.”
“Probable fuel exhaustion.”
Walker stared silently at the tactical display for several seconds.
Then calmly:
“Reduce speed to twelve knots.”
“Deploy TB-34.”
“Return to silent hunting profile.”
The submarine slowed gradually.
45 knots.
34.
24.
18.
12.
“TB-34 deployment complete.”
“Passive sonar returning to full sensitivity.”
“Battery charging continues.”
“ATR systems transitioning to cruise-load operation.”
“Hydrogen buffer being recovered.”
The control room returned to darkness and silence.
Somewhere behind them, the exhausted enemy torpedo drifted lifelessly into the abyss.
Captain Walker folded his arms.
“Now let’s find out who fired first.”
Last edited by GasTurbineAIP on Thu May 07, 2026 2:57 am, edited 3 times in total.
-
GasTurbineAIP
- Posts: 3
- Joined: Tue May 05, 2026 10:10 am
Re: Energy-limited high-speed submarine gameplay – based on a patented thermal cycle
The submarine continued gliding silently through the deep Pacific at 12 knots.
Inside the control room, the tension had eased slightly, but nobody relaxed completely.
Captain Walker stood motionless beside the tactical display.
“Set course for the seabed ridge. Bearing one-seven-zero.”
“Aye, sir. New course set.”
The tactical officer looked up.
“Estimated arrival at ridge structure in fifty-three minutes.”
Walker nodded.
“Reduce propulsion load. Shut down four turbines.”
The engineering officer acknowledged immediately.
“Securing turbines Three, Four, Seven and Eight.”
Deep inside the engineering compartments, the roar of the gas turbines gradually softened as four units disconnected from the main propulsion bus.
“Propulsion demand reduced. One turbine now supplying cruise propulsion.”
“Remaining three turbines redirected to battery charging at ~20MW rate.”
“ATR systems reducing thermal output.”
“Hydrogen buffer pressure recovering.”
The electrical officer checked his display.
“Battery SOC recovering. Twelve percent… fourteen… sixteen.”
The submarine moved steadily through the darkness.
The massive underwater ridge slowly emerged ahead on the navigation display like a submerged mountain range.
Walker watched it carefully.
“Bring us close to the western cliff face.”
“Aye, sir.”
The submarine descended further, approaching the steep underwater wall.
Outside the hull, the ocean floor rose sharply into darkness.
The engineering officer reported again:
“Hydrogen buffer tank pressure restored to nominal combat reserve.”
“ATR output now matched to remaining turbine hydrogen consumption.”
The submarine settled into a quieter rhythm now.
No emergency acceleration.
No violent vibration.
Only the distant muted sound of flowing seawater around the hull.
Then the sonar operator quietly spoke.
“New acoustic contact.”
Everyone looked toward sonar.
“Active sonar. Surface combatant. Estimated range twenty-two nautical miles.”
A faint metallic ping echoed through the hull.
…Ping…
Several seconds later:
…Ping…
The sound grew gradually louder.
“Hostile destroyer closing.”
Another operator spoke:
“Additional airborne contact detected. Probable ASW helicopter.”
“Range?”
“Fifteen nautical miles. Dipping sonar patterns intermittent.”
The control room fell silent again.
The sonar display filled with distant echoes, thermal reflections and reverberations from the seabed terrain.
The destroyer’s active sonar pulses rolled through the underwater mountains like thunder.
…PING…
…PING…
Walker listened quietly.
But his eyes were not focused on the destroyer.
They remained fixed on the passive sonar display.
Finally he spoke.
“I’m less worried about their destroyer.”
Nobody answered.
Walker continued calmly:
“The destroyer wants us to hear it.”
Another sonar pulse echoed through the hull.
…PING…
He pointed toward the dark region beyond the ridge.
“The submarine behind them is the real hunter.”
The control room became completely still.
Walker stared silently at the tactical display for several more seconds before speaking again.
“When they first detected us, we were cruising at twelve knots.”
Nobody interrupted.
“If their submarine was tracking us passively before launch, then they were probably moving very slowly.”
The tactical officer slowly nodded.
“AIP boat?”
Walker answered quietly.
“Most likely. Five knots, maybe less. Pure battery propulsion.”
Another sonar pulse rolled through the hull.
…PING…
Walker’s eyes narrowed slightly.
“A boat like that can hear well. But it cannot run fast.”
Nobody spoke.
“Their Stirling engines don’t produce enough propulsion power for sustained pursuit.”
He pointed toward the tactical map showing the submarine’s previous sprint track.
“And if it’s a lithium battery boat instead, they still wouldn’t chase us at flank speed for an hour.”
The tactical officer nodded slowly.
“Battery depletion risk.”
“Exactly,” Walker replied.
“Even modern battery submarines have limits. Twenty knots, maybe a little more for short periods. But not forty-five.”
Another sonar pulse echoed through the underwater mountains.
…PING…
Walker folded his arms.
“We sprinted at forty-five knots for nearly an hour.”
He looked again toward the empty darkness behind them on the display.
“If my estimate is correct…”
He paused briefly.
“…there are probably no conventional AIP submarines anywhere near us now.”
Silence returned.
Walker studied the underwater terrain map carefully.
The steep cliff beside them rose almost vertically from the seabed.
The destroyer’s active sonar continued sweeping through the water above.
…PING…
…PING…
Walker finally spoke again.
“They may hear echoes from this cliff for hours.”
Nobody moved.
“At this depth, with this terrain, active sonar reflections will be everywhere.”
He pointed toward the cliff face beside the submarine.
“If we stop here and stay tight against the rock wall…”
Another sonar pulse rolled through the sea.
…PING…
“…their sonar may simply interpret us as part of the seabed.”
The sonar chief slowly nodded.
“Bottom clutter and multipath reflections.”
Walker gave a faint smile.
“Exactly.”
Then his voice became quiet again.
“But a passive submarine is different.”
The control room fell silent once more.
Walker looked into the darkness beyond the ridge.
“A smart submarine captain will ignore the loud echoes.”
Another distant ping echoed through the hull.
…PING…
“He will listen for the ocean itself changing.”
Nobody spoke.
Walker finally gave the next order.
“Stop the boat.”
For a moment, nobody moved.
Then:
“Stopping propulsion.”
“Speed decreasing.”
The remaining propulsion turbine disconnected from the propulsion bus.
The electric drive motors powered down.
“Battery charging complete.”
“All gas turbines secured.”
“LOX flow zero across all ATR systems.”
“ATR units transitioning to thermal standby.”
“Electrical heat maintenance active.”
“Hydrogen buffer pressure stable.”
The submarine drifted silently beside the underwater cliff face.
12 knots.
9.
5.
2.
Then—
Zero.
The submarine no longer felt like a vessel moving through the ocean.
It felt like part of the mountain itself.
Far away above them, the hostile destroyer’s active sonar continued sweeping the sea.
…PING…
…PING…
And somewhere beyond the noise, hidden in the darkness, another submarine was still listening.
Walker looked once more into the darkness beyond the ridge, listening to the distant active sonar pulses rolling through the ocean.
Then he spoke quietly:
“We begin silent ambush operations now. Thirty megawatt-hours of battery reserve is enough to keep us hidden here for a very long time.”
Inside the control room, the tension had eased slightly, but nobody relaxed completely.
Captain Walker stood motionless beside the tactical display.
“Set course for the seabed ridge. Bearing one-seven-zero.”
“Aye, sir. New course set.”
The tactical officer looked up.
“Estimated arrival at ridge structure in fifty-three minutes.”
Walker nodded.
“Reduce propulsion load. Shut down four turbines.”
The engineering officer acknowledged immediately.
“Securing turbines Three, Four, Seven and Eight.”
Deep inside the engineering compartments, the roar of the gas turbines gradually softened as four units disconnected from the main propulsion bus.
“Propulsion demand reduced. One turbine now supplying cruise propulsion.”
“Remaining three turbines redirected to battery charging at ~20MW rate.”
“ATR systems reducing thermal output.”
“Hydrogen buffer pressure recovering.”
The electrical officer checked his display.
“Battery SOC recovering. Twelve percent… fourteen… sixteen.”
The submarine moved steadily through the darkness.
The massive underwater ridge slowly emerged ahead on the navigation display like a submerged mountain range.
Walker watched it carefully.
“Bring us close to the western cliff face.”
“Aye, sir.”
The submarine descended further, approaching the steep underwater wall.
Outside the hull, the ocean floor rose sharply into darkness.
The engineering officer reported again:
“Hydrogen buffer tank pressure restored to nominal combat reserve.”
“ATR output now matched to remaining turbine hydrogen consumption.”
The submarine settled into a quieter rhythm now.
No emergency acceleration.
No violent vibration.
Only the distant muted sound of flowing seawater around the hull.
Then the sonar operator quietly spoke.
“New acoustic contact.”
Everyone looked toward sonar.
“Active sonar. Surface combatant. Estimated range twenty-two nautical miles.”
A faint metallic ping echoed through the hull.
…Ping…
Several seconds later:
…Ping…
The sound grew gradually louder.
“Hostile destroyer closing.”
Another operator spoke:
“Additional airborne contact detected. Probable ASW helicopter.”
“Range?”
“Fifteen nautical miles. Dipping sonar patterns intermittent.”
The control room fell silent again.
The sonar display filled with distant echoes, thermal reflections and reverberations from the seabed terrain.
The destroyer’s active sonar pulses rolled through the underwater mountains like thunder.
…PING…
…PING…
Walker listened quietly.
But his eyes were not focused on the destroyer.
They remained fixed on the passive sonar display.
Finally he spoke.
“I’m less worried about their destroyer.”
Nobody answered.
Walker continued calmly:
“The destroyer wants us to hear it.”
Another sonar pulse echoed through the hull.
…PING…
He pointed toward the dark region beyond the ridge.
“The submarine behind them is the real hunter.”
The control room became completely still.
Walker stared silently at the tactical display for several more seconds before speaking again.
“When they first detected us, we were cruising at twelve knots.”
Nobody interrupted.
“If their submarine was tracking us passively before launch, then they were probably moving very slowly.”
The tactical officer slowly nodded.
“AIP boat?”
Walker answered quietly.
“Most likely. Five knots, maybe less. Pure battery propulsion.”
Another sonar pulse rolled through the hull.
…PING…
Walker’s eyes narrowed slightly.
“A boat like that can hear well. But it cannot run fast.”
Nobody spoke.
“Their Stirling engines don’t produce enough propulsion power for sustained pursuit.”
He pointed toward the tactical map showing the submarine’s previous sprint track.
“And if it’s a lithium battery boat instead, they still wouldn’t chase us at flank speed for an hour.”
The tactical officer nodded slowly.
“Battery depletion risk.”
“Exactly,” Walker replied.
“Even modern battery submarines have limits. Twenty knots, maybe a little more for short periods. But not forty-five.”
Another sonar pulse echoed through the underwater mountains.
…PING…
Walker folded his arms.
“We sprinted at forty-five knots for nearly an hour.”
He looked again toward the empty darkness behind them on the display.
“If my estimate is correct…”
He paused briefly.
“…there are probably no conventional AIP submarines anywhere near us now.”
Silence returned.
Walker studied the underwater terrain map carefully.
The steep cliff beside them rose almost vertically from the seabed.
The destroyer’s active sonar continued sweeping through the water above.
…PING…
…PING…
Walker finally spoke again.
“They may hear echoes from this cliff for hours.”
Nobody moved.
“At this depth, with this terrain, active sonar reflections will be everywhere.”
He pointed toward the cliff face beside the submarine.
“If we stop here and stay tight against the rock wall…”
Another sonar pulse rolled through the sea.
…PING…
“…their sonar may simply interpret us as part of the seabed.”
The sonar chief slowly nodded.
“Bottom clutter and multipath reflections.”
Walker gave a faint smile.
“Exactly.”
Then his voice became quiet again.
“But a passive submarine is different.”
The control room fell silent once more.
Walker looked into the darkness beyond the ridge.
“A smart submarine captain will ignore the loud echoes.”
Another distant ping echoed through the hull.
…PING…
“He will listen for the ocean itself changing.”
Nobody spoke.
Walker finally gave the next order.
“Stop the boat.”
For a moment, nobody moved.
Then:
“Stopping propulsion.”
“Speed decreasing.”
The remaining propulsion turbine disconnected from the propulsion bus.
The electric drive motors powered down.
“Battery charging complete.”
“All gas turbines secured.”
“LOX flow zero across all ATR systems.”
“ATR units transitioning to thermal standby.”
“Electrical heat maintenance active.”
“Hydrogen buffer pressure stable.”
The submarine drifted silently beside the underwater cliff face.
12 knots.
9.
5.
2.
Then—
Zero.
The submarine no longer felt like a vessel moving through the ocean.
It felt like part of the mountain itself.
Far away above them, the hostile destroyer’s active sonar continued sweeping the sea.
…PING…
…PING…
And somewhere beyond the noise, hidden in the darkness, another submarine was still listening.
Walker looked once more into the darkness beyond the ridge, listening to the distant active sonar pulses rolling through the ocean.
Then he spoke quietly:
“We begin silent ambush operations now. Thirty megawatt-hours of battery reserve is enough to keep us hidden here for a very long time.”