by Joe Buff
"At least half a dozen to our one," Jeffrey said. "We only have three left now, so you'd think they'd start to run low too, even fresh from reprovisioning at the bluff."
"That's the whole point," Ilse said. "Jan's making sure we know he's there, somewhere in front of us, and
taunting us by visibly wasting ammo. He's messing with our minds."
2 HOURS LATER
Ilse and Jeffrey were grabbing a quick bite in the enlisted mess, visiting with the crew, released from general quarters a few at a time so they'd be in top form later. Bell had the conn again and knew where Jeffrey was.
One man finished eating, then lit a cigarette. Ilse bummed one off him—she didn't smoke but really needed one right now. She took a deep draft and then the both of them exhaled, blowing toward the overhead.
She saw Jeffrey give her and the crewman a funny look.
"Sorry, sir," the crewman said, "I'll put it out."
"What?" Jeffrey said. "Oh, no, no, that's okay. It's just that, urn, uh, you two gave me an idea." Jeffrey seemed to stare off into space. "Yeah," he said, "this just might work."
"What just might work?" Ilse said.
"It'll take a lot of careful effort," Jeffrey said, "and luck. Heavy-duty calculations, Ilse, using every bit of data that you've got. Conditions have to be perfect, and the whole thing might backfire. . . . Hmmm. . . . We might not have the vertical directivity to filter out the noise, and there might be too much Doppler distortion along the line of bearing."
"What are you talking about?" Ilse said, trying to stifle her annoyance, reminding herself Jeffrey was acting captain of the ship.
Jeffrey looked at her and grinned like a little boy. "I'll explain it on the way." He stood up. "To the sonar consoles!"
"You said there were hydrothermal vents around the choke point," Jeffrey said as they rushed down the nar-
row, bending companionway and past some enlisted berthing spaces.
"That's right," Ilse said.
"Active ones?"
"Yes."
"They give off heat, right?" Jeffrey said.
"Of course."
"And they spew dissolved minerals."
"That's what makes black smokers smoke," Ilse said. "Sulfides and sulfates precipitating when the superheated water meets the ice-cold ambient ocean."
"The precipitation builds up to make the chimneys," Jeffrey said.
"And it feeds the archaea and the tube worms," Ilse said.
"But it doesn't all precipitate out, right? Some stays dissolved?"
"Sure," Ilse said as they went up a steep ladder. "You can detect trace chemicals miles away sometimes, like helium 3."
"So the water isn't only hotter," Jeffrey said, "it has greater mineral content, like having higher salinity." "Yeah. So?"
"Don't you see?" Jeffrey said. "Horizontal and vertical thermoclines and haloclines, in the megaplume above a vent!"
"Oh," Ilse said. "I, I do see what you're getting at. . . . Acoustic lensing."
"Right," Jeffrey said. "Sound refracts away from water with higher speed and toward water with lower speed, and higher temperature and more dissolved minerals both mean higher speed. Each vent plume acts like a concave lens. It makes sound rays diverge."
"Urn . . . I concur."
"And they occur in fields," Jeffrey said, "the vents do."
"Sometimes," Ilse said.
"If you have two vents near each other, the place between them acts like a convex lens, like in a magnifying glass."
"I guess that's true," Ilse said as they reached the CACC.
"Sonar superiority," Jeffrey said. "With lenses we can make a telescope."
1 HOUR LATER
Jeffrey checked the gravimeter again. Challenger was following the side of a long escarpment on the east edge of a caldera, a huge bowl of volcanic origin.
"Torpedo in the water at our depth!" Sessions hissed. "Bearing three five nine, drawing left to right and closing, an inbound spiral course of unknown origin!"
"Range?" Jeffrey said, his heart pounding now.
"Bow sphere contact only! Signal strength implies about ten thousand yards, approach speed seventy knots!"
"Right in our face," Jeffrey said. "No data for a snap shot at Voortrekker, and if we turn away, we just make a better sonar target for that fish."
"Concur, sir," Bell said.
"Countermeasures and AT rockets are useless this far down," Jeffrey said. "Their exhausts are strangled by the pressure."
"Decoys and UUVs won't function either, sir," Bell said. "They'd implode right in the tubes the minute we equalize."
"Phone Talker," Jeffrey said, "quiet collision alarm." "Quiet collision alarm, aye, sir."
"Helm," Jeffrey said, "all stop." He didn't wait for Meltzer's answer. "Fire Control, make tube three ready
in all respects including opening outer door. Set lowest yield, dot zero one KT. Ter Horst might not know our range, so swim the unit out."
"Dot zero one KT," Bell said, "and swim the unit out."
"Tube three," Jeffrey said, "firing point procedures on the incoming torpedo. Intercept and detonate the unit through the wire. Match sonar bearings and shoot."
"Set!" Bell said. "Stand by. . . . Fire! Tube three fired electrically."
"Unit is running normally," Sessions said.
"Chief of the Watch," Jeffrey said, "stationary dive, rate of descent five hundred feet per minute."
"Stationary dive, aye," COB said, "five hundred feet per minute, aye. No maximum depth specified."
"Time to weapon intercept?" Jeffrey said.
"Two minutes," Bell said.
"How did he find us?" Jeffrey said.
"I don't know, Captain," Bell said.
Jeffrey eyed the displays. Do a one-eighty at the base of the escarpment and run back into God knows what? Voortrekker could easily have another torpedo lurking there. Turn to starboard instead, course 270, into the caldera that went far down past Challenger's crush depth? Rise and head to port and wind up naked against the escarpment crest, a dead setup for another shot? Ter Horst chose his ambush well. How did he find us?
"Helm," Jeffrey said, "the moment our unit detonates go to ahead full smartly, then use hard right rudder."
"Upon detonation go to ahead full smartly hard right rudder, aye."
"Course, Captain?" Bell said.
"Two seven zero and follow the bottom." The caldera. "Sir," COB said.
"Yes," Jeffrey said, "but it's the last thing he'll expect and he'll lose us in the reverb from these slopes."
Jeffrey saw Bell punch the button to fire the warhead.
The cataclysmic shock broke fluorescent light bulbs everywhere. Something threw Challenger backward and pressed her down.
"That explosion was too strong," Jeffrey said. "They must have detonated the torpedo as our own weapon came up to it."
"Confirmed!" Bell shouted. "Our unit did not detonate!" "Clever bastards," Jeffrey said.
"Maneuvering acknowledges ahead full smartly!" Meltzer said. "My rudder is hard right!"
Challenger banked to starboard.
A reverberating shock wave hit and the starboard list grew sharper. The boat put on a nasty forward trim.
"Sir," COB shouted, "our depth is fifteen thousand feet!"
"Sir," Meltzer yelled, "we're in a snap roll from that reverb catching the sail! Without bowplanes I do not have control of the boat!"
"Helm," Jeffrey said, "disengage fly-by-wire and work manually on hydraulic backup.
Try to get us out of this uncoordinated turn."
"Understood," Meltzer said.
"Sir," COB said as he helped Meltzer, "our hull's so compressed we're losing buoyancy.
I'm having trouble compensating even with the pumps lined up in series."
Before Jeffrey could answer there was a crackling crunch from all around, then a nonstructural weld in the port-side CACC bulkhead snapped.
"We're squashing inward," Jeffrey said. The depth gauge showed 15,200
feet. The pressure gauge showed 450 atmospheres. "If we do an EMBT hydrazine blow now, it'll take forever to work and we'll be helpless once it does, a sitting duck."
"Sir," the phone talker said, "torpedo room reports heavy misting round the tube eight door repairs." At this
depth, Jeffrey knew, the bilge pumps couldn't possibly keep up with a major leak, and at this depth any leak was major.
"Captain," Ilse shouted. "Look at the gravimeter!" Jeffrey saw the image on his screen, the wall of the
escarpment. It was shimmering, starting to give way. "It's an underwater landslide!" Ilse said.
"Helm," Jeffrey said. "Ahead flank smartly, full rise on the diveplane functions." The forward trim amounted to a twenty-five-degree down-bubble.
"Ahead flank smartly, aye," Meltzer said. "Full rise on the diveplane functions, aye." He flicked the engine-order dial with one hand while he pulled back on his control wheel with the other and then turned it, his face grimacing in concentration. "Maneuvering acknowledges ahead flank smartly."
The depth gauge showed 15,400 feet. The gravimeter showed a gap in the escarpment, growing into a vicious gouge—it couldn't track the moving boulders, it just showed their effect.
"Sir," COB said, "soundings are eighteen thousand feet!"
"Acknowledged," Jeffrey said. Deep enough to die. "A seismic sea wave's coming any second from the avalanche!" Ilse yelled.
The depth gauge showed 15,600 feet. The hull groaned again and the ESM room bulkhead started warping against the overhead. Dust from crumpled insulation fell on Ilse and the sonar people.
A terrible roaring shove struck the ship and the inclinometer went to forty-two degrees starboard list. Fifteen thousand eight hundred feet.
"Sounds like we buried them alive," Van Gelder said, "before Challenger's torpedo could intercept our unit." "Mmph," ter Horst said. "I wouldn't entirely count on that. Serves me right for trying to not be too profligate with our weapons expenditure. . .
. Sonar, any contact on the target?"
"Negative, sir," the sonar chief said. "Conditions are impossible."
"Very well," ter Horst said. "Number One, detonate the other nuclear torpedo."
"Detonate the unit from tube two, aye aye," Van Gelder said.
Ter Horst waited till they heard the distant blast, dulled by the intervening escarpment wall. "Now then," he said, "if we can't hear them, they certainly can't hear us. Helm, set maximum revolutions, steer one six zero."
"Set maximum revolutions, aye aye, sir," the helmsman said, "steer one six zero, aye aye. . . . Turbine room answers steam throttles are wide open, sir."
"We'll head directly to the choke point now," ter Horst said. "It should take us three hours. We'll wait for Wilson there, after we string the last of our deployable hydrophone line beyond the bases of the seamounts on both flanks of the hump."
"Understood," Van Gelder said.
"Eventually," ter Horst said, "if we don't make contact, we'll come back here and use our bottom-penetrating sonar to locate their reactor compartment under all that rock. One way or another the verge of the Prince Edward Fracture will be Challenger's final hunting ground."
Another atomic detonation went off harshly somewhere past Challenger's starboard quarter. The force of it was amplified and drawn out by the backstop of the escarpment wall, and the gravimeter showed another huge section starting to give way. Above it all Jeffrey heard a snap, and water sprayed into the passageway forward of the ship control station.
"It's just freshwater," COB said, bypassing the rup-
ture while he tried to do three other things at once. There was computer hardware near that pipe but nothing shorted out.
"It couldn't stand the flexing and the shock," Jeffrey said. "Our sea pipes are much stronger but something's gotta give." The huge main steam condenser cooling loops—vital to the propulsion system's thermodynamic cycle—were made of a different ceramic composite than the hull, designed to withstand intense pressure from within—shear instead of strain—but only up to a point. Challenger's hull openings were her weak spots, like in any submarine.
The gravimeter showed a giant avalanche now, and another seismic sea wave caught the ship.
"Sir," Meltzer said, "we're at sixteen thousand feet! I cannot get a positive angle of attack!" More moaning crunching sounded and the deck began to warp.
"Very well, Helm," Jeffrey said. "Planing out of the dive just isn't working fast enough.
All stop, stop the shaft."
"All stop, aye!" Meltzer said. "Maneuvering acknowledges all stop! Stop the shaft, aye!
Maneuvering acknowledges stop the shaft!"
"If we need bowplanes," Jeffrey said, "we'll move in reverse. The sternplanes will become our bowplanesthey're much bigger and they'll have even more bite from the propulsor wash when going backward."
"Understood," Meltzer said.
"Back full smartly," Jeffrey said.
"Back full smartly, aye! . . . Maneuvering acknowledges back full smartly!"
"Be real careful," Jeffrey said, "this evolution makes us very unstable. One more seismic sea wave will be the end of us."
"Acknowledged!" Meltzer said.
Jeffrey eyed the gravimeter, praying hard against more landslides. "And try to get us on an even keel before we crash into that cliff."
1 HOUR LATE R
"That's just what I was afraid of, Ilse," Jeffrey said, looking at the imagery off one of her CD-RW disks, the outflow from a hydrothermal vent she'd once studied in detail.
Sessions nodded. "There'll be massive Doppler distortion along the line of sight, sir, and constant rippling of the acoustic image in the perpendicular plane."
The three of them stared at the picture on Sessions' sonar console.
"Here's a thought," Ilse said. "We could do what astronomers do to deal with atmospheric turbulence. Active adaptive optics, except electronically. It's really the same problem."
"But we need a known bright reference star for that," Jeffrey said, "or the equivalent, and this all has to work continuously in real time."
"That's what I mean," Ilse said. "What if we emit an active sonar beam, one that's directionally very tight, at minimum power? Wave it back and forth and grab the micro-
echoes off the precipitation particles? That would give a picture of water motion in the megaplume."
"Sounds great in theory," Jeffrey said.
"We'd have to work the wide-aperture system as a phased-array antenna," Sessions said,
"then digest all that raw data and reassemble everything for a sharply focused picture. . . .
And that's just to use this telescope thing on one line of bearing." Sessions turned to Jeffrey. "I don't know, sir."
"We'll use finite elements for approximation," Jeffrey said. "The processes are chaotic but they're spatially continuous."
"That's true," Ilse said. "The functions would be differentiable, mathematically."
"We can do a narrowband search to simplify things," Jeffrey said. "Even if Voortrekker auto-hovers so their reactor pumps and the rest of the propulsion plant are quiet, they need a bunch of megawatts to run all their
computers and their listening gear, and to keep their bow sphere warmed up for active melee ranging once the engagement starts. We'll listen for five-hundred-hertz tonals from their turbogenerators, and fifty-hertz sympathetic line hum. That'll help us filter out irrelevant noise impinging on our hydrophones."
"I concur," Sessions said. "The problem isn't writing the code to do all that, Captain. The systems administrator and his staff have been on it for a while already. They're boilerplating and building from tool kits with the commercial off-the-shelf software we have on board. The problem is running everything fast enough for the lens effect to work."
"We'll have to make as much space as we can inside our processors," Jeffrey said, "dump or switch off everything we don't need on the LAN, other programs, irrelevant data, pieces of the operating system even."
"Can you
do that?" Ilse said.
"We have off-line double backups," Sessions said. "It'll be a ton of work to reinstall everything later."
"If we don't do this," Jeffrey said, "or it doesn't work, there might not be a later."
"Deployable hydrophone lines are both in place," Van Gelder said. "Ship is in auto-hover. Tubes one through eight are loaded with deep-capable nuclear torpedoes, all warhead yields preset to one kiloton."
"I want to take us closer to the bottom," ter Horst said. "Around here sound rays trend upward, since sound speed increases with depth. That'll put us in a shadow zone against another terrain-hugging boat."
"I concur," Van Gelder said. "It's one benefit of being so deep in the isothermal layer."
He eyed a depth gauge. "Recommend we drop to forty-seven hundred and fifty meters, Captain."
"Helm," ter Horst said, "on auto-hover, stationary
dive, make your depth forty-seven hundred fifty meters."
The helmsman acknowledged.
"All deployable hydrophones are nominal, Captain," Van Gelder said, watching his sonar repeaters. "Our search plan focuses on sixty hertz and four hundred hertz, the base-line and high-frequency tonals of the American's dual-source AC electrical supply."
"Excellent, Number One," ter Horst said. "Now we wait, and listen."
Jeffrey and Ilse watched the live imagery from the ice-avoidance low-light-level TV
mounted on the sail. The plumes in the vent field to Challenger's front gave off faint luminescence, from the life-forms they fed and from chemical processes. The scalding water sprayed up from the chimneys, roiling black, spreading and mixing as it rose, the turbulence gradually subsiding with distance and elevation.
The sound of the large vent field came over the sonar speakers, rumbling and roaring like so many volcanoes or atomic bombs. Sessions filtered out the worst of the noise, which originated beneath the ocean floor or at the chimney mouths themselves. Commodore Morse looked on, kibitzing and offering moral support.
"My map of this field may be stale," Ilse said. "Sometimes a new smoker opens or an older vent dies off."
"From what we can see, your plot's accurate," Jeffrey said. "These two big plumes further in should give us a good objective lens."
