Deep Sound Channel (17 page)

"Good back support," he said.

"I want to work with Lieutenant Sessions on the Agulhas Current," Ilse said. "We'll have to head right through it and I can help."

"That's good," Jeffrey said. "Talk to the navigator too." "You give permission?"

"For sure," Jeffrey said, liking how she looked with that cap on. She'd bunched her hair up above the little plastic sizing strip at the back, making a kind of ponytail. "So far you'

ve been a real help, Ilse. Your enhancements to our models made a difference when we fought those Axis diesel subs. It's like having a sailing master aboard, twenty-firstcentury style."

"You mean the guy who advised the captain in the old men-o'-war?"

"Yeah," Jeffrey said. "Currents, soundings, weather, tides, wooden ships and iron men." Ilse smiled. "Was he part of the crew?"

"Warrant officer."

"What's that mean?"

"It's like being a noncommissioned officer, like a master chief, but you're more senior. Your pay and privileges are in line with a lieutenant maybe, even a lieutenant commander." Ilse seemed to like that.

"Can I follow you around while you get ready for your watch?"

"A little tour?" Jeffrey said.

Ilse nodded.

"Ready?" Jeffrey said.

"Yes."

"See," Jeffrey said, "the oncoming watch standers already took over, except for me."

"You always go last?" Ilse said.

"On this boat, yeah. The main thing's consistency." "Now what?" Ilse said.

"I'll take reports, starting with the helm."

"Sir," LTJG Meltzer said, "fly-by-wire ship control is rigged for nap-of-seafloor cruising, top speed twenty-six knots, general course now two one five, following route laid down by the navigator."

"Sir," COB said, "our depth is five two four zero feet, material condition ZEBRA, patrol quiet in the boat."

"Thanks, COB, Meltzer," Jeffrey said, then turned to Ilse. "I make up a watch bill every month. I try to mix people around now and then so all the crew can work together. But I also like to have the battle stations roster on duty often so they stay sharp as a group, not just at general quarters."

"Like now," Ilse said. "They're your lead-off team."

"Yup, the most experienced guys." Jeffrey sat down next to the off-going OOD at the command workstation. Jeffrey quickly skimmed the newest entries in the handwritten logbook, then spent more time on Captain Wilson's most recent instructions.

"Running as before, sir," the OOD said as Jeffrey finished. He was a junior officer from Engineering. "No new equipment casualties, no threats, all scheduled drills complete and satisfactory."

"Good," Jeffrey said. "Captain told me he was turning in."

"Yes, sir. Night orders are to go to modified ultraquiet at oh three hundred Zulu."

"I saw that, very well. . . . Next to fill me in, Ilse, shall be the navigating department."

"Sir," the senior chief on duty said, "we're driving south-southwest between the Soudan Bank to starboard and Rodrigues Ridge to port. Our position is 18 degrees 46.1 south, 60

degrees 14.4 east. Central Madagascar is six hundred miles off our starboard beam."

"Very well, Assistant Navigator," Jeffrey said. "Ilse, in older boats he'd be called the quartermaster."

Jeffrey brought up several displays on the command console one by one. "Now I'm taking a good look at the big picture in the boat. Pumps and valves and tankage lineup first, including filtration desalinators. . . . Air quality—we have radiacs and mass spectrometers for that."

Ilse nodded.

"Next," Jeffrey said, "is reactor and steam plant lineup and key-point pressures and temperatures. Look away for a minute, Ilse, this stuff is classified. . . . Then come loads on the turbogenerators and hydraulics. . . . And weapons status. See how you read the weapons board?"

"Little symbols," Ilse said. "Um, torpedo tubes, and, and missile silos?"

"We call that the vertical launch system, VLS, for our Tomahawk cruise missiles."

"How come so much is red?"

"Either we're too deep or fast to launch, or the weapon presets and firing solutions aren't loaded. Or we haven't flooded and opened the outer doors. The big Xs through the port torpedo tubes remind us they're inoperable now"

"This is great—it gives you everything at once. It's, like, idiot-proof."

"That's the idea." Jeffrey used the intercom to review secondary machinery status with the engineering officer of the watch, the EOOW. Satisfied, he hung up the mike.

"Challenger's a new ship," Jeffrey said. "The propulsion plant's still breaking in. Changes in key performance variables can give us hints of trouble. So far everything looks good."

Jeffrey stood and walked with Ilse the few paces to the sonar area. He peered at all the console screens.

"Morning, sir," Lieutenant Sessions said. "No nuclear detonations detected in this theater during the previous watch."

"A quiet night," Jeffrey said. "What's happening locally?"

"We have some neutral merchant shipping off our stern, sir. They'll be in our baffles soon but they're well distant and the range is opening fast. These submerged contacts here are biologic."

"Very well," Jeffrey said. "Sonar, I want you to get Ilse familiarized with our bottom nav and mapping capabilities. Pretend she's joined your division fresh from SUBSCHOL."

"Yes, sir," Sessions said.

Jeffrey glanced at a chronometer—it was 2326 Zulu. "Well," Jeffrey said, "now it's my turn."

Ilse thanked him and sat down next to Sessions. Jeffrey went back to the OOD. "I relieve you, sir."

"You have the conn," the OOD intoned, rising from the console.

"This is the XO," Jeffrey announced, "I have the

Conn.,,

"Aye aye, sir," the CACC watch standers said. The exOOD went aft. Jeffrey sat down and made some entries in the log, then settled into the command chair, grateful for the familiar routine of conning the ship. He was glad that for the next six hours the total concentration would relieve his mind of other things, including thoughts of Ilse Reebeck that weren't related to work.

"This gravimetry display is unbelievable," Ilse said.

"It's the closest thing to magic I've ever seen," Sessions said.

"It doesn't use stored data?" Ilse said, her eyes glued to the screen.

"Nope. It's completely independent of any database or our previous course or even the need to be moving. You just turn it on and there it is."

Ilse saw a crisp rendering of the seafloor terrain around the boat, contours and perspective drawn in by computer—a synthetic view as if she were peering through a window in the bow. Her other screen showed the corresponding bird's-eye view, looking down at Challenger. Ilse ignored all the numbers to the sides, course and speed and everything, riveted to this raw live imagery of the world outside the hull.

"What's the image resolution?" Ilse said.

"At short range," Sessions said, "better than ten meters."

"And it's all derived from local gravity?"

"Uh-huh," Sessions said. "Several groups of gradiometers and accelerometers throughout the boat. They measure changes in mass concentrations from different bearings."

"And this is all continuous motion," Ilse said, "in real time?"

"Yeah, the same thing COB and Meltzer have right now. It's refreshed every ten seconds."

"It must use lots of processing power."

"It's worth it," Sessions said. "We've got a hundred times the original Sea-wolf-class computer capabilities. The basic gravimeter math's nonclassified, but ours has special stuff civilian geologists don't know about."

"How new is this?"

"They were testing one on USS Memphis back in the late nineties at DEVRON

TWELVE, our squadron. That's what we do. We're operational SSNs and we also test technology and tactics, working with the Naval Underwater Systems Center in Rhode Island, and the various contractors."

Ilse stared at the terrain estimation display. "You can see right through things!"

"Sure," Sessions said. "Matter's transparent to gravity, right? One seamount shows up past another. Good thing too, else we couldn't go this fast so close to the bottom."

"You must use some kind of stored data as backup, don't you?"

"We do," Sessions said, "and to speed these calculations also. We have decent bottom charts, for gross verification and course plotting."

"You don't just feel your way?"

"Not usually. Hitting a basalt cliff head-on would be embarrassing."

"Yeah," Ilse said.

"The helm guys need to stay real sharp," Sessions

said. "At twenty-six knots we move one boat length every eight seconds. Watch this." On-screen Ilse could see that the canyon they'd been following took a sharp turn to the left. As if on cue to her thoughts the boat banked to port. She watched as Challenger followed the canyon leftward, still hugging the deep ravine's right wall, several hundred feet up. The boat leveled off as it came out of the turn.

"You can see why we don't stream a towed array," Sessions said.

"Neat," Ilse said. "But how come we don't stay right on the bottom?"

"Stealth. It's too obvious. If we follow one wall partway up, we still get all the benefits of terrain masking."

"And I guess that makes it tougher for the enemy to lie in ambush or plant a mine."

"You got it, Ilse. It also gives us more lateral clearance, room for turning sideways just in case. Right down on the canyon floor we'd be boxed in."

"Can you use this under ice?" Ilse said. "For ice avoidance?"

"Maybe someday," Sessions said. "It's great to fix your posit under the ice cap, update your inertial nav, since you can't just pop up for a GPS fix then, even in peacetime. Instead we orienteer from the gravimeter, based on distinctive bottom features and our charts. For ice avoidance we have to use our sail-mounted high-frequency sonar, which radiates and has short range and can't see past a bummock or berg. The problem with the gravimeter is the density gradient's not strong enough—rock or sediment versus water's one thing, but ice versus water's something else."

"Then what about detecting other subs? Or surface ships?"

"Smart question," Sessions said. "No good, unfortunately, is the answer. Floating surface units and submarines displace a mass of water equal to their weight, right? So unless you're really close, there's not enough change in the gravity field."

"What if you are close?" Ilse said.

"There's another problem if they're moving," Sessions said. "It adds a centripetal gradient that's unknown to the algorithms, not like own-ship velocity. And if you do know target range and course and speed, who needs the gravimeter?"

"What about a nuclear sub, though, one that's motionless or on the bottom? The reactor compartment must be extra heavy. Wouldn't that show up, compared to spaces full of air, as a mass field discontinuity?"

"Now you're getting into classified stuff," Sessions said. "But it's no secret gravimetry can help you avoid something man-made that's real heavy, like an oil drilling platform, since it doesn't move."

Ilse went back to her screens. Watching Challenger's swift progress through the benthic topography was fascinating. The boat followed an S-curve between underwater peaks, hard right and then hard left again. Ilse could see it coming, on the bird's-eye view, and she watched the other picture as they took the turns, like looking out the windshield of a car.

"I have another question," Ilse said, "if this isn't secret."

"Try me," Sessions said.

"I need to understand this to help you navigate. How come Jeffrey isn't giving orders?"

"You mean no helm commands?"

"Yeah. When we fought those diesel boats, Captain Wilson kept saying make your course this, make your depth that, hard right rudder. . . ."

"Nap-of-seafloor's different. That's one reason we have senior people at the helm. Commander Fuller can overrule them, even take control himself if need be from his console, but this is different from maneuvers near the surface. Here we follow the terrain."

"So our detailed course is a given," Ilse said. "Mother Nature calls the shots."

"Pretty much."

"Could you fight a battle this far down?"

"I suppose," Sessions said. "The enemy would have to find us first. Down here you get lost in the sonar grass, just like with radar, and even look-down acoustic Doppler, which tracks suspended particles, gets confused by multiple currents at different depths."

"So more depth means more protection?" Ilse said. "Yeah," Sessions said. "It's not just that you get more thermal and salinity layers to hide behind—"

"Plus the deep scattering layer too," Ilse said, "as schools of biologics migrate up and down the water column every day."

"That's right," Sessions said. "Anyway, the point is, if the enemy is sort of overhead, the spherical attenuation model holds. The intensity of our self-noise as received by the other guy goes down with the square of range, so ten times deeper means just one percent the signal strength."

"I should bone up on this stuff," Ilse said.

"You need to," Jeffrey interrupted. "There's a series of tutorials you can run on the computer, with homework problems and everything."

Ilse realized he'd been listening in. There really is no privacy on a submarine, she told herself. "Yes, Commander," she responded, slightly irked. "I'll look at the tutorials once I'm done with the gravimeter." Jeffrey turned back to his console. Ilse watched her screens again. She saw large boulders show up now and then. Probably from underwater landslides, from seismic activity she knew never really ceased. Sometimes she saw talus slopes, rubble built up over eons at the base of undersea escarpments.

"You can fiddle with the picture if you like," Sessions said. "Use your trackmarble to look ahead, or rotate the

presentation and see things from a different angle." He showed her how.

"This is fun," Ilse said. "But I have another question. With nap-of-seafloor, we're not too exposed, you know, to enemy sensors planted on the bottom?"

"Yes and no," Jeffrey butted in again. "That's why we use broken terrain, where it's hard to place a trip-wire grid and seafloor current eddies make for lots of false alarms. We'd avoid a smooth, flat open-ocean basin at all costs, for just that reason."