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
