Water entered the intake, was heated by power from an array of fuel cells, and squirted astern like the exhaust of a ramjet, which in effect the Manta was. The engineers were still tinkering with the craft's dynamics. Top speed was believed to be in excess of 100 knots, however. They hadn't pushed that particular design envelope very hard yet in the testing program. Hawking had only had the tough little delta-foil up to eighty knots.
The real advance, though, was in the use of negative buoyancy. Traditional submarines used ballast tanks to adjust their buoyancy, surfacing when the tanks were blown empty. The Manta did not have ballast tanks, however, and, like an aircraft, was heavier than the medium through which it "flew," remaining aloft by creating a difference in pressure between its upper and lower body surfaces. So long as it was moving at a speed of at least fifteen knots, the Manta flew; if it lost power or fell below that critical speed, it would sink… and somewhere in the dark and crushing depths below, it would be destroyed.
Hawking took some comfort from the knowledge that in an emergency his cockpit module could be ejected from the Manta, and that did possess the buoyancy necessary to take him to the surface.
How deep was the Manta's crush depth? That was still an unknown, though numbers cranked through NRaD's computers suggested that the hull — a fantastically tough composite of titanium and carbon weave— would withstand the pressures of depths down to a thousand meters. This afternoon, Hawking was deliberately testing those numbers. The bottom here off the southern coast of Oahu was about 820 meters down. He'd taken the Manta into a deep dive, allowing sensors planted along the hull to register the stresses they encountered.
At 810 meters—2,700 feet — the water pressure exceeded 1,200 psi — a full three-fifths of a ton squeezing down on each and every square inch of the Manta's hull.
Well, so far, so good. The hull was designed with a certain amount of give, actually becoming stronger as pressure increased. There was stress, yes… but it was nowhere near the red line yet. Affectionately, Hawking reached up and patted the curved surface of the canopy, inches above his head. Good girl. She was a sweet craft.
Outside the canopy it was the blackest of black nights. It might be mid-afternoon on the surface, but sunlight could not penetrate more than about a hundred feet through even the most crystalline of tropical ocean waters. Here, in the Abyss, it was night absolute. He had the forward light on, but there was nothing to illuminate here save flecks of muck like drifting stars, tumbling past the canopy.
It was an eerie and somewhat unsettling feeling. It felt like he was flying at night, with the drifting debris serving as a poor substitute for stars. And yet, inches above his head, over half a ton of water for every square inch of his body lay waiting, held back by the high-tech plastic of the low, bubble canopy. If the bubble gave way, he would be dead before his nerve endings had time to react to the blast of infalling water.
He checked his sonar. A transponder signal was giving him a steady, pulsing beat, three hundred meters away and slightly to the left. He pulled the yoke again, nudging it to port.
The Manta had been envisioned as the world's first fighter submarine — a one-man, maneuverable craft that could "fly" far and fast from the parent boat, reconnoiter approaches to ports or shallow waters, identify potentially hostile targets such as mines, undersea sensor arrays, or enemy submarines, and even kill those targets with the high-speed microtorpedoes she carried in her bow. Someday, such fighters might provide an aircraft carrier with ASW defense, or protect conventional submarines from enemy subs. For now, the program was testing the feasibility of deploying them out of the missile launch tubes on board a converted Ohio-class boomer… in a sense turning the Ohio into a submarine carrier.
Science fiction indeed.
The target was less than a hundred meters ahead. He still couldn't see a thing through the murk. All his light revealed was a gray and shapeless emptiness alive with dancing motes of crud.
The bottom warning sounded, and he pulled the fighter's nose up slightly, slowing her. He thought he could see a thicker texture to the gray now, ahead and below… but it was still almost impossible to make out what he was actually seeing.
And then, out of nowhere, a shadow emerged from the gray, a cliff towering above his tiny craft, to his left.
His jaw dropped. That's it! Incredible!
Slowing now to just below the speed necessary to stay level, he let the Manta drift along the cliff's side. Almost as an afterthought, he tapped the touch-screen controls, switching on his port lateral lights.
Details sprang into sharply shadowed relief… black metal coated in slime… antiaircraft guns pointed skyward from clumsy looking, antique mounts… stanchions and railings and even deck cleats clearly visible. Ahead and just above him, he could make out faded white letters and numerals painted five feet tall… the legend I-401.
He'd found her.
Hawking touched another point on the control screen, which set the portside automatic cameras running. He'd promised Dr. Henson he'd record the site if he found it.
Correction. When he found it. He was the best there was, and the Manta was pure magic. There'd never been the slightest doubt.
Well, the dive transponder had helped.
The Manta was drifting down past the hull of a true leviathan, a Japanese submarine sunk off the coast of Hawaii sixty-three years before.
And what a submarine! The I-400 class, designated Sensuikan Toku by the Imperial Japanese Navy, had been a monster in her day… four hundred feet long and forty high, with a displacement of 3,530 tons and a crew of 144. She was the largest submarine ever to sail the world's seas until the advent of the ballistic missile submarines of the 1960s. There'd been four of the monsters all together — the I-400 and I-401, plus two slightly smaller vessels, I-13 and I-14. Launched in 1944, they'd been incorporated into Submarine Squadron One, under the command of Captain Tatsunosuke Ariizumi.
Hawking had studied up on his target before making the dive. The I-401 was of special interest to him because she was, in fact, a submersible aircraft carrier, a radical concept that had, fortunately, entered the war too late to affect its outcome. I-400 and I-401 had each carried three disassembled M6A1 torpedo bombers, while the smaller I-13 and I-14 each had carried two.
The Japanese had called the Aichi floatplanes Seiran. Various authoritative sources Hawking had consulted translated the name as "Mountain Haze." Equally authoritative sources translated the name as "Storm from a Clear Sky."
His money was on Storm from a Clear Sky, an apt enough name for the sleek little aircraft, given the manner in which it was to have been used. The I-400 subs had fuel tanks capacious enough to give them a range of 37,500 miles — one and a half times around the world without refueling, and this ten years before the advent of the nuclear-powered Nautilus. The Imperial Japanese Navy strategic planners had considered using the Sensuikan Toku—the name simply meant "Special Submarine" — to stage air raids against San Francisco, New York, or Washington, D.C.
That would have been a nasty surprise in the final year of the war. "Air Raid, Pentagon… This is no drill…. "
Eventually, though, Vice Admiral Jisaburo Ozawa, Vice Chief of the IJN General Staff, had settled on a truly chilling concept, designated Operation PX. SubRon One's ten-plane armada would be employed to launch a biological warfare attack against U.S. population centers along the Pacific Coast, delivering "payloads" of rats and insects infected with bubonic plague, cholera, dengue fever, typhus, and other germ warfare agents developed and tested at the infamous General Ishi's medical laboratory at Harbin, in Manchuria.