“Status, weps?”
“Tubes one through six ready for launch, targets locked in on visual and sonar. Did you want to confirm range with the laser?”
“No, it could give us away. Five seconds, gentlemen,” Chu said.
The three carriers were now easily made out at 24X.
“Ship Control, take us down to depth twenty-six meters.”
“Twenty-six meters, aye.”
“Three, two, one… tube one swimout!”
“Tube one enabled in swimout mode, sir, and tube one is clear. Bow camera indicates weapon one away.”
“Tube two swimout.”
“Two enabled, swimout mode, camera indicates weapon away.”
The launch sequence continued until the first six Nagasaki II torpedoes quietly left the ship, two en route to each aircraft carrier.
A kilometer from the Arctic Storm, several torpedoes slowly made their way to the aircraft carriers coming toward them, their passively listening sonars guiding them in. Over forty kilometers farther west, the two escort submarines cruised on at top speed, their sonars hearing nothing suspicious.
Weapon number one, the first launched from the bow of the Arctic Storm, plowed through the sea toward the approaching convoy. Its onboard computer — small and simple, yet of vastly superior power compared to the original Nagasaki design — computed the distance to the target and the target’s heading and speed. The weapon was driving toward a point in space where its speed would cause its track to intersect the carrier’s. It was guided in mid-flight by a nose-cone sonar array, the front of the weapon a flat-panel cover over the transducer.
Initially the weapon sonar was programmed to be passive listen-only, in receive mode. Pinging was rarely to be allowed, only if the unit lost its target in passive mode, but the target was so loud ahead that losing it would be impossible. The four massive screws of the target aircraft carrier thrashed loudly in the sea, coming from exactly the same bearing the weapon expected to hear it.
According to the computer model of launching platform, ocean, and target position, the weapon calculated that it was halfway to the target. It had been set by the launching tube to “immediate enable” mode, meaning it was allowed to detonate at any time after leaving the tube rather than being required to count out a distance from the firing ship. Fully armed, the warhead was warmed up, awaiting only for the initial low-explosive charge to detonate.
Aft of the nose-cone-mounted sonar transducer electronic package but forward of the onboard computer hardware was a ring around the torpedo skin linked to several redundant electronic modules making up the hull-proximity sensors. One sensor was magnetic, feeling the lines of the earth’s magnetic force, which were evenly spaced through the sea, but tremendously focused by the huge iron mass of a ship, a target. The magnetic sensors saw the distant spacing of the magnetic lines of force as white light and the gathering together of many lines of force, focused by the ship mass, as darkness on a white field. When the electronic module saw a dark spot of increased magnetism, they fed a positive signal to the computer’s warhead-detonation software. The second sensor was a wideband optical sensor, looking outward to the sea and able to sense the darkness below and the light above from the surface; a dark surface ship’s hull caused a positive signal to the detonator. The third sensor was a blue laser, shining outward in all directions to the sea, able to sense the presence of something that was not water or surface reflection. To it a hull stood out in stark contrast to the rest of the environment.
For the surface-ship-target mode, the torpedo had enabled the magnetic proximity sensor and the blue laser, with confirmation coming from the less reliable visual sensor. The software wanted to see a “hard detect” on magnetic or a definite laser sighting, confirmed by optics if possible. The optics could be fooled by a sudden cloud obstructing the sun, and were fooled at night by the phosphorescence of a ship’s wake. A laser detect absent a magnetic detection would be a valid detonation signal, since the weapon would assume that either the magnetic sensor had failed, or that an antimagnetic anomaly device was in use. This was a new torpedo countermeasure employed by warships to alter the magnetic field surrounding the ship, a device that was only modestly successful.
The weapon sped on at low-approach speed, 60 clicks, putting out its 186 hertz tonal into the water and emitting broadband white noise at 83 decibels relative to the ocean’s background noise, in the 50-decibel range. A broadband white-noise receiver would have picked out the weapon from a distance of ten kilometers. The 186 tonal sound-pressure level was emitted at 78 decibels, and would appear on the typical narrowband receiver at a distance of 30 kilometers. But the nearest broadband receiver was in the sonar dome of the destroyers behind the row of cruisers. The three aircraft carriers had no sonar systems, leaving that equipment to the cruiser, destroyer, and frigate hulls.
The second row of warships, the Aegis cruisers, had bow-mounted sonar domes configured for active pinging sonar rather than passive listening, and were capable of streaming a Dynacorp T-65 and T-148 towed sonar arrays, but the towed arrays were fragile and required clear sea miles astern, making the array unusable while steaming in a tight formation. The cruisers also were not using their active sonar domes, since the active sonar would interfere with the passive sonar searches of the 6881 submarines ahead.
In the third row behind the cruisers were the Aegis destroyers, which carried bow-mounted active sonars, all disengaged, and towed sonar arrays including the T-65, T-148, and T-22, all of which had been retracted and stowed for later use outside the battle formation. In addition, the destroyers carried a Seahawk V patrol helicopter with a dipping sonar transducer capable of active or passive sonar. The frigates behind the destroyers were similarly equipped, though the towed array systems varied. The only passive sonars engaged by the convoy were onboard the 6881 submarines, because a surface-ship sonar would hear so much broadband noise from the waves, hull flow, and screw that it would never hear an intruder submarine until it was within a fraction of a kilometer away. The surface ships counted on active pinging, when it was authorized, and a deep-running towed array that could dip far below the surface thermal layer, which kept noise from the surface channeled back to the surface and noise from the deep focused back deep. At the moment, though, these were uselessly stowed on large cable reels waiting for the ships to move to open water.
The passive-searching 6881s, far over the horizon on the other side of the Arctic Storm, were crippled by their distance from the torpedoes going the opposite direction and by the fact that they were facing west and the noise was due east. Their bow sonar spheres and wide-aperture hull arrays were not positioned to hear astern, and the propulsion noise from the reactor and turbine systems as well as the screw noise made detection of astern noises impossible in any case. Both 6881’s were equipped with rear-looking sonar systems in a towed teardrop array, but that rearview system was more of a self-defense mechanism, a last-resort warning of torpedo attack, rather than a sophisticated fleet defense sonar.
As the result of the poor deployment of the escort fleet’s antisubmarine-warfare equipment, six Mod II torpedoes sailed eastward undetected toward the hulls of the aircraft carriers.
The first-launched weapon sailed under the bow of the center aircraft carrier. Its proximity sensors, tuned to the most sensitive mode, detected the hull magnetic-force anomaly almost immediately. The optic module saw darkness above. The blue laser easily saw the hull, so close that it was less than a half torpedo-length away.