Running at 10 knots, a black shadow glided silently five hundred metres below the waves. Her instruments detected a surface force at maximum range. Immediately Cetus shut down her own active sonar systems. After a small course correction she began to reel out the passive sonar towed array. The hydrophones attached to the array began feeding signals directly to the on-board digital signal processor.
As she drew closer, Cetus began to register the faint signals of a cluster of surface ships. The signal processor collected all sound emissions, filtered out background noises and converted the remainder into digital signals. A huge database of previously recorded material was accessed to lookup a match and tag the source.
At that moment no less than 18 warships were registering: a mix of destroyers, frigates, re-fuelling tankers and an aircraft carrier. Cetus was unable to solve the puzzle why so many ships from different navies were in such close proximity. She had no way of knowing that she had just blundered into a joint exercise between US and NATO fleets.
The first ship to be identified was the HMS Illustrious, the UK’s only remaining aircraft carrier. The digital processor began to identify other ships: the Spanish frigate Adm Juan de Borbón, the German frigate FGS Lübeck, the US frigate USS Taylor and the Polish frigate ORP General K Pulaski.
By now Cetus had identified 11 ships. Like a computerised game of chess, the main battle computer on board mapped out their positions, bearings and speed. As each position was plotted, plans of attack were proposed, considered and rejected or retained for later evaluation.
In truth the computer made these plans out of habit because it was programmed to do so. But none of these targets were on its acquisition list. Nevertheless if any of them threatened Cetus it would know well in advance what counter measures it had to take and it could respond without hesitation.
Even as the signals continued to be filtered and processed, Cetus began to reel in her passive sonar array in preparation for flight or fight.
But Cetus’ main preoccupation was with a target much further north and it was programmed to avoid anything that got in the way. As the fleet was southeast bound Cetus made another course correction south-west in an attempt to avoid them completely. In doing so it failed to detect the last of three submarines assigned to protect the fleet. HMS Astute drew the ‘tail-end Charlie’ position, located four miles south and three miles behind the last frigate. Astute was the largest and deadliest hunter-killer submarine ever built. As long as a football pitch and as wide as a four lane motorway, the UK’s first stealth submarine made less noise under water than a baby dolphin. She was the lead ship of the Astute class of nuclear-powered attack submarines and she lay directly in the path of Cetus.
Cetus picked up the tiny noises made by cavitations of the Astute’s propeller and matched these on its database. Caught between the submarine and the tail end of the fleet, Cetus had run out of options. To add to her difficulty Cetus’ computers knew that Astute’s sonar was so sensitive that she could continue to follow Cetus for up to 3,000 nautical miles.
‘Ops controller! Passive has a new contact on a bearing of 165 degrees.’
On board the Astute Commander Roger Thwaite also knew the outstanding capabilities of his sonar equipment and could not understand how the new item had only just been detected. ‘Active ping!’ Thwaite commanded.
The Astute sent out a high power sonar signal radiating in all directions. Any sound reflected back would be picked up by the Astute’s computers and converted into a radar-type picture on the scope. But it was already too late.
As soon as Cetus heard the active ping its own computer systems went into attack mode. On-board computers had already powered up the sonic cannon to low power and the sub aligned itself in advance of its target. Rather like a sportsman on a clay pigeon shoot, Cetus needed to aim in front of the target. Sound waves from its weapon were surprisingly slow in traversing the dense water of the Atlantic. If Cetus didn’t compensate, by the time they arrived the target would have moved on. The computer systems ensured that by using the technique of ‘leading’ the beam in front of the direction of travel, the deadly sound waves would connect with the target.
The impact of the sonic waves pounding on Astute’s hull created a noise like the sound of a jet aircraft taking off in the room. Loose articles on tables fizzed and jumped about, spilling to the floor.
‘Sir!’ called out the Ship Control. ‘After plane controls are becoming hard to handle! Initiating Emergency Operating Procedure.’
The commander acknowledged. ‘Petty Officer, issue ear muffs!’
Petty officer Saunders opened a cupboard and started distributing headsets to everyone in the control centre. While they didn’t block out all of the sound energy, it protected ear drums from pain and possible rupture. Commander Thwaite began calling out evasion manoeuvres to shake off the attack.
‘Rudder jamming!’ called out the second helmsman.
The volume of noise in the confined space rose again.
‘Sir’ the Chief Petty Officer shouted. ‘Reports from junior ratings in the bunk section. Nearly all are suffering from bleeding from the ears.’
Thwaite turned to his XO. ‘Any ideas about the source of the attack Smithy?’
Executive Officer Smith shook his head. ‘I think it’s time to leave.’
‘Action stations!’ Thwaite ordered immediately. ‘Surface, surface, surface!’ If the hull was breached he wanted to give his men the best opportunity they could to escape.
Above all the noise and confusion came a huge ‘whump’ of an explosion that rolled up and down the narrow gangways of the Astute. Glass smashed in some of the gauges and men were thrown off their feet. Thwaite clung to his chair while asking all sections for damage reports. Many of the seamen were overpowered by the explosion, noise and vibration to report anything meaningful.
‘Hull intact — so far!’ shouted the watch leader.
As HMS Astute powered towards the surface, the senior sonar rating thumbed his mike. ‘Commander, sonar. We have contact bearing 162 degrees. Unable to identify source.’
‘Torpedo room, prepare tubes one and two. Open the outer doors!’ the Commander snapped.
Another huge ‘whump’ crashed through the steelwork and smoke started to pour into the control room.
‘Fire torpedoes one and two!’
‘Torpedoes away and clear!’ The report from the torpedo room was drowned out by a cry from his executive officer.
‘Hull breeched! We are taking on water!’ yelled the XO.
‘Blow main tanks’ the Commander shouted above the din.
The submarine rocked as another explosion ripped through the close confines of the boat.
Chapter 15
The shock wave from the torpedo explosion radiated outward from the centre like an expanding ball. Cetus had little time to manoeuvre or prepare but it managed to face the wave front before it engulfed the submarine.
The effect on Cetus was similar to being hit on the nose: it was slammed back and the aftershocks buffeted it further. Its sonar receptors would have been damaged beyond repair if the overload protection circuit hadn’t kicked in and shut them down the instant before the compression wave hit.
Cetus recovered quickly and re-balanced its sonar sensitivity. Somewhere out in the darkness another torpedo was homing in.
Fifty milliseconds later Cetus boosted power to its electric engine and called the evasion package for another course change. The operating systems driving Cetus acted in full defensive mode. It determined the sub needed to put as much distance between itself and the source of the threat. The preferred course took it directly into the path of the previous explosion, saving it from certain extinction.