Scorpion in the Sea

TWENTY-FOUR

“Idiot!” hissed the Captain, bursting into the control room. “Reduce speed to four knots! At once!”

The alarmed watch officer relayed the order swiftly, and the boat quickly began to decelerate from the sudden burst of speed ordered only two minutes ago.

“Make your depth 120 meters; flood negative — we must get some more layers above us.”

The control room watch was tense, every man sitting upright in his chair. The Musaid, his face drawn and haggard, loomed over the planesman, coaching him softly as they worked to get the boat deeper without making any telltale noises. Any further telltale noises. The distant destroyer had changed its search pattern suddenly, and headed directly towards them. The Watch Officer had reacted by ordering a burst of speed to get away, followed by a depth change. Only then had he called the Captain, who was already on his way to the control room when he sensed the boat surging forward on the electric motors.

The Captain scanned the gauges swiftly. “Sonar, report.”

“Sir, the enemy destroyer is closing from the west; I hold him on the port quarter, but he’s drifting in and out of my baffles. His speed appears to be unchanged. He’s still in omni transmission mode, no frequency change. No new keying rate.”

The Deputy looked up from the sound plot at the back of the control room. “Bearings indicate he has altered his pattern of search; bearings have steadied.”

The Captain cursed again. They were on the battery, so engine noises were not the problem. Doppler was the problem. If the enemy sonar operator had suspected he had a real contact, and focused on it at the same time the Al Akrab increased speed, the audio on the destroyer’s sonar would have shown down doppler, and thereby, motion away from the destroyer. Doppler was one of the crucial classification cues; marine life rarely showed doppler. As soon as he had entered the control room, the Captain had taken the speed off, and dived deeper to get more acoustic layers of water between the boat and the destroyer.

“Range?”

“Estimate the range to be 12,000 yards; there is no way to tell if he is closing or not,” said the Deputy from the plotting table.

“Bearing 280. Steady bearing.”

The destroyer was coming their way. Something had attracted his attention. Much would depend on what the destroyer did with his sonar. The next clue would be if he went to directional keying, pumping out all the acoustic energy in the direction of where he thought he might have a contact, rather than his present mode of banging out the ping in all directions.

“Sir, depth is passing through 70 meters. Negative tank is flooded.”

“Make your heading 110; speed five. Level off at 120 meters.”

“Planes, aye, 120 meters.”

The Musaid was trying to get the Captain’s attention. There was a distinct note of apprehension in the planesman’s voice. Three hundred and sixty feet was approaching the submarine’s extreme operational depth capability limit. The boat’s hull was already beginning to make small groaning and popping sounds as the steel hull compressed under the increasing pressure of the sea.

The Captain cursed again, silently. This was partly his own fault: he had ordered the watch officer to stay within five to ten miles of this destroyer ever since they had returned from the mothership and heard the steady pinging of a searching sonar. He glanced over at the Musaid, who looked swiftly at the rate of descent dial.

“100 meters; preparing to blow negative,” he said.

“No!” interjected the Captain. “Pump negative; increase speed if you must to hold her, but no noise. No air.”

The men controlling the dive scrambled to line up the valve manifolds. The negative tank, a large seawater ballast tank with oversized water-admission valves, sat astride the submarine’s center of gravity, and was used to make quick changes in the submarine’s buoyancy. Flooding the negative tank made the submarine immediately heavy, thus rapidly accelerating a diving maneuver. When the boat approached its ordered depth, the normal procedure was to force compressed air back into the tank and thus blow the seawater out, thereby quickly restoring the submarine’s neutral buoyancy. Depth was then maintained with careful use of the trim tanks, much like an airplane is trimmed up to stabilize flight once the climb to altitude has been completed.

The Captain was aware that the blast of compressed air from the flasks would send out a transmission of broadband noise. His order to pump out the negative tank with relatively silent electric pumps rather than using a blast of high pressure air was driven by the tactical necessity for silence. The price for silence was delay: pumping took much longer, especially against the pressure of almost 400 feet of depth. The delay, in turn, meant that the boat would settle past its ordered depth unless speed was increased so that she could be held at depth by the force of the water flowing over the forward and after planes.

“120 meters,” sang out the diving officer, his forehead glistening with sweat.

The hull was complaining audibly now, creaking and groaning throughout the boat. A fine mist had appeared in the air ventilating system, casting a thin aurora around the lights. The men in the control room tried hard to ignore the signs and sounds of the implacable grip of the deep.

“123 meters; I’m having trouble holding her. Request eight knots!”

“Eight knots,” replied the Captain.

His eyes, like those of every man in the control room, were fixed on the depth gauge. The black needle was inching around clockwise, past 125, 126, as the diving officer manipulated the bow and stern planes to put a shallow up angle on the boat, using the increased speed. The needle went to 127, and then to 128, as the boat mushed down into the depths. The boat inclined more sharply, and then levelled slightly. The diving officer had to take great care. He could put too large an up angle on the boat and cause it to stall like an airplane and even slip backwards. The key was to get the negative tank pumped out.

“We cannot hold her,” declared the Musaid softly. “You will have to blow negative.”

“No. Continue pumping. Ten knots.”

“Ten knots, aye.”

The depth gauge now indicated 130 meters, over four hundred feet of depth. The temperature was rising in the boat. At the back of the control room, a sailor surreptitiously closed the watertight hatch. The mist effect was more pronounced.

“Steady yourselves,” growled the Captain. “We have taken this boat to 170 meters before.”

He continued to watch the depth gauge; the needle was holding at 131 meters, as the extra speed took effect. His mind raced. The problem was now, once again, doppler. He could not maneuver the boat off the destroyer’s search axis until he had depth control back in hand, and the boat was now driving away from the enemy’s sonar at a speed which was definitely not typical of marine life. He desperately needed to make a turn.