Scorpion in the Sea

TWENTY-SIX

“Eight knots,” ordered the Captain. His forehead was damp with perspiration, and his uniform was getting sticky.

The depth gauge continued to hold steady; the whine of the pumps beneath the deckplates of the control room competed with the creaking and crackling noises coming from the pressure hull. The needle backed off to 129, and then 128.

“Get her level. Now. We need to turn.”

The Musaid continued to coach the planesman as he adjusted bow and stern planes to bring the boat level. As the water was forced out of the negative tank, the boat became more responsive.

“Come port to 040, small rudder angles,” ordered the Captain.

He knew that if he could bring the submarine’s heading around to a course perpendicular to the oncoming destroyer’s search axis, the net effect would be to nullify the doppler on any returning echoes, regardless of his speed. The tradeoff was that he would now present the whole length of the submarine to the probing sound rays, but he counted on depth and the swirling acoustic layers of the Stream to mask the larger target he presented.

“Depth unstable,” called the Musaid urgently, putting his hand on the helmsman’s shoulder to stay the turn order.

Turning without depth control could spell disaster because the planes would induce rolling moments. The Captain looked at the depth gauge needle; as it cycled between 128 and 130. The submarine was porpoising, creating a shallow roller coaster ride as her buoyancy changed. The pumps continued to mill and grind.

“Commence the turn! Now! I need to show him null doppler,” shouted the Captain.

The Musaid removed his hand, his face stiff.

“Helm, Aye. Commencing the turn,” responded the helmsman, his voice cracking. The other men in the control room were frozen in position, afraid to look at one another.

“Sonar, what is the destroyer doing?” demanded the Captain, his voice more under control.

“Sir, he continues to ping in omnidirectional mode; the bearing is beginning to draw right; I don’t think he—”

The sonar operator suddenly opened his headset away from his ears, and then reached forward to the console to make an adjustment on the audio volume. He did not have to tell the Captain or anyone else in the control room why: the drawn out, ringing sound of a powerful directional sound pulse was reverberating in the control room. The men looked nervously at one another, and swallowed. A second long ping. The men had to hold on as the submarine rolled to one side, and then the other, as the rudder took effect. The Captain’s face tightened.

“Prepare to release a decoy. Quickly.”

The Deputy jumped from his station at the plotting table, and opened an air valve to arm the starboard decoy tube. There was a small hiss of air as the firing chamber filled to 3000 psi.

“Decoy tube is armed, Sir.”

“Very well.”

Now, thought the Captain, they would have to wait. It all depended on how determined this enemy was. He did not know how long this destroyer had been out looking around the operating areas. They had returned from the mothership in the early hours of Thursday morning and detected the pinging as they closed in submerged from the Gulf Stream. He had to know if this destroyer was actually conducting a search or just out testing his sonar. When his sonar officer had run back through his tapes and determined that this was a sonar they had encountered before, the Captain became suspicious. This destroyer’s presence was no accident. He had determined to shadow it, staying outside the predicted sonar range but near enough to record the enemy destroyer’s search patterns on the passive plot, to learn his tactics, and to appraise his vigilance.

The Captain’s mind raced. Somehow this destroyer may have detected the Al Akrab. And he was sure enough that he had something other than a school of fish to switch to directional keying. The turn would nullify the doppler, but now the Al Akrab would present her full beam to the enemy sonar. Going deep and the swirling layers above them should take care of that. Should.

“Passing 070.”

“Depth is stable; we can slow,” declared the Musaid, straightening up.

“Slow to five knots; continue the turn to 040.”

“040, Aye. Passing 060.”

The Captain considered the timing of the decoy launch. The decoy was a miniature transponder. It was shaped like a tiny torpedo, three feet long and about four inches in diameter. It had an air driven propeller that would run for about three minutes. In the body of the decoy was a sonar receiver and an amplifier. At its nose was a miniature sonar transmitter. The decoy could detect the incoming sonar pulse from the destroyer’s sonar, match its frequency, introduce some slight doppler shift, and ping back at the destroyer. The destroyer’s sonar would see a solid echo since the decoy’s response, however muted, was always stronger than the faint, real echo from the submarine. The destroyer’s sonar tracking circuits would then lock on to the decoy, while the submarine stole away into the depths.

The key to success was the timing of the decoy launch: if the enemy was in firm contact, the decoy would show up as a second contact and be exposed as a decoy, thereby confirming the presence of a submarine. If the enemy sonar had lost contact, the decoy could trick the enemy operator into thinking he had regained contact. The Captain listened carefully to the directional ping.

“Passing 045; steadying on 040.”

His new course was almost seventy degrees off the original course, enough to strip off most of the doppler effect, but not so far north that he would emerge back out of the protective thermal layers of the Gulf Stream. The long pings were not so loud now. The Captain made his decision.

“Release the decoy!”

There was a relatively loud thump as the decoy was expelled into the depths, pointed behind and below them. They could not know precisely which way the decoy would go, only that it would begin to transpond after thirty seconds. The Captain stared at his watch.

“Speed ten knots,” he ordered when the thirty seconds was up.

He would make a dash to the northeast, while hopefully the destroyer would lock onto the decoy as it careened along to the southwest at random depths.

“Ten knots, aye.”

The boat surged forward perceptibly. The long pinging was still audible, but its frequency had changed. Everyone in the control room listened and waited. Then the pinging suddenly stopped.