One of the Sonar watchstanders shifted consoles, preparing to energize Pittsburgh’s High Frequency Array, the forward-looking under-ice sonar mounted in the front of Pittsburgh’s sail, used to detect ice formations ahead. The sonar technician entered the requisite commands, bringing the console on-line, then cast furtive glances at the ship’s Captain.
Buglione knew what he was thinking. Pittsburgh’s topsounder and Fathometer weren’t detectable, emitting narrow high-frequency beams that bounced back to Pittsburgh after reflecting off the ocean’s surface or bottom. But that wasn’t the case with the High Frequency Active sonar, which sent pulses out in front of the submarine — pulses that would likely be detected by the Russian submarine’s crew. Having set the Arctic Routine, Buglione had to make the decision he’d been putting off since Kazan turned north — whether to energize the under-ice sonar and risk detection.
He announced his decision. “Attention in Control. We will not use our under-ice sonar. We’ll let the Russians pick a path through the Marginal Ice Zone and follow directly behind.”
Buglione turned to the Helm. “Come left to course three-five-five.”
They had been trailing the Russian submarine with an offset to starboard, but needed to trail directly behind while in the Marginal Ice Zone.
After Pittsburgh eased into position behind Kazan, Buglione turned back to the north.
Moments later, the Quartermaster looked up from the electronic chart and announced, “Entering the Marginal Ice Zone.”
25
MARGINAL ICE ZONE
Inside the Marginal Ice Zone, Kazan maintained her steady trek north at ten knots while Plecas monitored the ice-detection sonar, topsounder, and bottomsounder. Thus far, the topsounder had detected only sporadic chunks of sea ice floating above them, while the bottomsounder reported the smooth, shallow bottom of the Barents Sea, which averaged only 230 meters in depth.
Plecas, however, was more interested in what the American submarine was doing. He glanced at the navigation table, which displayed the tracks followed by both submarines over the last day. The American crew had detected each of Kazan’s baffle clearance maneuvers and calculated its new courses and speeds exactly. They were well trained, which was not an unexpected revelation.
What was revealing was that the American submarine was matching Kazan’s movements exactly, mimicking them. That, combined with no high-frequency pings from the American submarine, indicated they were not using their under-ice sonar; they were relying on Kazan to show them the way.
Perfect.
As Plecas prepared to implement his plan, his thoughts shifted to his submarine’s ice-detection sonar. Objects in front of them would appear as a colored blotch, with different colors representing the intensity of the sonar return, with red indicating a large, deep, or dense formation. Unfortunately, ice-detection sonars weren’t very good at determining the depth of the object, which is what ultimately mattered. The color of the ice was the key. As Kazan closed on the object, shallow ice keels would recede upward and exit the top of the ice-detection beam. As it receded, the color would change from bright red to darker, cooler colors until it faded to black.
The ice-detection sonar used the submarine’s depth and a simple geometry algorithm to determine if the obstacle was a threat. If the ice didn’t change from red to another color within a certain distance — the Minimum Allowable Fade Range — it was deep enough to present a threat, and Plecas would have to turn or go deeper. The display was currently black; there were no ice formations ahead.
As Kazan continued north, small icebergs were sporadically detected, none deep enough to cause concern, until a bright red blotch appeared on the display, twenty degrees to starboard.
The ice-detection sonar operator announced, “Hold ice keel, bearing zero-two-zero, range twelve hundred meters.”
Plecas ordered, “Steersman, right standard rudder, steady course zero-two-zero.”
As the Steersman complied, Fedorov approached. “Captain, you’ve turned directly toward the iceberg.”
“I understand, First Officer.” Plecas said nothing more until Kazan steadied on her new course. He then ordered, “Steersman, ahead full.”
The Steersman rang up the new speed order, and Kazan surged toward the iceberg.
“Possible contact zig, Master one, due to upshift in frequency.”
Lieutenant Bob Martin, on watch as the Junior Officer of the Deck and head of the Section Tracking Party, made the report to Commander Buglione. While they were trailing another submarine, Buglione had augmented the normal watch stations with the Section Tracking Party, comprising an additional fire control technician to monitor the plots, a Contact Manager, and a Junior Officer of the Deck.
Martin moved behind the Plots Operator and examined the contact’s tonal on the display. After studying the frequency change and noting a right bearing drift, Martin announced, “Confirm target zig. Master one has turned to starboard. Set anchor range at five thousand yards.”
Shortly after Kazan steadied on her new course, the Plots Operator reported, “Possible contact zig, Master one, due to downshift in frequency. Contact is either turning away or increasing speed.”
The Section Tracking Party repeated their analysis, concluding Kazan had increased speed to twenty knots.
Buglione examined the new solution on the nearest combat control screen. A twenty-degree course change was understandable — perhaps they had detected an ice formation ahead. But why increase speed to twenty knots? Had they detected Pittsburgh, and were opening range in an attempt to lose them?
Pittsburgh needed to match Kazan’s speed, or they would lose contact.
“Helm, ahead full. Make turns for twenty knots.”
One thousand meters to iceberg.
Plecas remained focused on the ice-detection sonar display as the operator called out the distance to the iceberg.
“Captain, what are you doing?” Fedorov asked. “We will smash into the iceberg in ninety seconds if we do not maneuver.”
Plecas turned to his First Officer, answering Fedorov’s question with a question of his own. “How have the American crew’s tactics changed since we entered the Marginal Ice Zone?”
Fedorov answered, “Instead of following us with an offset to starboard, they are now directly behind us.”
“Why?”
“Because they are not operating their under-ice sonar, so they don’t give their presence away. They are using us to chart a safe path through the Marginal Ice Zone.”
“Exactly,” Plecas replied.
“I do not understand your plan,” Fedorov said. “I realize the American submarine will follow us toward the iceberg, but they will turn away at the same point we turn away, avoiding the iceberg as well. What will we have accomplished?”