Sharov shook off those thoughts. That was one problem with the new Lira system. There was time to think now, while the computer ran the search. Focus on the hunt, he thought to himself.
Looking out his left cabin window, he saw Red 50 in the distance mimicking his own helicopter’s motions, smoothly slowing and settling into a hover, then the transducer array appeared under the fuselage. It took about ten seconds for it to disappear below the water’s surface.
“Two separate Lamb Tail signals this time,” Sonar announced over the intercom. Petty officers Alvarez and Frederick fed the bearings from their UUVs in turn to the geoplot.
“Control, UCC. We’ve got two three-point fixes. The eastern helo doesn’t have a chance of picking up José, so you can angle him toward us as soon as they stop pinging. Walter’s course is good.”
Jerry paused to study the tactical display, and jumped out of his seat to inspect the paper plot. Then keying the switch, he said, “Control, UCC, the other helo to the northwest is not close to either UUV, but it’s closer to own ship. I recommend increasing speed on both UUVs to eight knots so we can get some sea room.”
Weiss’s voice responded only a moment later. “Concur. Increase UUV speed to eight knots.”
Cavanaugh actually understood what they were doing and why. Because of the modem’s limited range, they could only get so far away from the UUVs, so moving the remotes faster allowed them to close the distance between them and Carter. But what if the Russians heard the UUVs? He started whispering to Mitchell, then stopped himself in mid-word and began again in a normal voice. “Aren’t you worried about the helicopter sonars hearing the UUVs’ propeller noise?”
Jerry made a face, but shook his head. “No. We ran the numbers several times. Unless they’ve done something to dramatically increase the sonar’s sensitivity — and I mean a lot — we should be fine. Not only is the Lamb Tail not that sensitive, but between the shallow water and the ice chunks, this is a noisy environment. Also, the UUVs use a permanent magnet electric motor. Not as many moving parts to make noise.”
Cavanaugh could understand that. “And a three-point fix is accurate, right?”
“Yes, it does mean an accurate fix, but it should really be called a ‘three-bearing fix,’” Jerry apologized. “It means we have three sonar bearings to the source of the sound, one from Carter and one from each UUV, and that they all cross at the same point. Of course, you only need two bearings to get a fix, but the third one is nice to have. Three bearings won’t automatically give you a perfect fix, though. If the bearings are fuzzy, you can end up with a triangle, and all you know is that the source is somewhere inside.”
Novikov announced “No contacts” over the radio, which was really unnecessary. Obviously, he would have reported a sonar hit immediately. Sharov interpreted the transmission as “What next?”
This was why it was important to pay attention to the search. Assuming there was something to find, and Sharov always assumed there was something to be found, it was within a circle of uncertainty that was constantly expanding at the contact’s speed. It was likely the contact wasn’t moving all that fast or their passive sonar search would have heard it, but time wasted planning their next move meant a larger area to look in. Sharov posited a low speed for the intruder, no more than ten knots, but plugging that value into the formula for the area of a circle still meant that time was against him.
He had already decided what to do if they didn’t find anything with their current dip. Responding to Novikov’s transmission, he entered a new search axis into the Lira computer, and announced, “New axis is due north, double interval.”
Red 50 acknowledged with his customary two clicks on the microphone switch, and his helicopter peeled away. Perplexed, Migulov asked, “I can see the contact trying to go north. If he tries to evade west he’ll just get trapped against October Revolution Island. It’s too close. But why the double interval?”
Sharov smiled. “What if our underwater friend knew it would take five or ten minutes for us to respond? What if he sprinted for several minutes and then slowed to creep speed?”
His copilot responded, “And you’re hoping to catch up.”
“Or get ahead of him.”
Migulov shrugged. “At this point, one patch of water is as good as another.”
Sharov shook his head, disagreeing. “No, Lieutenant. I am looking for one very special patch.”
They reached the new dip points almost at the same time, and Sharov thought that the Lira system delayed Red 50’s dip until his Red 81 was also in position.
“Listening,” Lukin reported.
Lieutenant Ford was marking the time. “He’s probably dipping again,” he estimated.
“Concur,” Mitchell answered.
Cavanaugh reasoned, “That means he — I mean, they are listening for us now, before they start pinging again.”
Jerry nodded. “It’s likely, given the time between the first two active searches. That’s about how long it takes the helo to lower and listen first.”
“But we don’t know where they are.”
The commodore nodded again. “They only reveal their position when they ping. But we’re at creep speed, and remember the captain ordered ‘Ultra Quiet.’” Mitchell turned to Lieutenant Ford. “How close does a Lamb Tail have to be to hear Carter passively?”
Ford picked up and read from a clipboard. “In these conditions, with us creeping and at ultra quiet, four hundred yards for a fifty percent chance of detection. It’s theoretically possible out to about nine hundred, but beyond that, we’re lost in the ambient noise.”
“And if they go active?” Cavanaugh asked.
“Effective range? About 3,500 yards, but they could still get a sniff out to about 4,200,” Ford replied, reading from the clipboard.
Cavanaugh was surprised at the difference between the passive and active ranges. “That’s an impressive difference.”
“It’s really their best tool in this environment,” Ford remarked casually. “It isn’t affected as much by the ice noise, but the shallow water depth is to our advantage.”
The intercom announced, “Conn, Sonar, one… no, two active sonars bearing two eight six and zero eight four.”
Cavanaugh now knew to wait for the sonar cross bearings to figure out the dippers’ new location. It only took a moment for the computers and the human to plot the different bearings.
Jerry reacted while the civilian was still trying to understand the display. “Control, recommend immediate course change to two nine zero! Dead slow, and as deep as you dare go!”
Two nine zero was staring straight at the nearest dipping helicopter to Jimmy Carter. Then Cavanaugh saw the range: thirty-nine hundred yards. A biting shiver did laps up and down his spine.
The intercom answered with a simple “Concur,” and the deck tilted again, this time in more than one axis.
Jerry saw the civilian’s panicked expression, and spoke matter-of-factly, “The other one’s safely out of range, but that near one, he’s a problem.” He shrugged. “The turn will put us bow-on to the active sonar, so we will send back a smaller echo, but it also means we get closer to him. Sort of a game of chicken.”