"Up in the bow of the sub, there's this big fiberglass sphere twelve feet in diameter, with hydrophones all over it. The chamber's filled with water, so it listens in on everything going on in the sea around us." He pointed at the waterfall display. "We get a visual readout here. Loud noises make a brighter point of light… like that one." He pointed to a slanting line across the screen.
"So what's that?"
"Sierra Two-seven-niner. A skimmer."
"Skimmer?"
"To a submariner, everything on the surface is a skimmer. Two-seven-niner is a supertanker leaving the Gulf. Bearing… zero-five-eight."
"Yeah? What's the range?"
Caswell made a face. "That's Hollywood. With sonar, you can get an accurate bearing on the target, but not the range. It's not like radar."
"Oh, yeah. They went over that when I had my indoctrination. To get range, you have to move the sub around."
"Right. That lets you triangulate on the target. The chief of the sonar watch can even request that the captain change course, just so we can get a better look at the target."
"So… how do you know it's a tanker?"
"That's my job," Dobbs said. "I'm using narrowband here. Right now we're towing a narrowband sonar array behind the Ohio," Dobbs explained. "The BQR-15. It picks up the same sound the broadband does, but feeds it through a computer, our narrowband processor. That sorts through the hash and zeroes in on what we call tonals."
"Tonals?"
"Yessir. Every ship and sub is filled with machinery, and most of it is making noise, one way or another. The screws. Seawater pumps. Turbines. Diesel engines. Every piece of machinery that rotates puts tonals into the water. And the processor can pick 'em out and match 'em to known sounds." He pointed at his display, which showed an oscilloscopelike line of light with a sharp spike in it. "When there's machinery in the area, that's what it shows us."
"That's the tanker again?"
"Yup. Her screws, actually."
Caswell had fallen silent. He was listening now, very, very intently. "Hey, Dobbs?" he said. "You might want to try fifty Hertz."
"Yeah? Whatcha got?"
"I'm not sure. I just thought for a moment… " Dobbs turned a dial on his console. "Jesus!"
"What is it?" Hawking asked.
"I think we have a bandit." Dobbs hit the intercom switch. "Con, Sonar! New contact, Sierra Two-eight-one! Bearing zero-four-five! Fifty Hertz tonals! I think it's a sub!"
"So what's all the fuss about fifty Hertz?"
"Quiet, sir!" Caswell said, his voice a harsh whisper. "Please!"
"Western electrical systems run on an AC frequency of sixty Hertz, Commander," Dobbs said quietly. "Russians run their equipment on a frequency of fifty
Hertz."
"That's a Russian sub out there?"
"Russian… or a boat purchased from them by one of their clients. Or maybe built to Russian specs. I do know one thing."
"What's that?"
"It ain't one of ours."
Chief Sommersby, the senior sonar tech, entered the room. "Let me have a listen," he said, putting on headphones. For a long moment he was silent. Then, "Control Room, Sonar. Recommend change of course to clear our baffles."
"Sonar, Control Room. Very well."
"Clearing out baffles?" Hawking asked. He sounded bewildered.
"I think we have several potential hostiles out there," Sommersby said. "We're getting lots of tonals, and they're consistent with Kilo-class submarines… and those new Iranian Ghadir-class boats. Trouble is, they're real, real quiet. Getting a fix on them is going to be tough. The big danger is that we have one trailing us astern. Can't hear for shit back there, because of the disturbance from our own wake. I just asked the skipper to bring us around in a big circle, which lets us listen to what's going on behind us."
"Contact!" Caswell said after several more minutes. "New contact, Sierra Two-eight-two, bearing one-one-two!"
"Ah-ha!" Sommersby said. "Nailed the bastard!"
"I've got him," Dobbs said. "Ghadir-class. He had his nose up our ass!"
"How do you know it's a Ghadir?" Hawking asked, staring at the new electronic spike that had just appeared on Dobbs' screen. The young aviator was clearly becoming more and more bewildered.
"Several weeks ago one of our L.A.-class boats spent some time following Iranian subs in and out of port," Sommersby explained. "Got some great beneath-the-hull photos through the periscope, and also recorded every sound they made. They picked up the tonals from the screw, both the diesel and electric motors, seawater pumps, toilets in the head, even an ice cream maker in the galley. Then they beamed all the data back to Washington by satellite, and they, in turn, beamed it out to us." Swiveling in his chair, he patted a console behind him. "Now our narrowband processor knows exactly what to listen for when there's an Iranian sub in the area."
Caswell heard the conversation with some part of his brain, but his full attention was focused on what he was hearing over his headset, and what he was seeing on the waterfall. Two Iranian subs were out there, obviously stalking the Ohio, and he hadn't heard a damned thing.
As he adjusted the broadband controls, sweeping the areas where the two subs were lurking, he could hear a difference — faint, but there. Holes in the water…
And he'd missed them both.
Captain Stewart studied the plot board, a remarkably low-tech device for such a high-tech vessel where every few moments a rating marked the position of the Ohio with a wipe-erase pen. The exact positions of the Iranian submarines were not known, of course, but their bearings were indicated by straight lines. As Ohio completed her baffle-clearing turn, however, additional bearings allowed more precise positions to be pinpointed through triangulation.
Ohio had just swung north in order to enter the Straits of Hormuz, running at a depth of just one hundred feet as the bottom shoaled rapidly beneath her keel. Two — at least — Iranian subs were following her, both now astern, but maintaining their positions relative to the Ohio, probably between three and eight thousand yards to the south and the southeast.
"Looks like the trap's been sprung, Skipper," the XO said.
"Well, at least they haven't fired at us," Stewart replied. "Damn, Sierra Two-eight-two could've taken us any time he wanted."
"What are they waiting for? Are they just playing with us?"
"Might be an exercise," Stewart conceded. "But I doubt it. My guess is their orders are to stick close… maybe trail us into Iranian waters."
"Yeah. They could hit us there, and claim self-defense."
"At the very least, they'd screw our mission."
"How'd they find us, though?"
Stewart shrugged. "Wasn't hard, I suspect. With this new configuration, we're not as quiet as we once were."
It was true. Ohio-class boomers were extremely quiet — the better to hide from Soviet hunter-killers during the Cold War. However, Ohio now carried the ASDS on her afterdeck, which went a long way toward ruining her sleek streamlining. Besides, Ohio had been moving at better than twelve knots as she moved up through the Arabian Sea. With some luck, even the relatively poorly trained technicians on board the Iranian boats would have been able to pick her up easily enough.
And this trap had been carefully planned — deploying a number of subs, keeping them submerged and quiet by using oil tankers as cover…
What were they planning?
"So what do we do about them, Skipper?"
"Nothing, for now. There's not much we can do. However, we're going to have to scrape them off when it comes time to deploy. Put your talent in strategy and tactics to that problem, Mr. Shea."