And so it begins, Morris said to himself. PHARRIS was at general quarters for the first leg of the trip away from the U.S. coast. The frigate's tactical towed-array sonar was trailed out in her wake. They were twenty miles north of the convoy, a hundred ten miles east of the coast, just crossing the continental shelf line into truly deep water at the Lindenkohl Canyon. A perfect place for a submarine to hide.
"Show me what you have," the ASW officer ordered. Morris kept his peace and just watched his men at work.
The sonarman pointed to the waterfall display. It showed as a series of small digital blocks, numerous shades of green on a black background. Six blocks in a row were different from the random background pattern. Then a seventh. The fact that they were in a vertical row meant that the noise was being generated at a constant bearing from the ship, just west of north. Up to now, all they had was a direction to a possible noise source. They had no way of knowing the distance nor any of deterrmining if it were really a submarine, a fishing boat with an overly loud motor, or simply a disturbance in the water. The signal source did not repeat for a minute, then came back. Then it disappeared again.
Morris and his ASW officer looked at the bathythermograph reading. Every two hours they dropped an instrument that measured water temperature as it fell through the water, reporting back by wire until it was cut loose to fall free to the bottom. The trace showed an uneven line. The water temperature decreased with depth, but not in a uniform way.
"Could be anything," the ASW officer said quietly.
"Sure could," the captain agreed. He went back to the sonar scope. It was still there. The trace had remained fairly constant for nine minutes now.
But what was the range to it? Water was a fine medium for carrying sound energy, far more efficient at it than air, but it had its own rules. One hundred feet below the PHARRIS was "the layer," a fairly abrupt change in water temperature. Like an angled pane of glass, it allowed some sound to pass through, but reflected most of it. Some of the energy would be ducted between layers, retaining its intensity for an enormous distance. The signal source they were listening to could be as close as five miles or as distant as fifty. As they watched, the scope trace started leaning a bit to the left, which meant that they were pulling east of it... or it was pulling west of them, as a submarine might slide aft of her target as part of her own hunting maneuver. Morris went forward to the plotting table.
"If it's a target, it's pretty far off, I think," the quartermaster said quietly. It was surprising how quiet people were during antisubmarine warfare exercises, Morris thought, as though a submarine might hear their voices.
"Sir," the ASW officer said after a moment. "With no perceptible change in bearing, the contact has to be a good fifteen miles off. That means it has to be a fairly noisy source, probably too far to be an immediate threat. If it's a nuclear sub, we can get a cross-bearing after a short sprint."
Morris looked to the CIC's after bulkhead. His frigate was steaming at four knots. He lifted a "growler" phone.
"Bridge, Combat."
"Bridge aye. XO speaking."
"Joe, let's bend on twenty knots for five minutes. See if we can get a cross-bearing on the target we're working."
"Aye, skipper."
A minute later, Morris could feel the change in his ship's motion as her steam plant drove the frigate hard through the six-foot seas. He waited thoughtfully, wishing his ship had one of the more sensitive 2X arrays being fitted to the Perry-class fast-frigates. It was a predictably long five minutes, but ASW was a game that demanded patience.
Power was reduced, and as the ship slowed, the pattern on the sonar screen changed from random flow noise to random ambient noise, something more easily perceived than described. The captain, his ASW officer, and the sonar operator watched the screen intently for ten minutes. The anomalous sound tracing did not reappear. In a peacetime exercise they would have decided that it was a pure anomaly, water-generated noise that had stopped as unpredictably as it had started, perhaps a minor eddy that subsided on the surface. But now everything they detected had a potential red star and a periscope attached.
My first dilemma, Morris thought. If he investigated by sending his own helicopter or one of the Orion patrol aircraft, he might be sending them after nothing at all, and away from a path that could end with a real contact. If he did nothing, he might not be prosecuting a real contact. Morris sometimes wondered if captains should be issued coins with YES and NO stamped on either side, perhaps called a "digital decision generator" in keeping with the Navy's love for electronic-sounding titles.
"Any reason to think it's real?" he asked the ASW officer.
"No, sir." The officer wondered by this time if he had been right to call it to his captain's attention. "Not now."
