ocean offered, including anomalous acoustic conditions, to evade contact.
Don’t matter if she knows we know, Rabies thought, banking the S-3B
sharply to get into position for the next drop. She already knows about us!
“All buoys sweet and cold,” Harness reported, telling the rest of the
flight crew that each buoy was operating properly and that none of the buoys
had gained contact on the submarine.
“She can’t have gotten far,” the TACCO muttered. “She only dived ten
minutes ago. She’s got to be in the area!”
“Acoustic conditions aren’t the best,” the AW said. Both of his hands
were on his head, pressing the earphones tightly over his ears. He took one
hand off, reached for his water bottle, and took a swig. “Warm, shallow
water. Couple of deep trenches nearby. I’m betting she heads for one of
those.”
Sound energy, the TACCO knew, was essentially lazy. Or at least that’s
how it had been explained to him in his earliest days as a student naval
flight officer. It always seeks out the path that lets it travel the slowest.
The actual mechanics of sonar detection and layers in the ocean were explained
in a mathematical formula known as Snell’s Law. For the TACCO’s purposes, the
“lazy” analogy was sufficient.
Three factors made sound travel faster: heat, pressure, and salinity.
Increase any one of those elements in a layer of water, and sound energy would
bend away from that layer.
The South China Sea had a hard, rocky bottom. This near the equator, the
water on the surface of the ocean was continually warmed by the sun. Wave
action mixed the surface water with the layer below it, creating an isothermal
layer of warmer water approximately fifty feet deep. The depth varied,
depending on time of day and the sea state. At night, the surface of the
ocean cooled down slightly. During heavy weather, rougher seas mixed the warm
water even deeper into the ocean.
If the DICASS buoys were dropped in the shallow surface layer, the
returning pings would be trapped below the warmer area of water and would not
return to the DICASS receiver. The AW, knowing the characteristics of this
part of the world’s waters, had set his buoys at a depth of two hundred feet,
well below the layer.
“Could be anything,” the AW continued. “There’re enough pinnacles and
rocks down there to block the return. Or, if she headed in toward the
coastline, the water might be too shallow to get a good return. I don’t know
if–Wait!” he said suddenly. He pressed the headphones more tightly against
his ears.
“Buoy fifteen hot!” he said. “Bearing 310, range four thousand yards!”
The TACCO glanced at his display. “Westernmost buoy. Makes sense–she’s
running for the shoreline and shallow water. And for Vietnamese territorial
waters. She knows we’re going to be reluctant to follow her in there,
regardless of her nationality. I can damn near guarantee that if we shoot a
torpedo into territorial waters, we’re going to hit something that’s going to
get us in trouble. Murphy’s Law.”
“Lost it,” Harness announced. “She was there, though. I’m sure of it.”
“How the hell did she get that far without us hearing her? She’d have to
have been making better than twelve knots–we had to have heard something, at
that speed. Let’s lay another pattern,” the TACCO said. His fingers flew
over the display, calculating the spacing between buoys, and then punched the
information up to the pilot’s display.
“Sir, you’re right,” the AW said thoughtfully, staring at his display.
“She makes that speed, I’m going to get her, layer or no layer.”
“But the DICASS contact was solid, right?”
“No doubt. Too hard and sharp to be a biologic,” the AW answered,
referring to the possibility that the DICASS buoy could have pinged on a whale
or pod of dolphins. Even clouds of shrimp composed of millions of the tiny
creatures could reflect back the sound energy from a DICASS buoy.
“And I didn’t hear any biologics. No, I had a sniff of a sub, sir. No
doubt.” The AW’s voice was firm.
“Okay, so we chase her down and sink her,” Rabies broke in. “Come on,