I stared at him. "No big thing? Jesus Christ! We're in the middle of the ocean, Brian," I said. "There's not supposed to be anybody else out there."
"It could be from a thousand things," he said, dismissing the more ominous implications.
"Or it could be somebody has found us."
"Survey ships, war games by our guys, fishing fleets detonating fish to the surface, it could be anything."
Glancing back at the reactor control panel, I scanned the meters and looked for anything even slightly abnormal as more explosions went off. I adjusted the reactor control system and shifted around in my chair.
The man of the house is looking for the intruder, I thought.
Behind us, Lieutenant Katz called the control center, asked couple of questions, and listened carefully. "The captain doesn't know what the sound is," he said, hanging up the telephone "The sonarmen think the noise is probably coming from a sonobuoy dropped by something-an aircraft, a ship, or maybe even another submarine."
Another explosion went off, and all of us waited for the next one.
"Goddamn!" I said as I put my clipboard down and waited.
"Somebody out there is exploring the thermoclines," Katz said, referring to the layers of water created by virtue of their different temperatures. A layer of cool water next to warmer water causes the deflection of sonar waves; objects, such as submarines hiding on the other side of the thermocline, are concealed from detection by ships on the surface. To improve the chances of finding deeply submerged vessels, floating sonobuoys eject explosive charges that drop deep below the surface. When the charge sinks to a pre-determined level, it detonates and the sonobuoy broadcasts any reflected echoes to a receiving ship or aircraft.
It is a tricky business because of the "tunnel effect" that echoes the explosive sound back and forth down the tunnel for many miles and confuses everybody about distances. If we were sitting at the end of a long thermocline tunnel, an explosion from five or ten miles away could sound like it was right outside our hull. Unfortunately, there is no easy way to determine whether or not a tunnel is present. We had no way of knowing if the explosions were from a distant source or right outside our boat.
10. Man overboard!
In early 1968, a Soviet Echo II submarine designated PL-751 ("PL" for podvodnaya lodka, or submersible boat), with ninety men on board, returned to her home port of Vladivostok on the eastern coast of the Soviet Union. For a prolonged duration, she had been on station within range of U.S. targets, and her captain and crew were looking forward to several weeks of well-earned time ashore. According to the timetable of Soviet submarine deployment, she was to be relieved by her sister ship, currently undergoing preparation and scheduled for departure at the Vladivostok submarine base.
To the distress of the men on board PL-751, they were informed on arrival that their relief ship had developed mechanical problems and would not be able to deploy. PL-751 was forced to stock up on food and supplies, cast off her lines, and immediately return to sea for another prolonged period on station in the Pacific Ocean. As she cleared the Sea of Japan, her cavitating screws broadcast their characteristic signature to the listening SOSUS array below. The sounds, as well as her northeast direction of movement, were duly noted by the U.S. Defense Intelligence Agency (DIA) monitoring specialists who were thousands of miles away. Cruising north of the Japanese island of Hokkaido, PL-751 passed over the deep Kuril Basin at the edge of the Sea of Okhotsk, navigated between the Kuril Islands, and finally powered into the open waters of the Pacific. She maintained full 30,000 SHP (shaft horsepower) from her twin shafts and dual reactors. Crossing the undersea Shatskiy Rise and approaching the Emperor Seamount, she moved in the direction of her patrol sector within missile range of Midway and the Hawaiian Islands.
When PL-751 reached an area in the northern mid-Pacific Ocean, a region pinpointed at exactly 35° N, 172° E, a violent event destroyed the submarine's watertight integrity. The precise nature of this event is unknown, but it was possibly the result of an explosion from hydrogen gas during battery charging operations, an explosion during the handling of missile fuel, or human error as the fatigued crew pushed themselves and their submarine beyond the limit.
The captain and crew immediately struggled to save their ship as she took on increasingly high-pressure water and slid deeper into the ocean toward her test depth. Within several seconds of the time when she roared past her maximum designed safe depth, the waters of the northwestern Pacific Ocean were filled with the popcorn noises of rupturing pipes and bulkheads as the PL-751 accelerated through her crush depth and delivered her entire crew to the bottom of the ocean, 19,200 feet beneath the surface.
The Soviet Union made no announcement to the world about the sinking of the PL-751, and the United States released no information about the sounds that had found their way into the SOSUS microphones at the bottom of the Pacific. During the next several days, American intelligence forces monitoring Soviet ship and aircraft movements recorded an unprecedented number of radio message intercepts originating from Petropavlovsk-Kamchatskiy on the Kamchatka Peninsula and Vladivostok. Also, during this time, satellite and other highly classified sensing systems recorded a dramatically increased number of Soviet naval and air search operations traversing the routes of U.S. task forces patrolling in the North Pacific.
The explosions, carrying up and down the thermoclines, continued to vibrate the hull of the Viperfish, but we tried to ignore the noises and the implications of their presence. Occurring at irregular intervals for several weeks, they disrupted our sleep, frazzled our nerves, and made everybody feel miserable. During this time, we relentlessly pursued our search of the ocean bottom. As the weeks stretched into a full month with no sign of success, morale plummeted even more. The most ominous sign of widespread discontent was the oppressive silence that began to emerge throughout the Viperfish as the Fish found nothing, the explosions continued, and our hope for success waned. When the crew was happy, everybody groused about everything; when the crew was depressed, silence prevailed. The Viperfish's crew was becoming silent.
As we roamed our search area, the civilians and Special Project crewmen debated the best way to scan the bottom of the ocean for our target without missing any areas. Some previous experience with towed devices, similar to the Fish, had been documented in the archives of U.S. search projects, such as that by the USS Mizar, the oceanographic research ship that had found a nuclear bomb off Spain, but there was almost no experience with a submarine towing miles of cable.
Is it best to move in a straight line back and forth across the search area, they wondered, with the potential of losing the "lineup" during each complicated turnaround procedure? Should the submarine encircle a central point by starting with a huge circle that gradually becomes smaller and smaller? Maybe the circles should start at a central point and expand by ever- increasing diameters. Or would it be better to make equal-sized circles overlapping in a single direction that would result in a wide swath of searched ocean bottom, hopefully performing in such a manner as to rule out any missed areas.
There were no books on the subject and little information beyond the Mizar data. Most of us were vaguely aware of the Mizar's successful operations, which included finding the USS Thresher in 1964, but the Mizar was fundamentally different from the Viperfish: she was a surface craft. Searching the bottom of the ocean in a vessel heaving around on the surface is, in some ways, more of a challenge than it is in a submarine that remains at a fixed depth below the surface.