How the Soviet Union Snooped Waters for Enemy Subs—Without Sonar

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Lorenzo von Matterhorn
Jan 31, 2009
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How the Soviet Union Snooped Waters for Enemy Subs—Without Sonar
Newly declassified documents show that even the most secretive submarines leave a trail
23 October, 2017


In the late 1980s, the Soviet Union claimed a feat many military experts thought impossible. K-147, a Victor-class nuclear-powered attack submarine, secretly followed the trail of a U.S. boomer (most likely the USS Simon Bolivar) in an underwater game of chase that continued for six days.

U.S. observers at the time thought the Soviets lacked the tech for effective sonar, at least in comparison to the capabilities of the U.S. and its NATO allies. Now, a newly declassified CIA report shows how hunter submarines like the K-147 went on secret missions to track American subs without using sonar at all.

The CIA's Directorate of Science & Technology produced the report on Soviet Antisubmarine Warfare Capability in 1972, but it was declassified only this summer:

Even forty-five years on, lines, paragraphs, and even whole pages are redacted. A lengthy portion about Soviet technology under development gives details never previously revealed about devices with no Western equivalents. While NATO were concentrating almost all their efforts on sonar, the Russians created something else entirely.

The U.S. and its allies developed sophisticated sonar systems, which soon became so effective that other methods of detection were left behind or forgotten. For decades, non-acoustic methods were considered inferior for being limited in range and reliability compared to sonar. "It is unlikely any of these methods will enable detection of submarines at long ranges," concludes a 1974 intelligence report.

In the USSR, it was a different story. The Soviets were hampered by primitive electronics and struggled to make sonar work at all. So instead they developed other weirdly clever means of submarine detection.

On such method highlighted in the report is the Soviet's mysterious SOKS, which stands for "System Obnarujenia Kilvaternovo Sleda" or "wake object detection system." This device, fitted to Russian attack submarines, tracks the wake a submarine leaves behind. SOKS is actually visible in photos of Russian subs as a series of spikes and cups mounted on external fins.

According to these newly declassified documents, the old rumors were accurate in one way – the Soviets did not develop just one device, but several. One instrument picked up "activation radionuclides," a faint trail left by the radiation from the sub's onboard nuclear power plant. Another tool was a "gamma ray spectrometer" that detects trace amounts of radioactive elements in seawater.

The report also describes how submarines leave behind a cocktail of chemicals in their wake. Sacrificial anodes that prevent corrosion leave a trail of zinc in the water. Minute particles of nickel flake off the pipes circulating seawater to cool the reactor. The system that makes oxygen for the crew leaves behind hydrogen that's still detectable when dissolved in seawater. Together these chemical traces may measure only a few tenths of a part per billion, but sophisticated equipment can find them.

And as you'd expect, a nuclear reactor also leaves behind tons of heat. According to the report, a large nuclear submarine requires "several thousand gallons of coolant a minute". This water, used to take heat from the reactor, may be 10 degrees Celsius warmer than the surrounding seawater, creating a change in the water's refractive index—a change that's detectable with an optical interference system.

And the Soviets did exactly that.

Whether Russians can still stealthily follow submarines, or if the U.S. found a way to foil them, is impossible to know. We'll probably have to wait another 45 years for the [heavily redacted] answer.
If this method was effective or still is, it is scary because the "boomers" are considered to be an indispensable part of our deterrent.
As I was reading it, I was thinking exactly that. Without being able to rely on invulnerable boomers to sit out a counterforce 1st strike on our ICBMs, we'd have to launch on warning which could lead to accidental nuclear war:

Launch on Warning: The Development of U.S. Capabilities, 1959-1979
National Security Archive Electronic Briefing Book No. 43
Published – April 2001
Edited by William Burr


The history of the launch-on-warning capability is a complex one and the declassified record is sparse, no doubt because of the issue's great sensitivity. Precisely when launch-on-warning became a specific option in U.S. nuclear planning remains classified. The documents that follow shed light on the purposes that led to the launch-on-warning option as well as the doubts about its propriety that were raised from the beginning. They include the first declassified discussions of the possibility of launch-on-warning as well the first confirmation that a specialized launch-on-warning option entered into the Single Integrated Operational Plan, the U.S. nuclear war plan, in 1979.