Hide Silent, Hide Deep: Submarine Tracking Technologies Of The Cold War

All through the cold war, there was a high-stakes game of cat and mouse in play. Nuclear powers like the United States and the Soviet Union would hide submarines armed with nuclear missiles underwater. The other side would try to know where they were so they could be targeted in the event of war. The common wisdom was that the United States had many high tech gadgets to help track enemy submarines, but that the Soviet Union was way behind in this area. This was proven false when a Soviet Victor-class boat followed a US missile submarine for six days. Now, a recently declassified CIA report shows how the Soviets didn’t use sonar at all but developed their own technology.

There is something fascinating about submarines. Like an old sailing ship, submarines are often out of touch with their command bases and the captain is the final authority. Like a space ship, the submarine has to survive in an inimical environment. I guess in all three cases, the crew doesn’t just use technology, they depend on it.

Although the submarine has some non-military uses, there are probably more military subs than any other type. After all, a sub is as close to a cloaking device as any real-life military vehicle has ever had. Before modern technology offered ways to find submarines using sonar or magnetic anomalies, a completely submerged submarine was effectively invisible.

There was a lot of speculation that the Soviet Union lacked sufficient technology to use sonar  the way the US did. However, in some cases, they had simply developed different types of detection — many of which the West had discarded as impractical.

Modern Submersibles

Oddly enough, people have been trying to figure out how to operate underwater since the time of Alexander the Great. The first submarine that has features similar to a modern sub was the Catalan Ictineo II. It ran on a steam engine when on the surface, but submerged used chemicals to fire the boiler. The chemical reaction not only created heat for the steam engine that turned the screw but also released oxygen for the crew. A few German submarines used a similar system known as the Walter turbine.

Things progressed from there (you’ll find plenty of historical detail in the video above). The biggest problem was always how to power the craft when submerged. Prior to atomic energy, most subs ran on diesel on the surface and had batteries to power it underwater. A snorkel would allow the engine to run while staying mostly submerged, but once the ship sank completely beneath the waves, it had to use batteries which don’t last very long — especially 1940-era batteries.

Strategy and Nuclear

The technical side of the submarine directly influenced the tactical side. Although a submarine on the surface isn’t in a particularly safe place, World War II-era subs spent a lot of time on the surface, allowing them to make better speed. If a sub crew thought it might encounter the enemy, the vessel would submerge, at least to snorkel depth, to try to avoid detection.

Approaching an enemy convoy submerged, it would try to sink as many ships as possible using torpedos or whatever weapons it had. It had to work fast, though, because firing usually gives away your position and the inevitable counterattack would be swift. The Navy gave a lot of thought about how to locate and attack submarines, as you can see in the video below.

In modern times, though, submarines may use a different form of power: nuclear power. In that case, the sub can stay submerged for a very long time. This has led to military subs having two main categories: attack subs and missile subs, sometimes known as boomers.

The idea behind a missile sub is to have it leave port with a stockpile of nuclear missiles. Usually, the sub will do some crazy maneuvers to try to shake any enemy ships following it. Then it will go deep and wait. The idea is that if an enemy tries to attack first, it could wipe out ground-based missile launchers. But they can’t strike a submarine unless they know where it is, so the submarine fleet could retaliate no matter how successful a first strike was. Under the doctrine of mutually assured destruction, this would prevent either side from thinking a first strike is their best option.

In Practice

The United States relied on advanced sonar, radar, and infrared detection to find subs. It also could use very sensitive magnetic detectors to locate submerged metal objects. Some of the sensors are on ships, subs, or airplanes.

All of these have some limitations. However, the SOSUS (sound surveillance) line deployed ultrasensitive hydrophones on the ocean floor at key locations to identify and locate submarines. These microphones were connected to the shore using the same sort of cables used for long-distance circuits. Using state-of-the-art signal processing and microphones, the US could reasonably track the relatively noisy subs. You can learn more about SOSUS in the video below.

However, nuclear boomers posed some unique challenges. They can sit quietly on the bottom for a very long time. They can attack without approaching the enemy. A single submarine can launch well over 100 warheads, each with enormous destructive power.

The CIA pointed all of this out way back in 1973. Even though the Soviets had some unique technology, the CIA deemed that the “…capabilities for antisubmarine warfare fall far short of the minimum requirements…” That is to say the US boomers had nothing to fear from the Soviets. The video below shows some of the ways the US located submarines.


On page 14 of the CIA report, there is an assessment of Soviet detection capabilities. There are several pages in that area completely redacted, so you can only wonder what is there that is still secret.

The report details Soviet sonar and magnetic detection capability, but they were not overly impressed with the equipment or how the Soviets used them. They do mention briefly that circumstantial evidence indicated that some aircraft could have an infrared wake detector. But thanks to the redactions it isn’t clear what the evidence is.

Since the Soviets lacked a widespread underwater detection system like SOSUS, their best bet — according to the CIA — was to find a submarine and follow it. This is known as “trailing.”

Annex A

The real interesting bits of the report begin on Page 63 where Annex A starts. This annex analyzes methods the Soviets use to detect subs. The fact that the Soviets didn’t have something similar to SOSUS the CIA attributes to their lack of access to deep ocean and a deficiency in cable technology. In addition, the report cites a lack of signal processing ability and the predominant use of rigid hydrophones. Besides that, US subs were significantly quieter than Soviet subs of the time. Even SOSUS could not reliably detect US subs, so for the USSR to build a useful capability like SOSUS, they would have to do a better job of it than the United States had.

Perhaps the Soviets knew that, too. Instead of trying to spend more money to develop better active and passive SONAR, they turned to other ways to track subs. For example, there was interest in detecting 5 Hz noise generated by a sub’s wake. They also relied on magnetic detection using similar technology to the United States. There was also work to use radar to detect things as subtle as a submarine’s disturbance of the water on the surface above it.

Of course, the subs most valuable to track have reactors. They produce a lot of neutrons, but the water absorbs most of them so it is hard to detect them from any distance away. Antineutrinos, on the other hand, are very hard to absorb. So hard, that it is difficult to detect them, too. The CIA didn’t rule out the Soviets using such a system even though there was no evidence that they had.

However, some other radiation effects are easier to track. The Soviets claimed success tracking their own nuclear subs by measuring radioisotopes in seawater, but there is no evidence they used this technique operationally. They also could detect a submarine’s wake optically or acoustically — possibly useful if a Soviet sub was trailing another sub. There are also methods using chemical residue from a sub’s hull or using infrared.

Wake detection is how the K-147 probably followed the US sub. A system known as SOKS (System Obnarujenia Kilvaternovo Sleda) had been on some Soviet boats since 1969. The cluster of probes measured several things including nuclear byproducts and other parameters mentioned in the CIA report.

Mutually Assured Missiles

The boomer subs were a key part of cold war strategy. The US had the Ohio class submarine and its Trident missile with eight 100 kiloton warheads. The Soviets had the huge Akula with its larger R-39 missiles. The Akula — known as the Typhoon class in the West — was the largest sub ever and could hold up to ten 100-200 kiloton devices (see the video below).

The sub was known to be pretty noisy, though, so SOSUS supposedly knew where they were all the time.

Cold War

We don’t miss the cold war. But it did produce some amazing hardware and technology. Besides, there’s something thrilling about reading a document that would have been full of highly classified information in its time. Even though none of it is secret almost 50 years later, if you ever needed to detect submarines, this document would give you a lot of ideas on areas to research.

48 thoughts on “Hide Silent, Hide Deep: Submarine Tracking Technologies Of The Cold War

  1. Recently I had a chance to repair a military sonar used on ORP Bielik. Its PA section is based on GP-5 high voltage vaccum tube. From what I remember from service manual this lube was chosen specifically because it allows large cock speed without stressing other components.

    1. Being a cold war fast attack submariner it seems this time the US behind in capabilities. The US will have to train the submarine fleet to track again with no one left from the cold war to look to.

  2. https://www.scmp.com/news/china/science/article/2166413/will-chinas-new-laser-satellite-become-death-star-submarines
    >In theory, it works like this – when a laser beam hits a submarine, some pulses bounce back. They are then picked up by sensors and analysed by computer to determine the target’s location, speed and three-dimensional shape.

    >Experiments carried out by the United States and former Soviet Union achieved maximum detection depths of less than 100 metres, according to openly available information.

    >That range has been extended in recent years by the US in research funded by Nasa and the Defence Advanced Research Projects Agency (DARPA). A device developed by DARPA, for example, was mounted on a spy plane and achieved reliable results at a depth of 200 metres, detecting targets as small as sea mines.

    China wants to build a satellite that goes for 500 meters.

    1. “China wants to build a satellite that goes for 500 meters.”

      And subs will be coated with anti-reflection coatings, as well as shapes that don’t reflect UP. They may even start inking like a squid.

      1. Or maybe US NAVY ONR will take more lessons from cephlapods than just inking. How about active camouflage chromatophores paint from nanotechnology?Just watch a cutttlefish and be amazed. Sometimes you can’t even see a squid or octopus right in front of your face, Imagine using active chromatophores to refract b/g laser light AWAY from the sub? They also are shape-shifters too with special muscles. The active camo sub could use metamaterial nano-mirrors to refract LASERS (and possibly to optically disappear too)..

        Click my website (sotb) to see cuttlefish in action…

    2. An ocean is a BIG place. Like, really hugely bigly big. Even if the laser beam were ridiculously wide (say, hundreds of yards square), I don’t see how this technology could be used to find a sub without at least some prior knowledge of where to search. Anyone got more on this topic?

  3. Cavitation can occur at the tips of propeller blades which has the undesirable effect of providing a trackable acoustic signature. The U.S. developed cavitation reducing blades for its submarines. Toshiba sold the U.S. design to the Soviet Union.

    1. I thought they sold the same (highly complex) milling machine to the Soviets, allowing them to make their props quieter.

      As has been mentioned before in HaD. The prop is very secret, submarines being shown to the public have a shroud covering the prop(s) to hide their geometries.

    2. Years ago I read of an incident where a company sold some advanced CNC milling machines to the USSR. They were on the restricted list of things not to sell to them, or China. But the people who wrote up the restrictions left some holes. Sold without the control computers from the USA the machines were “parts”. The Soviets then obtained controllers capable of being modified to run the CNC machines from one of the neutral countries like Sweden, also via some twisted paths in order to circumvent export restrictions. Within a year of that happening the Soviet subs were quieter due to them being able to machine more complex and precise propeller shapes.

    1. The NATO name for the Akula class SSBM is Typhoon.
      The NATO name for the Shchuka-B SSN is Akula.
      The USSR did not tell NATO the name of it weapons so NATO made up reporting names. In this case you had a collision in naming. Probably because NATO ran out of phonetic alphabet names and decided to use the Russian word for shark for a new class of attack sub while the USSR used the Russian word for shark for their largest SSBM.

    1. When we can find a system of neutrino detection which is not the size of a swimming pool, then maybe fine. Neutrino’s are incredible elusive and difficult to detect. Detecting them from something like a submarine reactor would be very difficult.

  4. Straight out of the HaD style manual: writer starts by talking about how a bunch of stuff is redacted and concludes with “How wonderful to read stuff that’s no longer secret!”

  5. I was on an SSBN in the 70s. The Russian ships — called AGI’s– used to follow us until we dove. They got so close you could look them in the eyes. Interesting article.

  6. There are some really simple methods to detect large metal objects at high depts such as variations in the fieldstrength of LF and VLF transmitters.
    Also nice to find deep cables and pipes. The only difficulty is that you have to scan the area using a plane. but I can assure you that is has been successfully done.

  7. A submarine based nuclear deterrent in the age of AI systems does not need to be much larger than the delivery system for the actual weapon. They could be deployed secretly from underneath a ship and potentially loiter at great depths for as long as ten years, just waiting for a signal, or the cessation of a signal, before they rise to the surface and launch the missile. The only reason that there were such large vessels in the past was due to the need to accommodate so many crew and their equipment for such a long time. The Chinese and Russians are busy modernising, but their vision of “modern” is still 50 years out of date. The systems of the mid 21st century would seem like science fiction to people today, but they will not hear about them for another 50 years, and by then AI and robotics, automated everything, will be commonplace. Recall the saying (Gibson?) that the future is here but unevenly distributed, well the US military, and their friends, gets to experience the future first.

  8. I worked on Sonars in the 80’s. I am pretty sure Russian Sonar capability was OK, if bulky, missing the miniaturization technology in the West and the performance required for signal processing. Magnetic anomaly technology was used, but gave too many false positives so what not relied on.

    The other thing to say is that boomers then were pretty noisy, far quieter were hunter killers

    I spent a fun 6 weeks outside Murmansk watching the pride of the Russian submarine fleets come and go. Mainly Deltas, but the Akula’s were impressive, while the Typhoon was massive

  9. How long has it taken to find “downed” air liners in large CHUNKS wit the whole world looking for any parts? THEN not finding any parts intentionally but by “accidentally” having hunks of planes wash up on some island where it NEVER could ha gotten to ? Just asking….

  10. It occurs to me, reading the report, that much of what they believed the Soviets to have been working on may have been due to their knowledge of the U.S. developing these technologies. That is, if WE’VE thought of something, and it looks promising, then probably the Soviets are also investigating it.

    In 1976 I was a USAF RADAR technician. Note that this was just a few years after the report that is the subject of this article was written. At the time, research was being done to develop specifications for the next generation of fixed-site aircraft surveillance RADAR systems, and a mixed civilian/military team spent about a week making detailed measurements of our systems, including antenna patterns and the characteristics of both our transmitted and received signals, including a number of measurements of the exact times when “sun strobes” were observed, indicating when our antenna was pointed directly at the sun. At one point, they told us that our antenna was pointed too high, and had us tilt it down half a degree. The implication was that it was higher than its specified elevation, and I wondered how it could have fallen out of spec, since the platform was perfectly level, and the elevation angle was fixed, and making the half-degree adjustment required moving the feedhorn, which clearly had not been moved since its installation, a considerable distance. So if it was out of spec, then it must have been installed out of spec. Which of course is possible. But now I realize that it may have just been higher than they (then) wanted it to be.

    One of the engineers on the team was working with a gated digital spectrum analyzer, that could show the spectra of received signals at extreme frequency resolution, at specific ranges from our site. The antenna was at the time stopped, and pointed out into the Bering Sea. (On a good day, with sufficient atmospheric inversion, we could see Russia from our antenna deck…) He dialed his range gate to 150 nautical miles, +/- about 1 mile, fiddled with the gates for a little while, and showed me a waveform with six peaks in a distinctive configuration that he called an “angel”, implying that it was a common enough signal to have a name. He made some measurements on it and told me it was an ocean wave traveling at x knots relative to us, 150 nautical miles away.

    At the time, I thought it was an impressive display of what could be gleaned from signals, with sufficient signal processing. It’s only after reading this report 44 years later, that I realize they may have had a specific reason for looking at the ocean surface itself at a distance, using a system designed for detecting aircraft. Fascinating.

    Years later, I saw the report from that survey, which had involved several different RADAR sites, including the one I was at. Much of the (unclassified) report confirmed what I remembered about the survey, but no mention was made of lowering our antenna, nor of any measurements of waves at a distance. There was some discussion about “sea clutter”, but only in the context of this being a source of false targets. Still, if “sea clutter” was a concern, then why would they have us LOWER our antenna angle?

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