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.

Detection

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.