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SOSUS: Spying on Soviet Submarines

As far as outrageous Cold War spying escapades go, this is a good one. The Sound Surveillance System (SOSUS) was an American initiative that deployed an underwater listening system intended to track Soviet submarines. Initially set up in the Atlantic, it eventually spread and was later installed in the Pacific.

By placing hydrophones (underwater microphones) on the ocean floor, the Americans and most likely the British also were able to track Soviet activity across the Atlantic Ocean. This was a practice that went on for decades and only fully came to light in 1991 after the fall over the USSR – although by that point it had been an open secret for some time. 

This also led to some tantalizing stories of how Soviet submarines who had assumed they had evaded detection were being tracked closely by American submarines without them knowing. If that doesn’t sound like a great setup for a movie, I don’t know what is. 

As you might imagine, even after declassification there is still plenty of mystery surrounding this project that as far as we know is still ongoing.  

Early Sonar  

The detection of submarines has always traditionally been through the use of sonar, which works by sending pulses of sound waves through the water and then measuring how long they take to hit an object and then bounce back to the transmitter, where they are rather nicely displayed on a screen that we can read. 

LEONARDO DA VINCI by Alison restrepo quiroga is licensed under CC-BY-SA

Several animals use a form of sonar – dolphins, bats and apparently some shrews – which is news to me. For the first human use we need to go back over 500 years ago to the Jack of all trades, Leonardo De Vinci, who found that by placing a tube in water then putting your ear to said tube, you could detect vessels in the water close by. 

The first time we see stationary hydrophones placed in water came during World War I with the work of J. Warren Horton whose rudimentary hydrophones were first tested off the coast of Nahant in Massachusetts and who was in the process of laying more in the Irish Sea when peace was declared. 

Not a great deal happened on the sonar front from the end of World War I to the outbreak of World War II. But once the world found itself in the grip of a global war once again, nations around the world kicked their sonar capabilities into overdrive. 

The Sofar Channels

Amid bedlam that was World War II, some quite extraordinary scientific discoveries were made. Some, like the atomic bomb, made killing even easier, while others like radar, synthetic rubber, and even the full potential of penicillin, have had wide-ranging benefits since the conclusion of the conflict. 

Another discovery, perhaps not quite as dramatic, but important nonetheless was the discovery of Sound Fixing and Ranging channels (SOFAR). These are naturally occurring channels underwater, approximately 1,000 metres (3,300 feet) down, where the speed of sound is at its minimum, meaning that sound can travel vast distances before dissipating. To give you a very basic example, remember as children you would make those string paper cup phones? Well, this is a little bit similar. Although it’s underwater and the distances can be hundreds of miles apart. 

This was discovered separately by Maurice Ewing and J. Lamar Worzel at Columbia University and Leonid Brekhovskikh at the Lebedev Physics Institute Moscow in the 1940s, but large scale testing didn’t happen until 1944 when Ewing and Worzel hung a hydrophone from a ship while a second vessel 1,700 km (1,000 miles) miles away set off an explosive charge. The effect was even better than had been anticipated.      

The Cold War Begins

The carnage that the German U boats had inflicted during World War II showed the world just how devastatingly effective these monsters creeping through the depths could be. As the U.S and USSR began their marathon arms race the numbers of submarines on both sides exploded. By the end of the 1950s, the United States was preparing to introduce its first submarine armed with submarine-launched ballistic missiles. The USS George Washington with its 16 Polaris A-1 missiles entered service in 1959 and it’s probably fair to assume that the Americans knew the Soviets were not far behind. 

And when I say not far behind, I really mean at almost exactly the same time. The Soviet K-19 submarine was completed in 1960 and suffered a complete loss of coolant to its reactor on its maiden voyage. Only the heroic efforts of the crew who were able to construct a temporary coolant system managed to avert a complete nuclear meltdown. However, the contamination onboard the K-19 had been extensive and within two weeks 8 crew members had died. Within two years, that number had reached 22. In true Soviet style, the cause of death was not recorded as radiation poisoning, but rather down to astheno-vegetative syndrome – a mental disorder. But the crew of the K-19 were under no illusions of what had happened and gave their cursed submarine a new nickname – Hiroshima.

The oceans were becoming an even more dangerous place and with the introduction of ballistic missiles that could be fired from anywhere on the planet, both sides were eager to gain any advantage they could. 

SOSUS Research

The origins of SOSUS began in 1949 with a set of recommendations from a study group known as Project Hartwell, which had been tasked with researching anti-submarine warfare. It concluded that the U.S should spend $10,000,000 (equivalent to $107,450,000 in 2019) annually to build and maintain a vast array of hydrophones that could take advantage of the sound superhighways of the SOFAR channels. 

A series of projects then got underway, some of which remain mysterious even to this day. Project Jezebel explored the use Low Frequency Analysis and Recording, using a Low Frequency Analyzer and Recorder, which confusingly both use the same acronym (LOFAR), to give a visual representation in real time of frequencies picked up from buoys in the Atlantic Ocean. This was done using AT&T’s sound spectrograph which had originally been developed for speech analysis but was now modified to analyze low-frequency underwater sounds. Basically, these can provide a permanent visual record of sound energy from a particular point. Nowadays, you can hold a LOFAR in your hand, but back in the 1950s, these Lofargram writers were enormous contraptions.    

This was greatly expanded on by the, slightly wordy, AN/SSQ-28 passive omnidirectional Jezebel-LOFAR sonobuoy, which began to be used in 1956 as a way of transmitting data taken from buoys directly to aircraft above. By using Bell Telephone Laboratories time delay correlation, users were able to fix the position of a submarine or vessel using two or more buoys, a technique known as COrrelation Detection And Ranging (CODAR).


Between 2nd and 19th January 1952, the British cable layer Alert worked to install the first experimental, yet fully operational SOSUS elements off the island of Eleuthera in the Bahamas. This included a 304 metre (1,000ft) long array (the wiring system that connects it all) complete with 40 hydrophones laid on the ocean floor, 438 metres (1,440ft) down. 

Initial tests with a target submarine proved successful and a further nine arrays were ordered and laid in the Western North Atlantic. In 1954, ten more arrays were added, but this time spreading out, with three in the Atlantic, six off the western coast of the U.S and close to Hawaii.  

These arrays and their hydrophones needed to be connected to facilities onshore where a LOFAR machine was located. This was done with a multi-pair wire but with a maximum length of 241 kilometres (150 miles) it meant the entire system needed to remain relatively close to land. The arrays were often positioned on continental slopes or seamounts at a section where deep sound channels typically converged. 


What was first placed in the late 1950s worked, but was quickly improved upon over the coming decades in what came to be known as the Caesar Phases and included the installation of multiplexed coaxial cable and major upgrades in the shore facilities which included the Digital Spectrum Analysis (DSA) which measures the power of the spectrum coming from a signal, speeding up the accuracy of detection. Further cable upgrades were placed in 1972 and in 1994 SOSUS prepared for the 21st Century when its original cables were replaced by fibre optics.  


The extent of which U.S authorities were able to successfully track Soviet submarines isn’t always entirely clear. Without knowing the exact number of vessels officially operating in an area, it’s difficult to get an exact read on just how successful SOSUS was – but we do know the first time it successfully picked up a Soviet submarine. 

On 6th July 1962, NAVFAC Barbados was able to track a Soviet Submarine close to Norway as it moved through the Greenland-Iceland-United Kingdom (GIUK) gap – it became known as contact #27103. There are some stories of a U.S submarine then quietly following behind undetected, but unfortunately, this can’t be verified. 

In 1968, SOSUS tracked its first Victor and Charlie class Soviet submarines and in 1974 a Delta Class Submarine was also tracked for the first time. Perhaps one of the most extraordinary uses of SOSUS came in the build-up to Project Azorian. Now, we’ve done an entire video on this subject on megaprojects so I won’t say too much on this topic and if you want to find out more then shoot over to that particular video after this. 

Project Azorian was the barely believable tale of how the U.S successfully located and then tried to raise a sunken Soviet Submarine – the K-109. This was a nuclear-powered submarine that disappeared in 1968 and despite extensive searching, Soviet authorities weren’t able to locate it. 

But the Americans did – and guess how they did it? By using their SOSUS system they were able to pinpoint the location of the underwater explosion that had ultimately doomed the submarine. As I said, what came next is barely believable, but the Americans essentially built a ship that could pick up a submarine and hide it inside. But let’s not get sidetracked. For more on Project Azorian take a look at our full video. 

SOSUS was also used to locate two U.S submarines that had sunk, the USS Thresher in 1963 and the USS Scorpion in 1968. You’d be amazed how many nuclear submarines have sunk over the years – eleven at the last count. 

Problems with the System

While this system worked in that it could detect submarines and large objects in the water, it came with numerous problems. When SOSUS began operation, those working on it had no idea what a Soviet submarine sounded like. This was still a long way from the signature library of Soviet submarine acoustics that was later compiled. Those scanning with the LOFAR were doing so pretty much blind and there were plenty of vessels in the water at that stage. Only after the Cuban Missile Crisis of 1962 when the U.S set up a blockade around the Caribbean island did the traffic in the area reduce and those listening through SOSUS began to hear unusual underwater signatures which were soon deemed to be Soviet submarines. 

Then there was the question of secrecy and the rather bizarre distrust between the surveillance community and the Navy. The information gathered by SOSUS was rarely shared widely with the naval fleet in the vicinity, while the U.S Navy for some reason believed that their submarines couldn’t be heard by SOSUS. When the system successfully picked up the USS George Washington in 1961 the Navy began a process of quietening their submarines in response. 

Lastly, and perhaps most dangerously, the lack of communication between those involved sometimes led to mistaken identity. Something which happened in 1962 and 1973 when U.S submarines deployed on classified missions close to the Soviet coast were picked up by SOSUS, which then relaid the incidents up the chain of command as they couldn’t be sure what they had heard. Though nothing ever came of these incidents, it did expose the frailties of the SOSUS system when combined with a lack of communication.   

Post Cold War

SOSUS was officially declassified in 1991, but by this point, it had been an open secret for some time. The immediate need for SOSUS disappeared almost overnight and the number of people involved in it came tumbling down, from a reported 4,000 during the 1980s, to just 1,000 by 2010. The number of shore installations has also been drastically reduced, but a presence remains on the east and west coast of the United States, as well as one further station out in the Pacific Ocean. 

Compared with other technological developments that occurred after World War II, SOSUS might not sound particularly impressive, but the fusing of natural elements in our world with modern technology was groundbreaking. It’s a service that certainly has its limitations and how effective it is at picking up modern submarines which are considerably quieter is another matter, but until we develop satellites that can scan underwater, it’s likely SOSUS, in some form at least, will continue to keep its ear to the ground – or rather to the water.

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