Intro-The Soviet fleet was expanding rapidly and so was its submarine arm, which was receiving top of the line SSNs and SSBNs in large numbers. The allies had learned about a submarine’s capabilities the hard way in both world wars during which German U-Boats had almost bought Europe onto its knees by cutting off its supplies from America. Hence they employed a unique solution named SOSUS ie Sound Surveillance System to counter the threat of Soviet submarines.
At the start of the Cold war, the Soviet Navy didnt have a formidable submarine force like the western countries. As the years went by development and construction of nuclear and conventional subs was started. Large numbers of subs which could hit allied cities were commissioned. The allies however had a geographical advantage.Thanks to the unique geography of the region most of the Soviet subs had to pass through the GIUK gap ie gaps between Greenland, Iceland and UK to reach the Atlantic. Hence the allies decided to install sonar sensors in these gaps so that no Russian sub could enter the Atlantic without being detected through this gap. It is speculated that such sensors were placed in the Pacific as well.
The facilities which received the signal caught by these arrays were similar to NASA’s mission control center. A typical facility had several small consoles which monitored signals from one specific area. The areas covered by a single console were overlapped thus several operators were listening to sounds from a particular place. If they find a new contact, they would report it to their chief who would inturn inform USN command which would send assets to keep a tab on it.
In case of a war, allied ASW assets like SSNs, ASW aircraft for eg Nimrods and Orions, ASW vessels like Type 22 frigate of the RN operating in the area would be sent to hunt for any Soviet SSNs and SSBNs before they could reach the Atlantic where finding them was tougher than finding a needle in a haystack. This would allow the allies some comfort although it was certain from the first day that they wont be able to hunt all of those submarines and some would surely pass through and complete their missions.
Over the years the importance of these sensors went down as Soviets built newer SSBNs with SLBMs which could strike America while they were in Barents sea or in the Arctic. Secondly the Soviets learnt about them and used various tactics to avoid detection for eg, sailing beneath a commercial vessel or using alternative paths through the Arctic. After the end of cold war these sensors are used for research on marine mammals which are acoustically pretty active although some are still used for their original purpose.