Royal Navy Sub Appears In Gibraltar Equipped With A Wake Detection System
This non-acoustic sensor could supplement the boat's sonar when hunting for especially quiet enemy submarines.
The U.K. Royal Navy’s Trafalgar-class attack submarine HMS Talent has emerged in the British territory of Gibraltar equipped with what appears to be a specialized system to detect hostile subs without using sonar. The concept of using various sensors to pick up the non-acoustic signatures of other submarines is hardly new, but Talent’s added equipment follows years of reports of increasing underwater activity from potential opponents, such as Russia and China, in both the Atlantic and the Pacific, among other bodies of water. It also comes as both of those countries continue to develop and deploy quieter nuclear-powered and advanced diesel-electric subs.
Photographer David Parody grabbed some great pictures of Talent as she entered the Bay of Gibraltar on May 8, 2019. Observers were quick to spot the never before seen piece of equipment on top of the forward hull. Parody subsequently found another picture of the same boat from April 2019, showing the system installed. However, he said she had lacked the apparent sensor arrangement during another visit in 2018, which followed an extensive refit, suggesting the addition was relatively recent.
It’s not clear whether the new addition is permanent, either. Talent is the second to last of the Trafalgar-class submarines, having gotten commissioned in 1990, and one of only three of them left in service. The Royal Navy plans to decommission her in 2021 as it phases out the entire class in favor of the newer Astute-class.
The system has four individual probes in front and is visually reminiscent of features most commonly seen on multiple types of Soviet and now Russian submarines. Though there are various different configurations with their own specific nomenclature, these are commonly referred to collectively as System Obnarujenia Kilvaternovo Sleda (SOKS), which translates Wake Object Detection System. SOKS allows these submarines to detect underwater opponents without using sonar, but more on that later.
Long the default for submarine warfare, sonar still has certain limitations. Modern sonar systems typically have both active and passive functionality. In their active mode, they operate similarly to radar above the waves, but use acoustic energy instead of RF energy, sending out “pings” that then bounce off objects undersea and on the surface. The passive functionality gives operators the option to just listen for certain noises in relation to their surroundings using the system’s highly sensitive and largely omnidirectional receivers.
However, active sonar can quickly give away a submarine’s position, while the passive mode may pick up all manner of background sounds and is impacted by the constantly changing ocean environment around the submarine. The two videos below give a good sense of the factors involved.
The thing is, staying silent is essential to a submarine’s survival. Over the years, major navies around the world have invested significant time and resources into the development of quieter types, using either nuclear powerplants or diesel-electric systems with advanced air-independent propulsion (AIP) systems, among a host of other sound-dampening features.
Trying to "hear" the most advanced designs using passive sonar could be especially difficult and "pinging" with active sonar might often be too risky an option. This is where systems such as SOKS come in.
There is very little hard detail on exactly how these systems work, but the name seems to make clear that they at least have the ability to sense changes in water density that submarines make as they sail underwater. A number of modern torpedoes use guidance systems with similar “wake-homing” technology to find their targets without relying on their own sonars, which can get jammed or confused by decoys.
But reports say that components of SOKS may also be able to pick up various chemicals that submarines leave in their wakes, including temporary anti-corrosive coatings and byproducts from oxygen generation systems. They may also be able to pick up minute amounts of radiation from nuclear-powered submarines or detect the slight warming of patches of water from being in contact with a warmer submarine.
The United States first became aware of SOKS in 1969, when it spotted K-14, a November-class nuclear-attack submarine, equipped with an early version of the system. Still, by the 1970s, American intelligence agencies, including the Central Intelligence Agency, were dismissive about its potential capabilities, suggesting it had extremely limited range and sensitivity. As late as the 1990s, at least some members of the U.S. military were still of the opinion that “whether or not hydrodynamic phenomena [wakes] are exploitable is open to question.”
The U.S. Navy had itself explored many of these techniques around the same time to Soviets did, but abandoned them in favor of advances in sonar. The Soviet Union was not making the same kind of progress in sonar, forcing them to explore alternatives.
But the persistence of SOKS in Russian Navy service suggests there have been meaningful advances in this technology. The U.S. Defense Advanced Research Projects Agency (DARPA), as well as Chinese research institutions, have also been re-evaluating sonar alternatives more recently, which only further supports this conclusion.
Improvements in sensor technology, real-time processing, and raw computing power could certainly have helped make these sorts of non-acoustic systems more practical. Just like sonar systems, SOKS and similar equipment would still need very specific processing systems to be able to help separate the signature of an enemy submarine from any naturally occurring chemical concentrations and hydrodynamic phenomena and provide operators with reliable information. One can imagine that by sampling the water for a number of submarine-related anomalies, a system could give crews a better idea of the likelihood that a real submarine has been detected and it could possibly help classify the target based on a library of sample data. Once detection occurs, tracking is also a real possibility. The system could also be used for tracking alone, once a target is detected by other means.
The Royal Navy’s outfitting of Talent with what appears to be non-acoustic sensors isn’t even the first time a Trafalgar-class submarine has emerged with such a system, either. Another Trafalgar-class boat had appeared in the past with a similar set of equipment mounted on the front and sides of her sail.
This is not necessarily surprising. Since at least 2017, there has been a steady flow of reports from the U.S. military and NATO members highlighting increased Russian Chinese submarine activity in both the Atlantic and Pacific. The Russians have also notably increased their underwater operations in the Arctic region, as well as in the Mediterranean Sea and Baltic Sea. At the same time, both countries have been working hard to expand the size, scope, and capabilities of their submarine fleets.
None of this is to say that sonar is in danger of going away, but it may be increasingly the case that submarines will have to rely on a broader array of sensors to find their targets or avoid enemy threats. The non-acoustic component could serve as a short-range tool for silently keeping tabs on a target submarine and potentially allow operators to identify and log specific signatures in the process.
All told, Talent’s new equipment may stand out now as unusual, but there could be a growing demand for non-acoustic sensors as time goes on, especially if the technology has truly proven itself to be mature and reliable.
Correction: The original version of this story said that there were four Trafalgar-class submarines still in service, when there are only three at present. It also said that HMS Trafalgar had appeared with a different apparent wake-homing system in 2018, when that submarine was out of service in 2009.
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