The arrival of HMS Talent in Gibraltar in February fitted with additional sensors on her fin has raised the public awareness of non-acoustic submarine detection methods. Sonar remains the primary means of locating submarines but here we examine what is known about other technologies that may be used in the undersea battle to detect and trail adversary boats.
In ‘conventional’ anti-submarine warfare submarines are usually located acoustically, either via active sonar that requires the hunter to send out a sound wave, which hits the target and bounces back, or passive sonar that simply listens for noise radiated by the target. As sound waves can travel very long distances through water it is the primary means by which submerged submarines understand their environment and hunt their prey. Sonar has its limitations and other passive methods of detecting submarines would be extremely useful. Wake detection systems may rely on finding traces of either heat, radiation, chemicals or bubbles left by the submarine as it passes through water as well as disturbance to the water itself. These faint signatures may be left behind for some hours after the submarine has passed by and offers a means to trail boats that may be used to supplement acoustic methods. With sophisticated analysis of the data generated by the sensors it may also be possible to determine the direction of travel, speed and distance travelled by the boat.
Any articles in the public domain on this subject must rely on non-classified sources and information is understandably limited. Wake-detection and similar technologies for civilian use able to sense exceptionally small amounts of impurities in water is a highly technical subject and the science that underpins it continues to advance.
The Red’s SOKS
The Soviet navy appears to have been the first to develop wake detection systems. The Systema Obnaruzhenya Kilvaternogo Sleda (SOKS) was developed in the late 1960s. During the later part of the Cold War it became known that Soviet submarines had managed to trail NATO boats undetected on a few occasions. The Russians confirmed this publicly in the 1980s, claiming that the Victor class boat, K-147 had followed an American SSBN (probably USS Simon Bolivar) for 6 days. Western sonars and submarine silencing capability was known to be considerably ahead of the Russians and NATO boats routinely tracked them for long periods using passive sonar only. Initially, analysts considered it almost impossible the Russians had managed this and were at a loss to understand how this might have been achieved.
An investigation by the CIA concluded by the early 1970s that wake-detection technology had been used. The Soviets had succeeded in creating a variety of sensors that could be used operationally, given the right circumstances. The USN had explored similar technology in the 1960s but had abandoned it, putting all its effort into improving sonar capabilities where it enjoyed technical superiority and the huge advantage provided by the SOSUS seabed array system.
Russia has continued an iterative development process for SOKS with systems code-named by NATO including Kaira (1978), Bullfinch-2 (1979), Toucan-1 (1981) and Ear (1982). The investment in this technology over many years suggests it has matured to be a reliable and useful system and its use is part of Russian operational doctrine. Their modern Akula and Yassen class SSNs are equipped with the latest versions.
Royal Navy not out-done
Surprisingly, there is more is in the public domain about Soviet and Russian systems than about UK wake-detection technology. What is certain is that RN submarines have received various Non-Acoustic Sensors (NAS) for trials and testing going back at least three decades. Whether used operationally across the fleet or on a temporary experimental basis is unclear. The UK has a reputation for excellence in sonar research and manufacture. The highly sophisticated Sonar 2076 suite fitted to the Trafalgar and Astute class is reputedly one of the best in the world but the RN still considered it prudent to pursue other detection technologies.
HMS Trafalgar was fitted with NAS sometime around 2004-5 and at least part of the equipment remained mounted until she decommissioned in 2009. Around the same time, HMS Torbay also received additional sensors mounted the port side of her fin (but this appears to have been removed by about 2010). During this period, Torbay also sported an experimental navy blue paint scheme intended to reduce the visibility of the boat at shallow depths when operating in the blue waters of the Mediterranean. Torbay was eventually repainted in the traditional pusser’s ‘North Atlantic dark grey’ but HMS Trenchant emerged from a very long refit in 2017 with the dark blue paint scheme.
Until the reappearance of the probes fitted to HMS Talent in 2019, this is all that can be said with certainty about modifications to the Trafalgar class boats through observing visible external additions. Other boats may have had less obvious equipment fits, either retractable probes or housed within the casing, the fin or mounted below the waterline. It is possible that the Astute-class boats were designed to carry NAS integrated from the outset and the sensors are hidden from view, although this is only speculation.
Hunting without sound
Details of how the non-acoustic sensors work are sketchy but in broad terms, infrared or laser light is passed through the water being sampled by the probes. The absorption or refraction of light by tiny particles present in the water can be measured. The science of spectroscopy enables the detection of very low concentrations that may only be a few parts per billion. Small changes in salinity, temperature and density may also be measured. The sensors may take thousands of samples per second which require computers to process the stream of data to distinguish between naturally occurring phenomenon and the distinct signatures left behind by a submarine.
The wake of a submerged submarine naturally spreads out over time which offers a sporting chance of locating it in the first place. The sensors on a single submarine are relatively close together and likely to distinguish only between actually being in or out of the wake. The needs for multiple sensors arranged it different places on the hull is to confirm the wake is being detected and it not just one probe getting a false reading. The different shaped probes are likely optimised to sense different properties of the wake. Just as sonar propagation is affected by environmental conditions in different parts of the ocean, non-acoustic sensors may also be hampered by factors such as salinity, pollutants, strong currents and water disturbed by other vessels, particularly in shallow and busy littoral waters.
Radiation. Nuclear submarines have many tactical advantages over conventional boats but emit a very faint but distinctive radioactive signature. Radionuclides are a by-product of the nuclear fission process and other radioactive elements will be left behind by an SSN or SSBN.
Heat. Nuclear submarines use large quantities of seawater to condense the superheated steam and cool the reactor. It may be possible to detect the trail of slightly warmer water pumped out by the submarine for some hours after it has passed by, although the effectiveness of this method could vary greatly depending on the ambient sea temperature.
Both radiation and heat detection methods are not applicable to conventional submarines. Russia’s newer Kilo and Lada class boats (Project 636, 636М and 677) are exceptionally quiet SSKs, hard to detect with passive sonar and are known to be active in the Eastern Mediterranean. The RN’s non-acoustic sensor outfit would be particularly useful against these targets so radiation and heat detection is unlikely to be of prime importance.
Chemicals. A vessel passing through water will leave a distinct chemical trail behind it. This may include tiny particles of paint, rust and zinc from the sacrificial anodes fitted to reduce corrosion. Hydrogen is a by-product of the system used to make oxygen for the submarine’s crew to breathe and is detectable when dissolved in seawater. Some of this chemical trail may be reduced by careful design and use of materials but it is almost impossible to eliminate entirely.
Bubbles and waves. All moving submarines leave a trail of small bubbles behind them. Great efforts have been devoted to reducing the cavitation effects of submarine propellers through careful design, high precision manufacturing and polishing. The rapid changes of pressure in the water around the rotating propeller or propulsor lead to the formation of small vapour-filled bubbles at the blade tip which then collapse, creating unwanted noise. Shrouded propulsors with large, slow-turning rotors have helped reduce cavitation and radiated noise but bubbles will still be formed, especially at higher speeds. Tiny bubbles remain present in the water column for some time. It may also be possible to detect the movement of the water disturbed by the passage of the submarine. The waves and eddies may linger in the water column and the tiny variations in pressure may be detectable long after the submarine has gone. Theses signature are likely the most important method of non-acoustic submarine detection.
Talent gets toys
Sometime in 2019, HMS Talent was fitted with a wake detection system on the forward part of the casing. The visible mounting consists of 4 probes. This was further supplemented with another two identical mountings fitted on either side of the upper fin in 2020. The reappearance of NAS on a Trafalgar class boat suggests that the technology is continuing to improve, investment is ongoing and its tactical value is worth pursuing. Open-source information from the civilian industry indicates that similar particle-in-water sensors are becoming more accurate and compact. Perhaps of greater significance are the advances in artificial intelligence and machine learning. Computers can be ‘trained’ to search for very specific patterns buried in huge amounts of data that are the unique tell-tales indicating the presence of a submarine, while eliminating false positives. Not only is vastly more computing power available relatively cheaply, but these new processing techniques can quickly make sense of the data stream from the sensors, and provide the submarine commander with more reliable guidance for trailing a submerged submarine.
If a submarine cannot be detected by passive means, resort to active sonar is usually undesirable. Going active will immediately alert the prey that they have been detected. Active sonar provides bearing and range data but also reveals the same information to the target, potentially allowing its adversary to achieve a fire-control solution, should it wish to launch a torpedo. NAS are far from a panacea that will allow all submarines to be instantly detected but is another tool that may be integrated with the conventional sonar picture. NAS could be used to confirm fleeting contacts from passive sonar or localise a target when cued into the general area by intelligence from other sources. Above all, NAS appears to be ideal for trailing a very quiet SSK at medium or short range. Faced with a proliferating conventional submarine threat, the RN’s small SSN force needs every possible sensing advantage that can get, although well trained, experienced and canny submariners are still the most important element of success.
As the penultimate Trafalgar class boat, HMS Talent was originally scheduled to decommission this year but the lives of the three remaining T-boats have been extended by at least 2-3 years. HMS Trenchant was due to go in 2019 but is still going strong. Delays to the Astute class service entering service have left little choice but to invest further in maintaining and updating the venerable T-boats, that despite their age, are such an effective platform that they can still hold their own in the 2020s.
The NAS discussed in this article are carried by submarines to detect other submarines but there is a whole other branch of scientific investigation dedicated to finding submerged targets from the air or by satellite using non-acoustic means. Despite many decades of supposed scientific breakthroughs that claim to “make the seas transparent” using radar, magnetism, lasers or optical detection methods, the submariner community remains highly sceptical as none have been yet been fully proven to work operationally. Wake detection has been around for some decades and there are operational torpedoes that use this guidance method (The larger bubbles and more obvious wake of a surface ship is much easier to track than the discrete signature of a submarine). NAS clearly continue to have significant and improving utility in the undersea battle and it is interesting to speculate about how other nations besides Russia and the UK may also have developed this technology.
(Main image: Moses Anhory, via Flickr)
What are the tiles all over the boat used for? Dampening sound reflection? Insulation?
Yes – anechoic tiles are rubber or synthetic polymer tiles used to absorb active sonar waves and reduce radiated sound from inside the submarine. They are glued on but frequently a few fall off leaving the gaps visible in some images.
It’s a shame our Trident and trafalgar class Subs have so many Tiles missing Ut still go to sea,… The Submarine tiles Tech was an amazing advance…
So, Russki wake detection use anechoic tiles detection in wake of the boat (They fall slowly to the bottom) And/or by missing anechoic tiles detection (micro-turbulences and dissimetric noises port starboard sides).
Two new episodes for Tom Clancy…
Its so hard to get a good tiler these days. I’ve been waiting for months for a bloke to turn up and finish the tiling job in my bathroom.
I’m a roof tiler, but my mate dave does bathroom tiles ?
Interesting, I wonder what techniques they are using.
There are also lasers, magnetic detectors and sniffers for combustion detection.
It has been a widening field (sorry for the science joke I’ll get my coat). If you look at the small modules that have been added to laboratory instruments (Hewlett Packard and Varian lead the early manufacturers) to to HPLC-MS etc since the early 90’s it will give a good clue as to what is possible. None of that is even vaguely secret as it is in the manufactures online catalogues.
It is just standard laboratory analytical tech that has been optimised for the job.
The early Russian efforts were very clever but needed quite a lot of space as ‘compact’ was not the operational word.
As ever getting a lab concept to work in the ocean would be interesting.
Thanks for those good hints. I was thinking the other day about MRI technology as used in hospitals, its sensitive enough to detect the small changes in inter molecular bonds in water molecules in the human body ( I hope thats what I think it does) Maybe some adaptation of the tech can find water molecule bonds altered by the nuclear submarines condensors or even the large electric motor magnets ? Im being very speculative here
MRI -> NMR (NMR is the big brother of MRI) tech isn’t sensitive enough unless you are using very high fields and superconducting probes. I can’t really see how you could fit that on a submarine. I still think there would be a few zeros adrift even then.
NMR (MRI) looks at proton nucleus spins. Known as nuclear magnets. So, yes, it is a very sensitive technique for looking looking at magnetism *in very restricted* circumstances.
You could, perhaps, use stop flow HPLC-NMR to concentrate the samples.
Things like HPLC-MS (mass spectrometry) are orders of magnitude more sensitive. Mass Spectrometry can pick up changes in isotopic ratios.
Generally you use hyphenated techniques to enhance complex detection and sometimes to concentrate samples.
That is all in postgrad textbooks from the 2000’s and earlier.
As regards stray field perturbations from motors these have been well screened out, actively for years. Look at Ultra Electronics website. The thing is this stuff is easy to measure so you can engineer it out. You *might* be able to detect artefacts from the cancellation systems if you knew exactly what you were looking for. But I doubt it.
You are not going to reproduce on a submarine something more sensitive than the best university lab instruments which are mounted on massive concrete slabs in controlled environments…..
I was wondering if they might be using a development of ISE technology for continuous flow monitoring.
Have a look at
These guys are the very best at the sort of sensor tech we are talking about.
It seems strange that in this day and age with the tech available, the sonar readings look so primitive. Why haven’t we developed “visual sonar” showing a picturial view of the sonar return based upon a HD comparison of returns interpreted by an AI system.
These are reality and have been for some time.
They can be done from multiple sources to produced HD 3D views of air/sea whatever if you have a the sensors available. Input from Sonar/sonar buoys/helicopters with dipping sonar can all be melded together into one view.
Equally for radar/lidar.
The best are composite: bringing loads of systems together. You can’t fool all of the sensors all of the time.
Nice to see an old friend still leading the way. 🙂
It certainly is, she’s getting a tad old now though!?
I remember her when she was new. :0
So do I, are we talking commissioning!
Not far after….
I took her out of build and then did a few years before moving on to bombers would you believe. Got the shock of my life when joing them, totally different way of doing things.
I’m looking at her sisters rotting away in port….
Excellent article. Just mentioned in the final para, but I recall wake homing torpedoes being developed in the latter part of WW2, not sure exactly the technologies involved in that as computer analysis would not have been available?
Purely acoustic technology: homed in on the highest sound pressure levels.
Easily spoofed as all you needed was a louder sound.
As they became, relatively, more sophisticated settable notch/band pass filters could be adjusted to the likely frequency range of sound as detected by the passive sonar.
That was before digital lookup tables existed……
They weren’t wake himing, they were acoustic (the G7e from Germany and T24 ‘Mine’ from the US). The Wake Homing torps were first deployed by the Soviets late in the Cold War.
Yes. Thats homing on on the noise of the propeller.
The Russians favoured the wake homers because of the large wake of US carriers when at speed and their 65cm torpedoes could be fired a long distance away and travel at 50 kt over more than 50km.
The US now has its small anti-torpedo torpedoes being installed on its carriers to counter this form of attack
Can anyone advise, what is the hump and dome on the rear deck? I dont think the subs originally had them.
It’s a standalone sonar fit.
A great really informative article ?
I wonder if both HMS Talent & Triumph, lives could be extended, to be used to patrol the home waters?
She looks larger in a photo on the Clyde.
I doubt it. They are worn out. But that isn’t to say there isn’t a need for an SSK to patrol home waters. The 6/7 (eventually) SSN’s could be used in distant seas. Crewing an SSN is an issue too. We need something like 8 of these with a maximum crew of 35 but able to run with a lot less. Just under 2000 tonnes……
In my ideal but realistic (!) world we would be operating 8 A-boats, 8 ocean going SSK’s, and 4 1000 (smaller probably) for training.
Trouble is the number of dive cycles on the pressure hull and the sheer age of the systems. Getting spares is soon going to be an issue.
The North Sea and the Atlantic are not very benign environments so the whole sub would have to be in tip top condition.
Given the small fleet we now have, they will have been worked very hard. Problem is even refurbishing them: who can do it? Barrow is choka, can the refit complex handle a full reworking: don’t know. Then who is the design authority for what is effectively a new class? Do we risk creating an MRA4 submarine?
Don’t get me wrong: I’d love to see a 50% increase in our hunter killer fleet. 11-12 subs would give us the capacity to deal with the unexpected.
There must be a way of speeding up the slug like progress at Barrow so as to create more build capacity. Maybe that involves working on Fridays afternoons and other revolutionary stuff like that? It is pretty unusual in a big setup like that to be effectively working a four day week with little or no weekend working. Almost all big projects like that have some element of weekend working so that the critical path items are expedited.
The long lead time on steel and other high end fitting doesn’t help. New Labour interrupting the SSN drumbeat and then the Tories dithering over Dreadnought did a lot of ‘damage’ too. We most definitely need 8 A-boats.
Another factor in build times is the rate at which funding is available from HMG. If that is available and there is also some sense of urgency about delivering capability to the RN (seemingly absent in T26 also) then there would be some incentive to address the current almost surreal build times. Some sort of comparison is the average build time for the original RN SSBNs (Polaris) which was approx 4.5 years, icluding first of class. I accept the Dreadnoughts are much larger but based on info in the public domain, build time is going to be nearly 3x that.
Yes, you are right: this was less about delivering the capability needed than about smoothing cash flow curves to the minimum level of spend. This pushes up unit price as all the overheads and contract preliminaries will be charged on calendar days.
It is a new mindset:spend money faster to save money!!!
Yes indeed, and I remember a (rare) admission that slowing the drumbeat of the Astute program for the reasons you quote actually increased the total class spend by £1.6 billion, which would have given us the eighth boat with some left over. My background is in shipbuilding, mostly naval, and I never met a civil servant that understood this reality. The same sort of thinking pervades the thorny issue of cutting ship numbers to save money, so you get the T45 saga repeated ad infinitum.
I say we can afford these things. But HMG decides to spend the money elsewhere.
There’s another reason why the build times extend and it tends to be based on ToBA like arrangements. You can build quicker with more people, but if you have a fixed number of ships / boats to build then you end up with a hiatus when the current class is finished.
Now – normal shipyards are quite happy with that, because its an opportunity (build slot) to get more contracts in. Trouble is – if your only client has a fixed number of ships / boats in mind and you are too expensive to get export work, then you end up laying people off. That is precisely what happened in Barrow post V-boat and is the reason behind the comically long build time for T26.
The T31 programme seems to have been set up to try the alternate approach (rapid build time), but it then leaves Babcock looking for something afterwards.
Long build times are significantly more expensive in total (you tend to be paying the whole yard workforce for the duration) and you end up with equipment that has been in the yard store for years before being flashed up. The flip side is that short-term cash outflow is higher and if there’s a gap in orders you risk losing your workforce.
The curse of ToBA coupled with too small a fleet.
Let’s see how the T31 builds go: worth trying.
Hopefully they read the bit in the Parker report about keep building them (T31/T32) and selling them off without expensive refits.
Let’s hope they didn’t. It’s a bonkers idea and will never get past the Treasury.
For the sake of argument, the economics would go something like :
So what you’re saying to HMT is something like :
For a drumbeat of one ship added / retired every three years, we’d like you to give us £83M pa. Every three years we’ll give you back £70M saved / recouped – or ~£23M pa.
Or, for a drumbeat of one ship added / retired every year you give us £250M (three ships in build at a time) and we’ll give you £70M.
I can’t possibly imagine the response, even after “tax receipts, VAT, powerhouse, wibble”.
The £20M midlife refit after 12 years seems a tad optimistic.
You need a recertification docking every six years anyway.
Your refit costs will obviously rise with age. But won’t be a.million miles away on average.
Either way, lots of money asked for, not so much returned.
Another factor in build times is the rate at which funding is available from HMG.
Yes. As I said,
New Labour interrupting the SSN drumbeat and then the Tories dithering over Dreadnought did a lot of ‘damage’ too.
Yes I do wonder too if there was a sense of urgency about the build of Dreadnought if the build time would fall. New technology doesn’t seem to ease build times only increase them.
‘Drumbeat’ was interrupted before Blair came to power in May 97 (and likely continued previous spending plans till 98.)
The last 2 Trafalgar class was laid down in 86 and 87 which over lapped slightly to 4 Vanguard class in 86, 87, 91 , 93
Astute of course was laid down in 2001. If the ‘drumbeat’ had continued with the conservatives the next SSN class would have laid down by say 95 or 96….which didnt happen so there was a gap from 94 to 98 with no new boats laid down , which was significant in that era.
The real reason was likely the end of the cold war by 1990 and the downsizing of the RN
Yes you are right! 🙂
I is difficult to see how a submarine campaign would wok with a handful of nuclear submarines . Is there any relationship to the submarine campaigns of WW2 where the U- boats grew to near a 1000 and the USN ended the war in surplus at 250 . The RN ran a campaign in the confined Med’ with a significant fleet then in the Far East (as opposed to the Pacific) . There are lot of ships out there to sink and each one needs at least one torpedo or missile . The Russians have a significant number of diesel boats and scattered through out the world countries are maintaining perhaps three modern diesel boats — To move from Perth to Brisbane still takes significant time , matched by a surfaced diesel boat >This is rough and ready , but surely there will never be enough nuclear submarines to sink all the ships as in WW2 — is there a policy I have missed completely Peter
‘Trouble is the number of dive cycles on the pressure hull”
Nuclear boats dont really surface and dive on a regular cycle like an air breathing SSK might and the missile boats go down and stay down.
As for major refits , those arent done at Barrow – I dont think that place is chokka either – they are done at the Devonport dock yard
Any depth change – irrespective of surfacing or not – incurs pressure change, which incurs stress in pressure hull and any internal fluid system exposed to dive pressures.
Very interesting article. I have wondered how a wake detector works.
I was more taken with the (exceptionally fine) photograph of Talent displaying two GP machine guns going into Gibraltar. Makes one think.