Monday, October 22, 2018

A Vision Of Future ASW

Anti-submarine warfare (ASW) always has been and always will be a challenging endeavor.  The submarine has the overwhelming inherent advantage.  It’s clear that surface forces (to include aircraft and ships) need a breakthrough technological and/or operational advantage to tip the scales back in their favor or even simply even them up a bit.  The problem is that most new technology is just enhancements of old technology: a sonar with better sensitivity, a variable depth sonar, a new P-8 Poseidon ASW aircraft to replace the old P-3, etc.  Even the latest concept of multi-static sonar is just an enhancement of normal sonar and has, thus far, proven generally ineffective.

The latest and hottest craze in ASW is unmanned vehicles.  Western militaries have gone absolutely “all in” on unmanned vehicles of every type and description and for almost every function in the military – and all without any substantive proof that unmanned vehicles are viable and effective in peer combat.  Sure, we’re all familiar with UAVs that shoot Hellfire missiles at some hapless terrorist but what about when we try to send that same UAV over the battlefield against Russia or China?  Odds are that the life span of that UAV will be measured in minutes. 

But, I digress …

I was talking about unmanned vehicles being the latest, hottest craze in ASW.  For example, the US military’s research group, DARPA, is developing an Anti-Submarine Warfare (ASW) Continuous Trail Unmanned Vessel (ACTUV) unmanned surface vessel that is supposed to trail submarines for weeks on end – without explaining how the small, low powered sonars on the unmanned vessel, with no human guidance, insight, or interpretation of data are going to effortlessly find and track submarines that full size, high powered sonars on manned destroyers that are also equipped with towed arrays and undersea warfare software suites can’t.

But, again, I digress …

Let’s move away from specifics and, instead, consider general concepts.  I came across the following description of one blogger’s vision of future ASW operations.  His vision illustrates the fascination with unmanned and beautifully captures the essence of what, I suspect, most people would see as a reasonable operational concept.  Here it is,

“So, a vision of near-future ASW could look like this.  Ahead of operations in a particular area, a number of autonomous underwater sensors are deployed, mapping the environment and generating an updated model of the sonar conditions that exist.  A force then moves into the area, screened by a number of USV’s [ed. unmanned surface vessels] deployed ahead of the force.  The escorts could search a huge front, with the USV’s up [front] and able to detect the SM [ed. submarine] before it can get into firing position and MPAs [ed. Maritime Patrol Aircraft], if available, would link into the network and add their own sonobuoy data.  Once detected, the SM is fixed and the force can deal with it however it wishes – surging helicopters or MPAs to harry the SM, or long-ranged engagements with a weapon such as ASROC.  It’s a worthwhile vision of how effective a Type 31 frigate could be if both it and two SEAGULLs [ed. a specific USV] were equipped with an interlinked system like TRAPS [ed. a type of variable depth sonar] and a weapon such as ASROC.” (1)

Note:  SEAGULL is a 12 meter long unmanned powerboat being developed by Elbit Systems

Note:  SM – I don’t know what that stands for as it wasn’t defined in the post but from the context it is clear that it refers to a submarine.

Well, that’s a very appealing scenario, isn’t it?  I’m betting most of you think it’s a pretty realistic vision.  Let’s take a closer look and see if its appeal holds up.

One fascinating aspect of the author’s vision is the battlefield preparation.  An unspecified, autonomous sensor is deployed in large numbers to map the battlefield and generate sonar models based on water conditions.  This is a great idea … if we know the battlefield ahead of time.  How often does a surface force have the luxury of knowing where an encounter with a submarine will occur?  Not often, bordering on never.

Yes, there are some areas such as navigational chokepoints where submarine contacts can be anticipated with some degree of likelihood but those are relatively few and such chokepoints are likely to be avoided by any surface force.  Beyond that, most encounters will be unexpected or only vaguely anticipated.

Thus, the ability to pre-deploy sensors is extremely limited.  ASW battlefields are going to be a surprise rather than planned.

The next aspect of the ASW vision is the employment of small, 12 m USVs with some sort of small sonar.  The vision anticipates these boats searching “a huge front” and detecting submarines before they can get into firing position.  Given that modern torpedoes have ranges of 20-30 miles (the Chinese Yu-6 torpedo is the equivalent of the US Mk48 and has a reported range of 28 miles), that means that the USVs would have to be deployed 25-35+ miles in front of the ships they’re escorting.  The area to be searched would, therefore, be 25-35+ miles in front and 25 miles or so to either side of the surface group’s path of travel.  That requires a search box perhaps 15 miles in depth and 50 miles wide, at a minimum.  That’s 750 sq. miles. 

Assuming a rate of advance of the surface group of 20 kts, the search box would also be advancing at a rate of 20 kts.  How many 12 m boats with small sonars would be required to search a 600 sq. mile box while advancing at a rate of 20 kts?  If a small boat with a small sonar had a field of view of 1 mile, it would require 25 boats in a line abreast advancing at 20 kts to maintain the search – and we’re ignoring the detrimental acoustic effect of the 20 kts speed on the boat’s sonar – hence the need for some depth in the search box to allow some sprint and drift type of tactic.

Where are 25 such boats going to come from?  A typical destroyer, for example, might be able to accommodate a couple of deployable small USV boats.  It would require 13 escort destroyers to carry and deploy 25 USVs!

Of course, we can manipulate the numbers by making different assumptions. 

This leads us to our next point of interest.  As we previously noted, if we’re going to believe that a handful of small boats are going to be effective then have to explain how our very best, highest powered sonars and towed arrays mounted on full size destroyers and operated by highly trained crew can’t find submarines with any significant degree of success but 12 m unmanned boats with tiny sonars powered by batteries are going to find submarines with unerring success.  If we actually had sonars that effective wouldn’t we be engaged in a crash program of retrofitting them to our existing destroyers?  Of course we would!  Since we’re not, it’s obvious that no small boat with a tiny battery powered sonar is going to find a submarine.

What becomes apparent is that such a boat is equivalent to a mobile sonobuoy.  Recognizing that, we see that such a small sonar CAN detect a submarine but the field of view is extremely limited (recall our earlier discussion about field of view and numbers).  Also, sonobuoys are static, once deployed.  As such, they are immune from self-generated acoustic “noise”, unlike the moving small boats which would likely be, essentially, deaf.

Perhaps we could deploy the small boats much farther in front – say, 30-50 miles.  That would allow some time to drift or move slowly while searching.  The problem there is how to get the boats there and then how to control/communicate with them since their communications are line-of-sight.  Communications limits the deployable distance to 20 miles, max – that’s not very far out in front and may not even exceed the operating host ship’s own sonar, depending on conditions.

Finally, note that the various platforms the author calls for in his scenario:

  • small unmanned boats,
  • an undefined field of autonomous sensors
  • maritime patrol aircraft
  • helos

What do these platforms have in common?  Answer: they’re all utterly defenseless and their effectiveness and survivability depends on the enemy offering absolutely no resistance.  So many modern US military (Western militaries, in general?) operational and tactical plans seem to depend heavily on the enemy’s cooperation.  For example, our plans to use UAVs and large, slow P-8 Poseidons depends on zero enemy opposition.  Would we allow the Chinese that kind of freedom to operate against us?  Of course not!  So, why do we persist in thinking the Chinese will allow us to freely operate all our shiny new toys?  I guess scenario planning is a lot easier when you start with the assumption that the enemy won’t do anything to hinder your actions!

Okay, I’ve critiqued the author’s vision of future ASW and without him being able to respond – an unfortunate and undesirable situation for which I apologize to the author – so what’s a better proposal?  Criticizing is fine but it’s preferable to offer an alternative at the same time.

We noted that ASW needs a breakthrough technology to level the battlefield.  Here’s some possibilities.

Unmanned “beaters” – torpedo-like vehicles that can travel ahead of a ship and carry active sonar.  The small size allows for many dozens to be carried on a ship as opposed to one or two unmanned surface boats.  The torpedo size/shape allows for simple launch from the host ship.  The purpose is less to detect a submarine than to flush a submarine from hiding.  The sub can either retreat – a mission kill – or attempt to close and risk increased odds of detection.

Wake Homing Anti-Submarine Torpedo – Submerged submarines leave wakes – large, long trails of turbulent, disturbed water which an ASW torpedo with a suitably designed sensor should be able to detect just as conventional wake homing torpedoes can detect surface ship wakes.  In fact, submarines impact their environment in many ways (thermal wake, Debye magnetic wake effect, eddies, chemical trails, minute radiation trails, etc. (2,3)) and those impacts can be sensed and tracked.  We need a brand new generation of homing technology based on previously impossible detection methods.

Limpet Particles – Small particles spread over large, suspect areas with properties of attachment and detectability.  Consider a submarine sailing through particle-seeded waters and slowly building up concentrations of attached particles that can be detected and tracked.  The attachment could be magnetic or some other attractive force that sea creatures would be immune to (it would do no good to track whales!).  The detection mechanism might be low level radiation, thermal due to induced friction, chemical (some unique, not naturally occurring chemical or isotope), or some other mechanism.

Penetrating Wavelengths – Acoustic wavelengths have been the traditional means to penetrate the protective water and detect subs but there is an entire spectrum of wavelengths that be able to penetrate water to useful depths.  Bear in mind that we don’t necessarily need to penetrate from the surface down to a thousand feet below the sea.  If the wavelength generator were mounted on a torpedo or some such device, the device itself could start at a hundred feet or a thousand.  The sensor would only need to penetrate the sphere immediately around itself to whatever range it can.

Bioluminescence – Many marine life forms generate light which is referred to as bioluminescence.  The passage of submarines disturbs the normal background light levels and studies have postulated the ability to find useful signals from the changes. (4)

Vortex – Similar in concept to wake detection, the vortices that submarines leave as the travel and maneuver can be tracked by mobile, underwater sensors.

And so on.

The purpose of this post is not to advocate for any specific technology but, rather, to note that we need to alter the current submarine/anti-submarine warfare balance which decidedly favors the submarine.  Unfortunately, with the end of the Cold War the Navy foolishly allowed its ASW capabilities and research to atrophy and we are now scrambling to catch up.  The Navy needs to begin conducting serious ASW research (not the warmed over obsolete version of ASW that they’re trying to install on the LCS but something truly effective) and developing new ASW tactics. 

We also need to cut the cord linking us so solidly to unmanned vehicles and expand our thinking to many other areas.  Until we do, submarines will continue to dominate the naval battlefield.


(1)Verdigris blog, “Unmanned Systems and Anti Submarine Warfare”, 30-Dec-2017,

(4)“The Anti-Submarine Warfare Potential of Bioluminescence Imaging”, Strand, Pautzke, and Mitchell, 1-Jan-1980,


  1. Great post, loads of questions.

    in my opinion we should be concentrating our unmanned development on mine clearance, I feel that will become productive quicker.

    I would suggest the US should purchase the UK Type 26 hull design rights and fit your own customer superstructure. (as Australia and Canada have/will).

    ASW is one of the few areas we still are world leaders in, even if we don't have the will to buy many (enough) hulls for the threat we face.
    This will speed up development time as the "super quiet" hull would take a long time to develop, especially as you don't have any recent experience of ASW hull design.

    Could also be used as your new Frigate.

    The cost will be high I hear everyone say, Well as far as I can see a tier 1 ASW asset that can keep up with a carrier group (and stay there in high sea states) is expensive, you pay for what you get.

    May be unmanned will work in time, but my bet is it wont be reliable until these ships are due for decommissioned.

    1. "super quiet" hull"

      I've not seen anything detailing hull/ASW design features. Do you have a link to anything?

      The old Spruance class ASW destroyer had acoustic isolation built in for its machinery along with Prairie/Masker and other quieting technologies. What does the Type 26 have?

    2. I dunno about the hull, but they are pricey about 2-3 times what Japan bought its Abukuma-class DEs for (depending on how you pick the exchange rates). In modern terms they a closer to the low cost ASW platform you like.

    3. The problem with one world class ship is if it follows a false alarm, than your one world class ship is doing that. If you could have 1-2 type 26s escorting a CV or 4-6 Abukuma class ships what would you pick. Recall its not like they need helicopters, the CV and it cruisers and Burkes have lots of those. Its not like they have anything better to do I mean the CV has the strike aircraft. And the Burkes and Ticonderoga are all super expensive to provide a supposedly huge anti-missile and anti-air umbrella.

    4. Try.

      Bit old but an ok description.

    5. This one isn't free. ://

  2. China recently announced a project to develop LIDAR that could detect a submarine at a depth to 500 meters. This would beat any detection device we have and catapult their ASW capability.

    While there is healthy skepticism that such a device is even possible, at the very least once again China's is spending money in moonshots projects that could leapfrog our planning and deployment strategies by decades.

    1. I mean, Northrop Grumman has a similar project developing a helicopter-mounted LIDAR pod, albeit the Airborne Laser Mine Detection System is supposed to be for minehunting missions. Still, I don't see why the research can't be leveraged and further developed into an ASW LIDAR system. Nobody remembers the 20mm m/42 recoilless rifle, and it wasn't much of a weapon tbh, but it was the stepping stone for Bofors to develop the Carl Gustav recoilless rifle that's a classic weapon in many armies.

  3. This comment has been removed by the author.

    1. Yes and the US has delightful stories about the F-35 as well. This the same China that will tell you all about their anti-ship ballistic missiles as well without ever demonstrating the ability to hit a drifting barge let alone a ship at sea.

  4. ....New means of detection.

    Historically new technology arrives with limited range. The bioluminescence, wake detection, MAD etc. all have a very short, nearly vertical detection range. Unless the Navy is willing to put dozens of aircraft (Bring back the S-3!) in the air, detection will be no better than the current technology. Off the top of my head, maybe a MAD sonobouy could be developed? It would be possible to drop hundreds in an area and they would function as long as the batteries lasted, at least several hours.

    I think the Navy should pursue a hi\lo mix of high tech Frigates and a "Fletcher" sized FF that is dedicated to ASW and can be built quickly and relatively cheaply. Numbers make a big difference in ASW. Building on a one-one basis with the FFG would increase the capability of the surface fleet.

    1. You've somewhat missed the point of the post.

      1. You're quite right that new technology is always very limited at first. One of the points of the post was that we allowed our ASW research to atrophy to the point of near non-existence. We should have been developing these technologies all along so that by now they'd be beyond the new and limited stage. This is a lesson we need to apply moving forward.

      2. Frigates (ASW vessels), while useful and desirable, are just more of the same and will not alter the fundamental ASW balance. We need them, certainly, until we can alter the balance but they, alone, won't alter it.

      The MAD sonobuoy is an interesting idea but it would require many tens of thousands to be used hundreds at a time, as you suggest. That, then, becomes a question of cost. They would have to be cheap enough to build in the many thousands and used as throwaway items.

  5. One area seagoing drones might be useful is as decoys. Enemy subs will be relying a lot on passive sonar to avoid detection. It’s easier to make noise than surpress noise. Have drone that put out the recorded sound of a merchant and heavy ships. Any enemy that takes the bait wastes a torpedo or two gives us a bearing. If they go active on sonar to confirm the target it gives away their position even more. Better to lose a half dozen $5 million dollar drones than ship with a billion dollars worth of war supplies.

    We once had a large passive sensor in SOSSUS.
    Presently the Chinese are putting acoustic sensors near US installations (with US academic assistance) obstensively for animal research.
    Perhaps the ocean near the Spratlys needs some purely peaceful sensors as well. Or we can lay some sensors attached to transpacific telecom cables as “maintenance” or

  6. One area have thought that might be worth researching is smell, the lemon shark can detect tuna oil at one part per 25 million, there are other examples of sea creatures using smell for hunting and finding mates, wandering albatrosses also follow their nose.

    Though zeo expertize and could be totally impractibile with current level of tech, but should be funding R&D to check out.

  7. Nice CNOPs, I agree. Let me tell you why.

    The physics of ASW havent changed much since the 1970s and 1980s. Sure, there is more computer power and digitization but the physics remain the same - active power or passive listening to detect, localize, track, attack, re-attack.
    The gear has improved though digitization/computer power but so has the enemy submarine- quiter and less apt to be detected active with anechoic coatings, etc. As a result those detection ranges- active or passive have not improved muc and the physoics of sound underwater has not changed. Sonobouys and active sensors are slightly more capable but the physics limit any gain..

    So were are we? IMO, the USN could last do ASW as a battlegroup or fleet around 1982-1992 and even then it was always dicey..

    There is nothing fundamentally wrong with our individual ASW assets today- P-8s, SH-60s, or our DDGS and especially our SSNs.

    The problem is:

    #1- we dont have enough stuff to really do ASW like 1990. We had 300 P-3s back then. Now 10 years from now we may have 108 P-8s...
    Obviously we dont have enough DDGs/SSNs either
    #2- we dont have S-3s anymore. This is a big defeficit bluewater and out of range for MPA.
    #3- No SOSUS or even towed variety..
    #4- and most importantly we dont TRAIN enough or with enough quality. ASW is an expensive team sport as is AAW and requires constant realistic training. Training costs big $$ and connot be simulated in a trainer mostlty. I saw the effects when ASW was bilged (defunded) as a USN mission during the 1990s.. As a result By 1994 every JTFEX run by C2F the enemy sub always won in the Gulf of Sabani requiring exercise reset! Spininnig off the S-3 from the BG was just one symptom of the loss of ASW...

    No marvelous new terchnology (especially unmanned ) on the horizon is going to make us better at ASW overnight or in the short term, lets say- 10 years. IMO we can only improve in the long term by going to back basics by first buying more stuff like more P-8s, adding a really persistant, manned, S-3 like vehicle to the CVN airwing and definetly buying more SSNs and DDGs. What about SOSUS and SURTASS? For the short term funding we need an immediate uptick for ASW training, training ranges, target subs and more/better ASW weapons (torps, depth bombs, standoff ). That will make a difference almost immediately; funding just "gimmicks" like the oxymoronic hi-alt ASW (cmon Man...), etc, of those drones-surf/subsurf will really make a difference.

  8. Relative to DARPA's ACTUV program, they are still at the prototype stage. I think there is some merit to the program and as with UAVs, it will take additional time to flesh out the concept and field a mature system.

    What would a mature ACTUV system look like and what could it do? My guess is a 1,200 to 1,500 ton ship with sonar and weapons (e.g., torpedoes, ASROC, etc.) that can stay at sea for 3-4 months at a time and is man-tended for at-sea replenishment and maintenance, with speed to keep up with a carrier group. And, has the ability to share data with ships, patrol aircraft and ASW helicopters.

    Such a ship then could act as the unmanned "beater" described in the post, but stay on station much longer and change its mode of operation. A group of such ships could act as a screeen for a carrier or amphibious group. Such a ship could provide long-term monitoring of major sea lanes and supplement port security forces.

    It's not a panacea or a miracle weapon, but we routinely use UAVs for reconnaissance and attacking targets on land, and it is time we do the same with surface ships.

  9. Agree with what B2.

    Every book on ASW since WW2 pretty much says the same thing: training and lots of it! All the fancy tech won't work and/or completely get swamped with false data, false contacts, biologicals,etc...and that's if all this super expensive gear survives contact with the enemy more than 5 still going to need somebody to interpret all the data, AI isn't going to be ready for many years.

  10. Ahoy ComNavOps,

    First I'll say I'm properly chuffed that you felt sufficiently strongly to write a full article based on my own. The whole point of my blog (limited though it may be) is to offer alternatives that aren't necessarily wholly realistic, but to set people thinking about how we might drive concepts and ideas forwards.

    The vision piece in my article was exactly that but I think it's more feasible than you might believe. I don't wish to write a full counterpoint, but I would like to expand slightly.

    The stimulus for the USV element of my thinking was a visit to Elbit Systems and a demonstration of their Seagull USV back in early 2017 - this also was the subject of my first blog article (link here I also gained much from a visit to NATO CMRE and saw their work - that's in the same article.

    I do think that the sort of USVs being scoped here have considerable potential over and above their smaller, battery-powered cousins. In the 12-15m length bracket, they are still small enough to be launched and recovered from larger vessels and, because they can use heavy-fuel engines and carry a decent amount of fuel, their endurance can realistically be estimated at around 4-6 days, even generating power for sensor systems.

    Moreover, those systems are much more capable than sonobuoys that you rightly compare them to. They are more akin to helicopter dipping sonars, and I have some experience as to how capable systems like the Thales Flash ADS are. Equally importantly, a USV can tow a decent sized passive array as well, which requires little power and can not only operate passively AND gather sound velocity profile data, but can also interact with other, active sources in a multistatic network.

    So in essence, I do see these sorts of USVs as having potential and see them as akin to a good dipping helicopter, only with less speed but greater endurance.

    Finally, I would politely challenge the effective range of adversary weapons. There are some very capable weapons out there as you point out, but the key issue is that unless you can see a target, you can't reliably shoot at it. Whilst a decent submarine might get enough information for a firing solution at 20nm against a noisy target, against a quiet target, or in the sorts of noisy, complex water columns we are talking about, that's a lot less. In fact, it's invariably close to visual ranges to get adequate target recognition whilst not forgetting that combat ID is essential. Equally, a torpedo has a far less capable sonar itself, so it won't be able to self-guide from maximum range, and 20nm-long wires, whilst possible, are so vulnerable to breakage that it makes the engagement far less worthwhile. Torpedo ranges are, in my view, far less about actual range than about endurance, the ability to chase about and acquire/reacquire its target through whatever decoys are sown. The greater endurance you put on your attacking weapon, the longer you keep your enemy on the defensive.

    I really enjoyed your article and thoroughly appreciated the opportunity to stimulate further discussion.

    1. Let me start by saying, welcome (I seem to recall a 'TAS' user from earlier times - maybe not you?), even if it's a good bit delayed!

      I'll repeat my apology from the post,

      "Okay, I’ve critiqued the author’s vision of future ASW and without him being able to respond – an unfortunate and undesirable situation for which I apologize to the author"

      That said, you didn't actually disagree with the post to any great extent! That's fine. In fact, your post succeeded admirably in your objective to "set people thinking about how we might drive concepts and ideas forwards" since it resulted in this post and the ideas that I offered which built off of your post.

      One aspect that you may be slightly overlooking is guided missile subs (SSGN). Torpedoes aren't the only submarine threat and, given the range of sub-launched anti-ship missiles, subs need to be detected as far away as possible.

      "a torpedo has a far less capable sonar itself, so it won't be able to self-guide from maximum range"

      In the sense that you're considering it, you're correct. However, wake homing torpedoes do, in fact, 'self-guide' and from extremely long range as long as they can find the wake. What that effective distance is, I don't know but it makes wake-homing a pretty effective 'area' launch weapon (less than perfectly precise targeting) from a substantial standoff distance. Notably, the US Navy has no effective defense against wake homing torpedoes. If you have more definitive data on wake homing performance, I'd love to see it!

      Feel free to comment extensively whether you agree or disagree with me!

    2. "properly chuffed"

      ????? Is that good or bad? I've never heard that expression.

    3. 'Chuffed', my friend, is a very British way of saying impressed.

      SSGNs are a good point to raise, but they are equally affected by targeting issues - they either need something to reliably target for them or have a good firing solution themselves. The trouble is, a good Russian SSGN is a capital asset and they aren't going to risk it unnecessarily. Getting something like that close enough to enable a comprehensive attack is risky - and we can shoot down missiles.

      Really enjoying paging through some of your back articles, keep up the good work!

    4. Feel free to offer a topic suggestion if there's something you think needs attention!

    5. "chuffed"

      What's that old saying? … Two nations divided by a common language!

    6. "a USV can tow a decent sized passive array"

      Where/how do you envision the analysis occurring? The two options would seem to be a fully automated analysis conducted onboard the USV with just the target location sent back to the mothership if/when such is found, or, the raw data is transmitted back to the mothership, continuously, and analyzed be personnel.

      The former option, full automation, would seem unlikely in that we currently, on full size, dedicated ASW vessels, require highly trained analysts to operate and interpret the data. If we can completely duplicate that capability in a single program on a small USV, then we're wasting a LOT of money operating ASW departments on larger ships and aircraft!

      The latter option, transmitting raw data back to the mothership, would seem undesirable in that it would require a constant, high bandwidth transmission that would seem susceptible to detection. Multiply that by however many USVs are needed to provide the requisite area coverage and the chance of detection also multiplies. Some type of narrow band, line-of-sight transmission could be used but that would limit the USVs to around 15 miles or less in front of the group.

      Any thoughts?

  11. There could be a relay USV to handle distance. As you would want the USV's towed arrays to become part of the ship's arrays the USV would pre process the data in case of immediate detection and pre process the data to send to the ship's acoustic computers to reduce bandwidth.

  12. The craze regarding unmanned everything seems...misplaced. I don't understand why the same task can't be accomplished cheaper and with no datalink issues by a manned 7 meter RHIB-type boat.


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