Monday, September 28, 2015

LCS Variable Depth Sonar

There have been several recent articles about the LCS ASW module being overweight and how it’s not really a problem and what amazing new capabilities the module will bring to ASW warfare.  Of course, the module consists of technology that’s been in use for years so it’s kind of hard to figure how the module will bring amazing new capabilities but that’s not the point of this post.  Further, the Navy assures us that modules diet plan to lose weight is not a problem.  Of course, the weight issues have been known for years and, presumably, the Navy has been attempting to lighten the module for quite a while now and this is the result.  This version is, one assumes, the lightest version that the Navy could assemble over the last couple of years of effort while still maintaining the requisite capability.  Thus, it’s hard to imagine where significant additional weight loss will come from without cutting into capability but, again, that’s not the point of this post, either.

Setting the preceding aside, the main component of the ASW module, such as it is, is the Thales CAPTAS 4 variable depth sonar (VDS) or a similar variant.  This, according to the Navy is an amazing piece of technology that will allow us to accomplish ASW feats never before seen.  Of course, the Thales VDS has been around and in use by foreign navies for years and the US Navy never before deemed it worthwhile.  Kind of makes you wonder, doesn’t it?

Be that as it may, if the VDS can add capability that’s a good thing.

What is it that makes the VDS useful over a conventional hull-mounted sonar, anyway?  Well, as the name implies, the VDS can be raised or lowered to any desired depth, somewhat akin to a helo’s dunking sonar.  This allows the sonar to listen under thermoclines.  Thermoclines are temperature gradients in the ocean that form layers.  The layers tend to reflect sound at the boundaries between layers.  Thus, sound at a lower layer can be trapped or channeled within that layer and not propagate to the layer above or below it.  A submarine can hide in a lower layer that a surface ship’s sonar can’t effectively penetrate.  Hence, the value of a VDS is that it can be lowered into a lower thermal layer and detect a sub that a ship with just a hull-mounted sonar can’t.

Which, again, begs the question, why hasn’t the Navy pursued VDS systems before?  I have no answer for that.  The old Soviet ships had VDS but I have no idea to what extent, if any, they were used.

Moving on …  Does the VDS bring with it any drawbacks or limitations?  As you might suspect from the question, the answer is yes. 

The first limitation is that the VDS requires around 20 minutes to deploy or retrieve.  Thus, the LCS can’t just hop around the liquid battlefield, nimbly racing to and fro collecting data.  Instead, it’s going to have to carefully pick its spots with the knowledge that once it commits to a spot, it will be there for an extended period.

Thales VDS

This leads to the second limitation and that is the vessel’s speed while the VDS is deployed.  The LCS was predicated on speed, speed, and more speed (not sure why but the Navy assures us that speed is critical).  Unfortunately, the VDS only functions at very low speed and, therefore, the LCS is limited to very low speed while the VDS is deployed.  Higher speeds will not only negate the VDS performance but may damage the unit if towed at too high a speed.  This presents a bit of a dilemma.  If the VDS is deployed and a torpedo is detected, the LCS can’t use its speed to escape.  It becomes a relatively immobile target.  On the other hand, if the LCS chooses to retain its speed capability, it can’t deploy the VDS and, thus, won’t be able to hear a sub or torpedo.  Hmm …  That’s a real Catch-22:  use the VDS and forfeit speed or use speed and forfeit the VDS.  The LCS can’t have both. 

Presumably, the Navy has already made the decision that the VDS is more important than speed or else they would not have pursued the VDS option.  Of course, that leads one to wonder what use the Navy foresaw for speed in the first place.  But, I digress …

If the Navy is committed to using the VDS extensively, that implies that the LCS is no longer removed from the ASW battle.  Sonar performance in littoral waters tends to be short range.  Recall that the original LCS ASW concept called for remote unmanned vehicles and vast underwater sensor nets that would be deployed and allow the LCS to stand off from the actual ASW battlespace.  So, with the LCS now conceptually committed to up close and personal ASW battles, we have to wonder about the LCS’ suitability for such a role.  Lacking the built-in quieting that a purpose-designed ASW vessel would have and operating noisy waterjets would seem to put the LCS at an enormous tactical disadvantage in ASW operations.

All of this leads one to wonder how carefully the Navy thought out the revised ASW module concept.  Has anyone gamed out how a loud, speed impaired LCS with no ship-mounted ASW weapons will fare in an ASW battle?  I strongly suspect that the answer is no and that a lot of sailors will pay the price to find out that the LCS is unsuited for ASW work. 

The VDS was a knee jerk reaction to the abject failure of the original ASW module and was not well thought out.  The Navy has to start thinking ahead and ensuring that they have logical and viable concepts of operation before jumping into development paths that make little sense.


  1. What sort of ASW work do they want the LCS to perform? In the littorals it uses a VDS, but that has all the issues you mention. The ASW module also lists an MFTA; which I thought was generally a blue water sensor. But they don't list the LCS as doing blue water work?

    1. Littorals by nature would suggest anti-diesel/AIP submarine work.

      That would mean fighting second tier to "great power" type enemies that have a submarine force.

      That's also where diesels have an advantage.

  2. Weeeeeeeeeeeeeeeeeeell, everything you said is bang on, towed array of this kind have limitations.

    I have no idea what effect the pump jet will do for it, but I imagine not much good. That and the less than quiet hull design.

    The concept for RN vessels is that this type of array is supposed to guarantee the detection of a sub OUTSIDE the range at which a weapon can be launched.

    Then with a rough bearing you dispatch the helicopter to confirm and deploy weapons.

    I’ll be honest, I have no idea how well this will work in the littoral, I would imagine it would be very very challenging. No point what so ever in variable depth function except to keep it off the bottom, thermoclines as you pointed out tend to be a deep sea phenomenon.

    Good luck with it though; it’s a very nice piece of kit actually. I would imagine as an anti-sub escort it could function fairly well in deep water?

  3. Well, since its a modular setup, whatever sonar they go with has to go over the side which limits them to some type of towed or VDS sonar. and a towed array wouldn't be able to scan forward of the ship, which you can do if you drop the VDS down enough.

  4. If Donald Trump wants to find where to cut waste in the Budget have him fire all of PEO LCS (PAST AND present) and cancel the LCS program. Nothing is sometimes better than something that never works but promises to do so.

  5. The Knox Class Frigate I was on had a VDS. It was an AN/SQS-35(V) and you are right it took some time for it to be lowered and raised with at least 2 people back in the VDS room. There was an tail added to it which was suppose to make it very good in the passive mode

    I was not a sonar man so I don’t know the details but I can’t remember anytime we deployed the unit near the coast or in shallow water. It did at times restrict our speed and maneuverability but once again I don’t know the details or parameters

    The Navy then went to the AN/SQR-19 towed array on the Perry, Spruance and Burke class

  6. One other issue worth noting. CAPTAS-4 is a Low Frequency Active Sonar (LFAS). While it can operate passively, its claim to fame is active pinging. This is necessary because modern submarines don't emit enough noise under normal operations to be detected at useful standoff ranges.

    Of course active sonar is easily detectable by the submarine and anyone else in the vicinity.

    The tow body trails the ship by a significant distance, but it has to be relatively straight forward to plot roughly where the ship is, given a few LFAS pings. Thus even a quiet ship will give up some of its advantage when using the VDS in LFAS mode.

    CAPTAS can work as part of a multi-static solution, with several sonars either pinging or listening. In theory you could have one LCS pinging while others listen, but i'm not sure if we are pursuing this.

    1. Drawing on my scanty and old knowledge of ASW.... isn't that what we used to do even back in the 80's with things like the S3?

      Drop a crapload of Sonobuoys over a wide area and have the S3 read them and act/guide resources on their data the way an E2 reads and acts/ guides resources on the data it gets from its radome?

      I.E. the S3 is your wide area network that can direct discrete units (FFG's, helo's) to prosecute local blips?

  7. "...If the VDS is deployed and a torpedo is detected, the LCS can’t use its speed to escape."
    Likely there is a fast cable cutter to allow instant jettison for that instance. I would think the submarine would be the one to try and sneak away, rather than confim its location by firing a torpedo.

    1. Actually, I would think an SSK would consider it worthwhile to take a shot at an LCS. You either get a physical kill or, if there is a jettison option and the ship is forced to use it, a mission kill since the ship is now out of the submarine detection business (MFTA, notwithstanding, which has its own problems operating in shallow water).

    2. That's assuming that the LCS ends up being any good. If you're an SSK and you can simply evade the LCS and break off towards whatever its escorting, you might get more of an element of surprise as the main target isn't expecting to be hit because it hasn't heard any warnings from the LCS you just evaded.

  8. You mentioned the LCS has no ASW weapons. Will the LCS not even have torpedoes for the Helicopter to carry?


    1. The ship carries the torpedoes but has no tubes to launch them.

    2. We're better off installing life boat launchers than light weight torpedo tubes. LWTs are too short-ranged.

      VL-ASROC or something else is needed.

    3. I'm not an ASW expert but my best understanding is that shallow water ASW, unlike blue water ASW, is going to involve lots of very short range work as a result of both the characteristics of shallow water (noise, debris, seabed features, etc.) which will significantly degrade sonar performance and the extreme quieting inherent to SSKs. Thus, short range ASW weapons may turn out to be necessary. I've suggested a modernized Hedgehog system (the Russians have RBUs) as a hedge (no pun intended) against those unexpected short range encounters that may pop up with no warning.

      I hope we're conducting lots of shallow water ASW training but since we have no SSKs to train against and we terminated our SSK rental agreement, I'm sure we're not conducting any training at all.

      That said, we also need longer range ASW weapons, as you suggest.

    4. IMHO, shallow water ASW requires a different CONOPS than what LCS offers.

      Certainly shallow areas may demand shorter range weapons as well as more numerous platforms and sensors.

      However littoral ASW can encompass significant deep and medium dept areas. Just look at the depth profile of the South China Sea.

      There are significant areas deeper than 2000m.

    5. "... shallow water ASW requires a different CONOPS than what LCS offers."

      And that's the key issue and the key failing of the LCS - no CONOPS. Acknowledging that none of us really know exactly what type of ASW tactics are required for shallow water, all we can say is that the LCS seems wholly unsuited. The LCS concept of ASW ops should have been worked out in detail long before committing to a full production run of 55 units. Now, we have a ship that is unsuited for shallow water (or deep) ASW and no idea how to make it even marginally useful.

      From what I know, the only way the LCS can be even marginally useful at ASW is to operate in teams of three or four in order to provide sufficient helo coverage and sonar coverage without becoming a target themselves.

    6. Not specifically defending the LCS, but pretty much any viable ASW CONOPS will involve multiple ships, helicopters, friendly submarines, MPAs, fixed sensors, and so on.

      LCSes with CAPTAS-4/MFTA and helicopters can be useful additions to that team, but the combination hardly seems optimal.

    7. Going ship-to-sub in littorals with ANY ship is a very bad idea. The sub has all the advantages.

      The best way to tackle that problem is with lots of air assets (helo, MPA). A ship that was cheap and could accommodate multiple ASW helos would have been very useful.

  9. Well, at least with the RHIB back end they have something like that.

    I'm just very skeptical of the LCS as ASW platform. The VDS doesn't sound bad necessarily in shallow water, but the ship itself, without any standoff weapons...

    A) I don't know what effect this would have. But I've worked with (recreational) water jets alot and to my untrained ear they are generally loud as hell.

    B) The hull form is designed for speed, not quieting. I don't know if this means it can't run quietly, but...

    C) The base ship(s) were originally ferry's, IIRC. No quieting there. And they don't appear to have added any.

    The biggest thing that this might have for ASW is its Helo's, but if you compare it to a Perry it has the same amount of embarked helo's, (1, IIRC) but the ability to work with the helo's isn't native' its part of the module. So....

    the crew isn't going to be praticing with the ASW guys consistently. And it would seem for ASW anywhere to work, especially in shallow water, you need multiple ships with alot of practice working in teams just to cover all the square footage you need.


    THe LCS is performing its unspoken role: Get hulls into the fleet. I'm not actually averse to that if this was a super cheap hull designed to do super cheap things (presence. Drug interdiction. Anti piracy). But again, The advocates seem to say two different things.

    A) Its going to be a huge asset because it can do ASW/ MW/ ASuW for the real fleet, and B) it was never intended to really fight all that well alone (even though originally it was said that it would...).

    Its an instance where we'll get it, put it in situations for which its not optimized (ASW in the littorals), and end up paying a high price because its just not good at its job.


  10. "Which, again, begs the question, why hasn’t the Navy pursued VDS systems before?"

    CNO, almost every US navy destroyer since the Allen M. Sumners have had VDS (SQA-8 VDS Hoist-Transducer / SQA-10 VDS Hoist, retrofitted), and even some Fletchers got it.
    The Burkes for some reason only have Passive Towed Sonar... probably because ASW was the job of the Spru-cans (the Burkes are actually horrible ASW hulls, as we know. The Ticos are ironically much better for that role).

    IIRC, it's the Thales-type VDS that the US Navy has historically hated, you so much as look at them wrong and something breaks.

    - Ray D.

    1. Ray, the last US destroyer to mount a VDS was the Barry mod (Sherman class) from around the mid-60's, if I recall correctly.

    2. Guess everyone forgets about the 46 Knox class frigates. Vds and towed array

  11. I thought VDS was chosen for the LCS because that platform couldn't support the USN standard ASW configuration of hull mounted sonar and passive towed array.

    1. So, VDS represents just another indictment on the LCS specifically and the USN in general for its low prioritization of ASW.

    2. In some water colums, a VDS is superior to a hull mounted array. The advantage of a VDS is ability to get the source below the sonic layer depth. A hull mounted array can't do that.

    3. I thought a MFTA did that too though?

      Do they have helo's with dipping sonars that could do the same thing?

    4. CAPTAS-4 can be both active and passive. MFTA is passive only. CAPTAS-4 source levels are much higher than helo dipping sonars.

    5. MFTA is both passive and active.

    6. You are right, CNO. MFTA does have an active component. However in combined VDS/MFTA systems, I believe the VDS is the primary active component, and MFTA is the primary passive component.

  12. Do not understand why not using a variation of the Modular Multistatic Sonar System (M2S2) using the Horizontal Projector Array, HPA, developed in Canada by GD, Ultra & Raytheon for the Halifax class. Assume NIH.

    Single Towed Array including:-
    Low frequency active source
    Torpedo defense
    Passive array
    Directional receive array resolves left from right
    Does not need to be recovered then redeployed in sprint and drift as no drag from towed body.

    Advantages are the lower mass than the LM VLA and separate Thales VDS planned. One advantage of the Halifax class is the ability to use Raytheon hull mounted sonar in addition to the HPA as the LCS 50 knot hull designs preclude fitment


  13. Completely off topic from reading the Oct.1st 2015 GAO report on the Ford Aircraft Carriers. GAO-16-84T

    Two points not seen mentioned before.

    "the Joint Precision Approach and Landing System has been
    deferred from the first two ships (CVN 78 & 79), eventually it will have to be installed on them to accept the F-35 fighter."

    The CVN 79 'Post Shakedown Availability' planned to be completed end 2026

    Does this mean looking at approx. 2026 before the carriers can achieve FOC with the F-35C


    1. I think you're asking whether full operating capability won't be achieved until 2026 due to the JPALS delay? I don't think that's an issue. They can still land the old fashioned way (meaning the methodology in use today!). Thus, full capability with the F-35 can be achieved today (neglecting the F-35's own myriad problems!).


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