Monday, May 9, 2016

Sea Hunter

DARPA is testing a large, unmanned sub-hunting surface vessel (USV) dubbed Sea Hunter (1).  This is an interesting concept and well worth the effort.  The vessel is a bit smaller than a Cyclone class patrol ship and is intended to track and trail submarines using on-board sonar.  It is capable of 27 kts and can operate up to Sea State 5 and survive up to Sea State 7.  Endurance is 70 days.  Cost is $20M.  The vessel is currently unarmed although adding weapons would, presumably, not be difficult.

The type of sonar(s) has not been specified and there is no indication whether it is active, passive, or both.  Note, though, that the size of the vessel is quite small.  Thus, the sonar will be small and not very powerful.  This means that the search volume will be correspondingly small.  This is not a vessel that's going to search and sanitize a thousand square miles every minute!  Lacking any definitive information, I see this as a somewhat more powerful, mobile sonobuoy but not much more.  Other than dumb luck, I don't know how it will acquire a target to track.

What’s interesting is to contemplate the intended mission.  From what little the Navy has revealed, the mission is to find and trail enemy submarines.  During peacetime, this is a good way to keep track of enemy submarine movements and, presumably, gather acoustic signatures data.  During war, the mission would presumably be the same (ignoring weaponization of the vessel), however, the usefulness becomes questionable in much the same way as the P-8.

These vessels are not claimed to be stealthy and they have no self-defense, whatsoever.  In fact, they're fairly large, as unmanned vessels go and, I would assume, quite readily detected.  In war, they would simply be floating targets and easily eliminated.  The obvious question, then, is what is the wartime role?

One can imagine swarms of these vessels sent to chokepoints to pick up submarine movements.  As long as the chokepoint is under friendly control this will work.  Conversely, sending swarms into enemy controlled air/water space would simply be throwing them away.  While the $20M price tag confers a degree of expendability, simply throwing them away is pointless.  Of course, if we were to build thousands of them, the price tag would come down somewhat, one would hope.

Perhaps the vessels can be used to scout ahead of ship movements although, again, how to keep them afloat in the face of enemy action is a mystery.

Further compounding the problem is the requirement to maintain contact with, and control of, the vessel.  As we’ve often discussed, in war the vessel will have to operate in a heavy ECM environment and the ability to maintain communication is suspect under those conditions.

Sea Hunter USV

As with the P-8, I’m missing the wartime role.

Another interesting aspect of the peacetime role is the unmanned nature.  Given China’s willingness to forcibly confront the US (EP-3 forcedown and various naval encounters) I strongly suspect that the Chinese won’t hesitate to sink these boats.  It’s quite easy to deny any knowledge of an unmanned vessel that vanishes at sea.  UAVs disappear all the time.  Why not USVs?  These vessels would also provide excellent live fire training exercises for Chinese submarines.  Not to neglect the Iranians, if they’re willing to seize US boats and crews, I can’t see them not seizing an unmanned, defenseless vessel.  I assume Russia and NKorea would similarly seize or destroy any vessels they find.  If deployed in this role, I suspect we’ll see large numbers of the vessels disappear for no apparent reason.

Looking at the broader picture, the third offset strategy championed by Bob Work is filled with this kind of highly questionable product that sounds good on paper but fails the test of combat logic.  We’re banking on a highly questionable strategy while conceding numerical superiority and quality.  That’s a good way to lose a future war.


(1)Breaking Defense website, " DSD Work Embraces DARPA's Robot Boat, Sea Hunter”, Sydney J. Freedberg Jr., April 07, 2016,


  1. There might be some advantage to having a sonar offset to allow a ship or aircraft to avoid a direct threat. Also, you might be able to send them places other assets can't go. If they are armed, I could see a group of them in choke points covered by an Arleigh Burke to extend its reach. I agree that sending them out far from help wouldn't be great unless you wer prepared to risk losing them.

    1. Look at the size of the ship. The sonar can't be very big or very powerful. Thus, it's likely a very short range sonar or it's passive. Lacking any definitive information, I see this as a somewhat bigger, mobile sonobuoy. This is not a unit that is going to sanitize a thousand square miles of ocean in two minutes while a destroyer sits comfortably out of range waiting for it to generate a target. Honestly, I have no idea how this thing would ever acquire a target other than by dumb luck.

      You make a great point about cost. They had better be cheap because most of them won't come back!

    2. What about a long tail? (I know nothing about what is necessary to stream these) but the SURTASS ships just used those passively to listen for subs at long ranges.

    3. I've seen no indication of any thing like that. The equipment to store, stream, and recover those is pretty substantial. I think well beyond the size of ship this is. The power required to tow something that's on the order of a mile long is immense - probably more than the vessel is capable of. The Navy fact sheet on SURTASS indicates a system weight of 140,000 lbs - again, probably well beyond the vessel's capability.

      Of course, a shorter tail is possible but then performance decreases as well. I just don't see this thing as having long distance sensing capability.

      Consider the passive sonar arrays on a Virginia class sub. They're large and they're spread along the entire length of the sub. There is no sign of any similar equipment on this vessel.

      I'm just not seeing the detection capability.

      We have a very difficult time holding contact on a sub even when using a Burke's large, powerful sonar, sophisticated computing, and manned interpretation. How is a tiny, underpowered, unmanned vessel going to accomplish that?

  2. Just thinking out loud...

    I've read its autonomous. If they could find a way to make them stealthy without too expensive, then I could see them as acting like a variant of the SURTASS ships.

    But communications would be a problem. Maybe they could record data to be sent by a burst via a timed buoy it could release, but that limits the data you can send, and its timing.

    If you could make it stealthy and weaponize it, then it becomes more interesting, but

    A) How much does that cost, and
    B) Do we really want a robot hunting automatically?

    1. "If they could find a way to make them stealthy without too expensive"
      "If you could make it stealthy and weaponize it, then it becomes more interesting"

      With ships, a large amount of stealth (but not the whole picture) is simply angling the hull inwards 10 degrees for everything under 20ft from the surface of the water and 15 degrees for everything above that.
      It's only part of the stealth picture, but it goes a long way and is relatively cheap.

      Suffice to say, a 'stealthed' version of this craft would actually not be that hard to design or that expensive to produce (still a noticeable bit more expensive than the base model), and any weapons you add on... quickly end up with a $100M+ hull.

      The stealthed version should be no more than $30M and adding $7 for at least a CIWS, maybe a little more for a few other things...
      Actually, you end up with a rather more deadly unmanned $50M PT/M Boat.
      ...that's not a bad idea, actually.
      Take out the unmanned aspect, give space for about 3-4 crew, and it gets better (~$20-23M for that).
      Massed Stealth, Low Riding Missile Boat Swarm. The fear of any modern CV fleet.
      (Classical Surface Action fleets with gun/AA heavy armaments had little to fear about that)

      But at this point, that's arguing doctrine, and we all know that the US' Naval Doctrine is flawed at the moment.

      - Ray D.

  3. Perhaps they'd be better sinking it so only an antenna was above the surface. Chuck some skis on it so that it could act like a hydrofoil to move quickly/avoid torpedoes - a bit like a flying fish!

    1. Sub-surface is not a bad thought. I wonder why they opted to make it a surface vessel?

      Good thought.

    2. A UUV would have even shorter range, speed and area search capability.

      Unless it was nuclear powered - which seems unlikely.

  4. because its cheap as chips. Thats why its a surface vessel.

    CNO. you simply can't state that.
    Do you know the physical dimensions of a large, or a small piece of sonar equipment, its a very powerful argument to be made from a point of ignorance when one states, "it looks too small".
    If theres someone who posts here that works with current gen sonars, i'd like to hear their opinion of what could be shoehorned into that hull.

    Also, not useless, not target practice, not floating missile fodder. Despite your not overly opinion of how navy does things, there are a bunch of Euro and Israeli firms building similar prototypes, so clearly, a bunch of defence companies all think this is the way to go.
    Swarms of these, even if moderately effective, will make life very vey hard for a modern submarine. Evasion wont even come into it, if you have 50 of them scouring a search area and converging on possible locations. In a data fused environment in conjunction with P8's generating leads, i think you'll find these will be horrendously effective against subs.

    As to weaponising, if Elbit can weaponise an 11 meter skiff with similar capabilities, then no doubt this craft will be sporting armament soon enough.

  5. All great points and great analysis by ComNavOps.

    The only thing I can think of adding is, I first read CNO comment about the article then read the actual article. What immediately jumped up was how everything was so positive in the article and pretty much how CNO took apart everything said in the article. I'm not expecting the author of the article to be so "pessimistic" (I can't think of the right word) as CNO but it makes me wonder about a few things....

    How much does the author knows about the system and it's utility, did the manufacturer release a press report and the author just copied it? (happens A LOT on Reuters by the way) and how objective is the author? If you are just Joe Public reading the article, you figure, USN got this thing all figured out and it's going to be super useful.....

    If no one asks the tough questions, is too afraid to rock the boat or just plain: "don't have a clue" and you are just filling up words on a computer screen so you get paid, lots of people are just going to assume the military "got this" and there's going to be a rude awakening one day.....just my 2 cents.

    1. ""pessimistic" (I can't think of the right word) as CNO "

      The word you're looking for is "realistic". Realism only sounds pessimistic to those living in fantasy land.

  6. Flaming datum remain datum.

    Given a choice between seeing a destroyer eliminated or and unmanned drove it's a easy choice isn't it?

    Simply forcing an enemy sub to destroy it is a highly valuable sacrifice move.

    1. How do you think we'll even know the vessel has been destroyed? I've read nothing that indicates that we will have constant comms with it - just the opposite. What I've read indicates that there only be occasional burst transmissions.

      As I understand it, these things will simply disappear and we'll never know why.

      In a war, most will probably be destroyed by aircraft and not become an ASW flaming datum.

    2. From the article it says that the plan is to have CONSTANT human supervision of the ship. Basically, it sounds like somebody gives the ship a mission, the ship thinks through how to perform the mission, and the person watches the ship's actions.

      "In fact, DARPA envisions constant human supervision for ACTUV. But it won’t be like a Predator drone, where a human constantly operates the unmanned system by remote control, Littlefield emphasized. Instead, the human will plan missions and issue general orders for the ACTUV to execute on its own, for example telling the vessel an area to sweep for enemy submarines."

      I think you have been way off base on your assessment of this ship.

      (1) You could use several of these to circle a carrier group to improve the ASW.

      (2) You could prevent submarines from transiting through the critical choke points along the first island chain.

      (3) Presumably, the navy will win sea control over large areas of ocean and these ships can help to protect against the submarine threat in areas we control.

      (4) These ships could provide a cost effective supplement that would improve ASW defenses for convoys or commercial shipping in a future conflict.

      (5) Expendable unmanned sensors that rack submarines provide a powerful force multiplier for ASW surface ships and ASW aircraft. The ACUTV's can be used to more aggressively seek out subs than expensive, manned platforms.

    3. I think it's important to emphasize that this ship is a demonstration project being run by DARPA. Critiquing the demonstration might be missing the a system like this would be used in the future is still to be determined. The emphasis should be on what technologies are demonstrated and matured that could then be applied to other applications or the follow-on vessels.

      I think this comment is spot on with the ASW screen idea and other concepts...picture every DDG-51 or other high end vessel having two or three of these buddy ships with the speed and endurance to keep up with the manned vessel. It could act as a forward scout extending sensor ranges or, when the shooting starts, turn on signature augmentation devices to be a sponge for incoming missiles/torpedoes. Or act as an HVU decoy.

      Another idea would be friendly port or choke point mine clearance to ensure that adversaries haven't covertly mined those locations to affect SLOC or flow of logistics ships. This would free up other mine hunting assets to work in forward locations. There really are so many ways that something like this could be used.


    4. "I think you have been way off base on your assessment of this ship.

      (1) You could use several of these to circle a carrier group to improve the ASW. "

      Just out of curiosity, how many square feet/miles do you think a carrier group occupies? I get the feeling that you think these vessels are going to present a "wall" of ASW. The reality is that each one is going to occupy a very, very tiny bit of ocean compared to the carrier group's footprint.

      Recall that the Perry FFG's were criticized for their weak, underpowered sonar which was considered nearly useless. This small sonar is not going to miraculously cover thousands of square miles of ocean. If the sonar were that good, we'd be frantically putting them in every ship we have. As I stated, this strikes me as a somewhat more powerful and mobile sonobuoy.

      While the article indicated that these vessels have a 20+ kt max speed, trying to operate around the periphery of a carrier group would require nearly constant max speeds which would probably take the endurance down to a few days.

      The vessels require radar to navigate, according to the article. Several such vessels, operating around a carrier group, with their radars broadcasting, would offer a enemy a pinpoint location of the group.

      As I said, as an experimental program, it's well worth playing around with but I get tired of seeing us spend time and effort on things that do not fit into any reasonable concept of combat. This vessel may or may not be combat-useful. I just hope someone has come up with at least a sketch of a CONOPS before committing money to the project. I'm neither for nor against this project - I'm just not seeing a reasonable combat use. Could it patrol around peripheral chokepoints? Maybe - and maybe that's sufficient to warrant investigation. Unfortunately, we seem to have a tendency to leap into technology development for its own sake rather than because it fills a combat need.

  7. Of course, leaving the US aside for a minute, not many countries can afford P-8s and the US needs its allies to fill a lot of the gaps.

  8. Time for some ACTUV basics, so you can make some good suggestion.

    1) The mission of Sea Hunter is to track small conventional Submarine, which normal operate were?

    2) The Sea Hunter will/is equipped with Raytheon new med Freq. sonar. It was based on SQS-56 I'm told.

    3)Stealth feature would be a waste on Sea Hunter for several reasons,
    3a) The Sea hunter navigates by Radar which operate all the time.
    3b) For safety reasons the Sea hunter is require to have radar reflector so other ship will sea it on their radars.
    3c) This way Sea Hunter look likes a civilian craft instead of a obvious military vessel.

    4) should we leave torpedoes laying around an unmanned ship without anyone to protect them from thieves


    1. "The Sea Hunter will/is equipped with Raytheon new med Freq. sonar. It was based on SQS-56 I'm told."

      I have not seen this. Do you have a reference?

    2. "The mission of Sea Hunter is to track small conventional Submarine, which normal operate were?"

      I have not seen this. Do you have a reference?

    3. "should we leave torpedoes laying around an unmanned ship without anyone to protect them from thieves "

      A very good point. Of course, one could also ask if we should leave our sonar sensor technology laying around for any country to seize.

    4. I would be surprised if various sonobuoys, seabed sensors and lost towed array fish haven't been picked up by other nations already but I agree that processing technology would be best kept off-board these boats.

    5. I got the information from were most of us get such information, from a Raytheon press release that some reporter rewrote to make his quota. I found it by Googling "ACTUV sonar". It pops right up.

    6. GLof, I'll check it out. Thanks!

    7. The vulnerability is another reason to keep the sonar equipment cheap and low end. However, our operation of these unmanned platforms during peacetime should be limited to prevent harassment problems.

  9. "The mission of Sea Hunter is to track small conventional Submarine, which normal operate were?"

    I have not seen this. Do you have a reference?


    This is a DARPA project, and the DARPA project web page calls out tracking SSKs.


    1. ip, nice. I hadn't seen that. Thanks!

  10. There has been a significant amount of discussion of what to do with the Sea Hunter concept, and it basically boils down to using this hull as an experimentation platform and helping inform what would be next. The algorithms for autonomous operation at sea can be proven out on earlier surrogate vessels and on the Sea Hunter, and then ported to other hulls of different sizes. Payload options and mission threads can be developed that would then inform what the next vessel would look like. Greater internal volume? Faster speeds? Longer ranges? The trades are nearly endless...

    One of the intriguing possibilities is mine warfare, in keeping with the mantra of getting the man out of the mine field. A vessel of this size and endurance could provide persistent search and engage capability, similar to using the MHU with the AQS-24 or the RMMV with the AQS-20, but also including a forward looking sonar (for near-surface detections in front of the hull) and some sort of neutralization capability.

    For ASW tracking, the track and trail is great for Phase 0 operations. The vessel could very well be lost as soon as the shooting starts, but under the CONOPS where this vessel trails the SSK during the SSK deployment, Blue forces maintain a constant awareness of the location of the SSK. P-3s / P-8s don't have that sort of endurance and require a hand off between platforms.


    1. Given how aggressive Iran, China, Russia, and NK are now, you don't see these vessels being routinely destroyed or seized even during peacetime?

    2. It’s a good question, and a question of what the perception would be to have a ship basically sitting on top of an SSK for a long duration and then what the response would be if that ship is sunk/seized. Is that considered an act of aggression with an in-kind response? This is really more of a philosophical discussion on the use of unmanned systems, and whether that use makes it more or less likely to engage in hostile acts.


    3. You bring up a very good point about the aggressive nature of having a USV trailing a sub. I'm sure we would not look too kindly on that being done to us. Of course, I would hope the part we would really be upset about is that someone was capable of tracking us!

      There is historical precedent for doing this. The Soviets routinely trailed our carriers and surface groups. Both we and the Soviets routinely attempted to trail each others subs with their own subs.

  11. I’ve actually played with this.

    Weirdly it was released by DARPA some time ago as a playable “game”.

    To try to learn how to find and track a target.

    It had people try to do it and was plugged into DARPA’s central computer to learn what it could.

    So it is semi-autonomous yes.

    If the “game” is anything to go by, you get assigned a square of ocean (seemed to be just off a coast) and you patrol it and track a sub. Id surface contact a sub surface vessels etc. etc.

    You got a basic surface radar, basic active and passive sonar, day night cameras, and range finder that kind of thing. Nothing amazing in terms of sensors really.

    Was a fairly boring “game”, but I see where they are going.

    I think the idea is that these things patrol an area ID ing transiting vessels and sub surface contacts, pretty much autonomously.

    If it ID’s a hostile, cannot ID a contact, is jammed or is destroyed a manned asset is dispatched. Otherwise it continues on its way.

    It’s a method by which you can cover a vast amount of ocean \ green water cheaply making the most of your expensive manned assets. The drone is considered essentially expendable.

    But presumably back up strike assets are going to be available to eliminate you should you touch it immediately. (So I’m assuming costal defence in the first instance)

    Actually I think its quite a nice idea, allowing us to address the declining hulls question, and effectively letting us be in many many places at once virtually. Deploying sparse hulls only where they are needed, when they are needed.

    I watch with interest.


    1. As I mentioned elsewhere, we seem to have very difficult times trying to find and track SSKs in exercises using our most sophisticated and powerful sonars, helos, and platforms - we generally fail, from what I understand. So, how do we think this small vessel with small, low power sonars, limited computing power, and no human assistance is going to do what our best platforms seem unable to do?

      This seems kind of analogous to saying that we can't see the enemies stealth aircraft with our most advanced radars so we'll send a drone with a $50 camera duct taped to it to monitor the stealth aircraft. Why would we think that would succeed?

    2. At the moment, and in my limited understanding, we find a submarine, positivly ID it at close range, and then move on, tracking it from long range, and if contact is lost, we return and using knowledge of its last confirmed position and speed, create a search area and find it again.

      If once a manned ship finds a submarine, it deploys a drone to sit above the submarine, it cant be lost until it returns to port.

      As you say, China would probably disappear them frequently, although thats easier in Chinas waters than the deep blue.
      Its (possibly) a handy method of making anything but coastal operations intolerably hard for China.

    3. CNO, you do have a good point.

      I think this is designed to be a defensive system only.

      Finding an SSK when its dug in on an enemies green water, parked up is very very hard. It’s performing area denial mission and exerting a threat over a much greater distance than its actual location, due to uncertainty.

      This model is to police surface transit vessels, and detect ANY transiting sub surface contact in the Green to Blue boundary. To defend against attack to our territory’s. Not attack theirs.

      SSK’s are unbelievably slow and limited range in blue water terms. The can only get to 20 knots for a very few hours ( say 4 ish ) and will then make noise. Your ability to actively ping them in this kind of environment really hampers their day.

      This thing doesn’t classify, it will just report and track a sub-surface contact until help arrives.

      Should they launch one of their limited weapons you defiantly have them.

      This is about producing these things in large expendable numbers to saturate areas. I quite liked the analogy of super mobile sonar buoys, that’s probably a close concept I think. That along with a coast guard \ patrol boat surface vessel ID’ing role.


  12. 1) A platform needs to be either survivable or expendable but not both. Letting manned ships be the former and unmanned ships the latter seems reasonable.

    2) Defensive measures are not usually a high priority on an experimental ship anyway.

    3) The sonar is apparently the Raytheon MS3, but details are skethcy

    4) Raytheon has a long history of putting their logo on european sonars, and charging a 500% markup. My guess is the sonar will turn out to look just like a Thales Bluewatcher or Kongsberg SS 2030. These are both relatively lightweight medium frequency sonars with some classification ability.

    5) Without a dipping or variable depth sonar the ACTUV will be handicapped in search, especially in the litorals where there are many shallow temperature gradients or pools of high salinity.

    1. Good contribution to the discussion!

    2. This sounds like more of a 'technology demonstrator'. I remember the SR-71 being introduced as the A-12 and being called 'an interceptor'. This might be a means for DARPA to justify seeing what this is capable of while trying to find a mission. Seems to me that an unmanned vehicle potentially hundreds or even thousands of miles away from 'home' would be subject to capture as well as outright destruction by someone not taking kindly to its presence. Also, to actually detect and trail and maintain that contact with a sub implies some degree of true artificial intelligence being on board, or at least constant radio and data link contact with a controlling entity, much like how drones in places like Afghanistan are often 'piloted' by personnel stateside. Lots of things to work out here.

      NOW, to me, what really makes sense and might be a more 'doable' mission in the short term is that of a mine hunting platform. Another possibility that comes to mind is that of a 'suicide' vehicle that can be directed or programmed to ram and explode against some types of an enemies shipping. How viable that last one is I'll leave to the experts, but given how all of us are GUESSING right now, and reacting to only what has been reported and released by DARPA, why can't those be possibilities?

      Doug in VA

  13. The important thing to remember here are the words "Test" & "Prototype". There are no contracts to build 50+ of these without any ideas on how they will be used or if their gear will work (unlike certain other ships).

    Randall Rapp


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