Thursday, June 8, 2017

The Modern Hedgehog

ComNavOps has called for the design and construction of a dedicated anti-submarine warfare (ASW) ship instead of a frigate.  The reason for this is that our current ASW vessel is the Burke class destroyer which costs $2B each, conservatively, and is far too expensive to risk playing tag with submarines, especially small, silent, non-nuclear shallow water subs.  Further, the Burkes are primarily anti-air warfare (AAW) vessels and do not train for ASW enough to be effective at it.  That leads to the situation of a poorly trained and very expensive ship being asked to conduct ASW against an enemy that possesses most of the inherent advantages to begin with.  We need an ASW vessel that is dedicated to ASW so that the ship and crew will be thoroughly trained and cheap enough to be expendable when playing tag with submarines.

However, in order to be effective, an ASW ship must have effective weapons.  Currently, for close range encounters, the US Navy has only the standard Mk32 triple torpedo tube system (12.75”, 324mm) which launches lightweight Mk 46, Mk 50, and Mk 54 torpedoes.  Unfortunately, these torpedoes have problems with their shallow water performance.  The Mk 54, in fact, was developed in response to an urgent operational need resulting from shallow water performance problems demonstrated by the Mk 50.  The Mk 54 has had its share of problems with DOT&E assessing it as “not operationally effective” in its 2014 Annual Report and states in the 2016 Annual Report that the Mk 54 “will remain not effective even with the Mod 1 fixes”.

The US Navy also has the vertical launch ASROC system but it is not a close range system.  It has a maximum range of 15 miles.  The minimum range is unknown but given that the weapon is a homing torpedo, it figures to be substantial.

Thus, the Navy’s only shipboard, close range ASW weapons are torpedoes which have faulty shallow water performance, are subject to minimum engagement limits, and are assessed as “not effective”. 

As subs have grown quieter and more advanced around the world, and as US Navy ASW proficiency has atrophied, the likelihood that we will have more late detection, close range, unexpected encounters has increased.  Further, shallow water ASW with its attendant noisy (poor sonar) conditions almost guarantees much closer detections.  We need a quick reaction, anti-submarine weapon for those surprise, close range encounters.  The Navy has had such weapons in the past but abandoned them with the advent of the ASW helicopter which was supposed to keep the ship at arm’s length from the submarine.  In deep water, this is a reasonably valid concept but not in shallow water which is likely to be the more common ASW arena in the future.

Close range ASW weapons of the past include the iconic depth charge of WWII and the Hedgehog which was a mortar system that launched contact fused charges a few hundred feet in front of the ship.  These weapons were eventually abandoned in favor of helicopters and homing torpedoes.

WWII Era Hedgehog

Today’s version of the Hedgehog was developed by the Soviet Navy and is called the RBU.  The RBU is a short range rocket launcher which fires high explosive charges with either contact or depth fusing.  The charges can be fired singly or in salvo.  The launcher comes in various sizes which differ in the number of launching barrels, typically 6-12.  Maximum range is 1000 yds – 6500 yds, depending on the version.  The launcher is moveable in train and elevation and is rapidly and automatically reloadable from an integrated hatch at the base.  Magazine capacity is up to around 100 reloads, depending on version.  RBU’s were standard on all Soviet warships.

Russian RBU-1000

The RBU offers the capability of instantaneous attacks against very close contacts.  The charges are immune to countermeasures and, in contact fuse mode, offer positive feedback on hits.  The “dumb” nature of the free-sinking charges ensures that they offer no threat to the launching ship unlike homing torpedoes which can target the launching ship.  To prevent self-targeting, torpedoes have minimum safe distance arming limits.  Unfortunately, the minimum arming distance precludes engagement within that range.  Thus, the Navy’s short range torpedo is not really short range or, rather, short range is a relative term.  I’ve been unable to find a citation for the minimum safe arming distance for US torpedoes.  Thus, an RBU can fill the gap between the minimum arming range of the torpedo and the ship.

An upgraded version of the RBU, the RPK-8, uses the RBU launcher with a 90R homing head charge which offers increased chance of a hit.  The homing search radius is 130 m and the effective range is 600-4300 m and effective depth is 1000 m (1).  Again, this demonstrates the drawback to homing capabilities in the form of minimum safe distance limits from the launch ship.  Still, this may represent a balance of close range and enhanced kill probability via homing.  The system is quick reaction with a combat ready time of 15 sec (1).

RBU rocket charges are also much cheaper and smaller than torpedoes which allows many more to be carried and used.  In combat, when many questionable contacts will be prosecuted (no Captain will risk not prosecuting a questionable contact that could turn out to be real), the ability to use cheap, plentiful charges rather than scarce, expensive torpedoes could be a welcome option.

Russian Parchim Class Corvette Firing RBU-6000

Surface ships engaged in shallow water ASW or merely operating in shallow water will likely find themselves in surprise, close range encounters with non-nuclear submarines and a short range, quick reaction ASW weapon could provide the defense needed to survive the encounter.  The small size and weight of the launcher makes it suitable for any ship and allows it to be added almost anywhere that a small deck penetration for the reloads can be accommodated.
The US Navy should give serious consideration to developing or obtaining such a weapon system.  The combination of a small, dedicated, cheap ASW vessel and basic, reliable ASW weapons such as an RBU-Hedgehog along with lightweight torpedoes and various sonar sensors would provide the Navy with a viable, effective, and expendable ASW vessel well suited for shallow water operations.

On a side note, a time-fused version could possibly be adapted to torpedo defense by launching a salvo timed to drop in front of an incoming torpedo and explode – the anti-torpedo equivalent of CIWS.

Note:  Russia offers the RPK-8 as an export weapon system – no development needed and it would be satisfying to “take” something from the Russians for a change!

Note:  This is not a replacement for anti-submarine torpedoes.  It is a complement intended to provide effective attacks in close range, surprise encounters.


(1)Russian Defense Export website, products/naval systems/shipborne weapons/RPK-8,


  1. I'm all for improved ASW capability, but a "surprise" encounter between a surface ship and a submarine is increasingly unlikely.

    Underwater sound propagation very much favors first detection by the submarine. Particularly a modern, small, quiet, non-nuclear boat. They exist in that medium and are much quieter than a DDG or an LCS.

    This is even more evident when one considers that our ships rely upon active sonar - which give away the ship's position.

    Put simply: a sub will likely hear a surface ship a lot further than the reverse. And either evade or engage well before the range at which a "hedgehog" could be employed.

    Now consider that an increasing number of subs are being fitted with anti-ship cruise missiles (ASCM) and the chance of a close-in encounter becomes even more remote.

    If anything - the money would be better spent on an extended range vertical launch ASROC. Keep the threat at a distance. IMHO.

    1. You need to research the sonar conditions in shallow water. Both sides are going to be wandering around almost blind. A sub is not going to be able to hear a surface ship any better than the reverse.

      The situation is made worse if neither side wants to use active sonar. They will literally stumble over each other.

      Victory in the shallow water region will go to the side that manages to figure out how to tactically utilize active sonar in an effective manner that does not result in getting targeted and sunk.

      I suspect we'll see a partial return to optical (periscope) detections out of a desire to avoid active sonar use. Of course, optical detections mean close range!

    2. I think you are the one who needs to do research​. Passive sonar detection inherently favor the submarine over the surface ship. Particularly in shallow water.

      And I think you will find few if any competent submariners who will use active sonar in wartime!

    3. I'll say it again. Shallow water ASW is a completely different beast. Research it and learn about it. There's a fair amount of information available with a bit of searching on the Internet.

    4. I too have toyed with this, especially for littoral class ships, which are kinda weak

  2. As far as I am aware, active sonar is not the primary mode of detection in ASW warfare, whether from the air or from the surface. Precisely for the reason you gave.
    Also, isn't it likely that the same acoustic conditions in the shallow water scenario described above will hamper the submarine's detection efforts?

    1. Due to the incredibly poor (noisy) sonar conditions in shallow water, passive sonar is ineffective. Active sonar will be required and is inherently short range. That range will be further shortened by bottom interference, false reflections from rocks, debris, sunken ships, etc. that clutter the shallow water bottom.

      Yes, the poor conditions and poor detection will work both ways. The submarine will have no better idea where the surface ship is then the reverse. I foresee both sides stumbling upon each other in many cases.

  3. Saab ASW-601 anti-submarine grenade launcher

    1. Yep, same idea although the Saab version apparently comes from a non-lethal starting point and it's unclear how lethal the newer version is.

    2. Wasnt there a bigger 375mm Bofors unit. the Swedes liked it for the shallow water reasons you have pointed out.
      ' It had two or four barrels and fired a 550-pound projectile up to 3,800 yards (3,500 m).'
      License if for US production. It may be a bit old but doubt it the business end needs changing much, ie dont make it 15km

  4. With the right modifications, they could also be very useful for short range shore bombardment and anti-small craft with air burst fuses and possibly simple guidance (inertial, GPS, or Laser).

    Randall Rapp

    1. Yes, the anti-small craft application could be effective although the firing rate is probably insufficient for a swarm attack.

      I don't think the explosiveness is sufficient for shore bombardment but maybe in an anti-personnel role? The range is probably not sufficient for shore bombardment. You'd need to be on the beach!

      Adding guidance kind of defeats one of the main attributes of the weapon which is cheapness. Everyone's first impulse nowadays is to make every weapon a do-everything one. We could add more range, multiple guidance mechanisms, enhanced sensors, networking, mid-course corrections, in-flight retargeting, and so on but we wouldn't be able to afford the final product, it'd be delivered years late, and it wouldn't be reliable due to its complexity. You get the idea, right?

      We already have weapons that can do all the complex stuff. We need simple, basic, reliable, cheap weapons that do one thing, do it well, and can be purchased in large quantities.

  5. I always thought that the western equivalent of the RBU-6000 was the Bofors 375 mm ASW mortar. Quite a nice weapon used by many NATO navies.

  6. While it would be nice to have something like this, a weapon like this needs deck space which seems to be at a premium on most of our ships.

    1. Go back and look at the number of weapons mounted on a WWII Fletcher class destroyer. We should have no problem finding room on any ship for a RBU-like weapon. Modern "stealth" shaping has robbed ships of horizontal deck space and I'm far from certain that it's a good idea.

  7. "We need an ASW vessel that is dedicated to ASW.."

    I agree. Build more VA Class Attack "ships" for this role...Subs are best at hunting subs followed by aircraft hunting subs. ASW destroyers are a WW2 type IMO and were not very effective, even during the Cold War when ASW got some attention (it doesn't today). IMO Surface ASW should be an collateral mission for the Burkes, not the reason why we build more.

    Maybe a new frigate with robust ASW would should be you surface ASW ship...

    From your post I am more focused on the ASW platform vice the individual weapons because getting close to a submarine that has all the advantages, particularly the time factor, that having all the hedgehog type weapons loaded aboard a blind surface ship of any variety will make no difference, the sub has the odds going for it.. even with simple torpedoes.


    1. I agree that a sub is the best sub hunter. However, in an actual war, our subs will be very busy conducting open ocean ASW, ASuW, cruise missile strike, intel and surveillance, etc. The reality is that there will be times and places where just won't have any subs available for ASW but will still have need to sail warships, merchantmen, and convoys through submarine waters. We WILL need ASW ships especially around the lower intensity combat areas.

      Further, the US has only large nuclear attack subs and, by all accounts, those are not optimum for shallow water work. It may be that shallow water ASW is better left to cheap, expendable, dedicated ASW ships.

      Lastly, to repeat, the US has only large, EXPENSIVE, nuclear attack subs ($2.5B each). Pitting those against $200M-$500M non-nuclear subs is playing on the wrong side of the cost curve. Again, a $500M expendable, dedicated ASW ship may be preferred in some situations.

    2. Perhaps the navy should acquire some AIP diesel subs.

  8. I was thinking about lower intensity combat areas.

    In a war between China and the US, the Chinese could try to forbid the arrival of US ships to the theater.

    Perhaps, they could try to intercept US Navy ships not only off San Diego, Hawaii and Guam, but also avoiding that Atlantic Fleet ships reinforce the Pacific Fleet ships.

    With that goal, they could try using diesel-electric submarines for closing the Panama channel, the Magellan Strait and Cape Horn, the Suez channel and the Cape of Good Hope.

    Those submarines could be supported by the huge Chinese fishing fleet, which has an impressive array of logistic ships.

    All of said choke points would eventually be lower intensity combat areas.

    With less than 125 P-8 Poseidon MPA, the US Navy would have a difficult task performing ASW mission in all of this areas.

    In such, places a second tier ASW ship could be the only available ASW asset.

  9. No ship with hundreds of sailors aboard is expendable, regardless. The expense of the SSNs is worth it. As you know ASW is a team sport and we've gotten real slack at training. There is no magic bullet to fix it and ASW from the CVN since the premature retirement of the Viking just exacerbates the issues. IMO adding a new surface platform won't answer. The only counter is more SSNs and P-8s until we get or collective heads out of you know where!

    1. Expendable in the sense that they are cheap enough to actually use them at the task for which they are built.

      Will we actually risk a Ford class carrier, at $15B+, in combat? I doubt it. It's not expendable.

      If a ship, aircraft, or ground unit is not expendable, it's of no use or value. The cold reality is that individual soldiers and sailors are expendable in the sense that we are willing to risk their lives to accomplish an appropriate mission.

      Everything and everyone in the military should be expendable otherwise they're useless. Now, I assume you understand that I'm not advocating human wave attacks because I place no value on life. Instead, I'm advocating what the US military has always done which is to risk ships, aircraft, and lives in the pursuit of suitably worthwhile missions.

      To your main point, yes, ASW is a team sport and the more players, the better. Thus, a small, dedicated ASW vessel IS a good idea. No, it's not the ultimate, only answer but, to be fair, I never claimed it was.

  10. RE.a sub is the best sub hunter.
    As CNO says Navy is on the wrong side of the cost curve. The two 2017 SSN Virginias costing $2.7 billion each and when Block V comes on stream with the VPM will be looking at $3+ billion.

    SSKs cost less, may buy three to five for price of a single Virginia. A CNAS report table p.9 showing by 2030 Chinese will have 4 SSNs and 75 SSKs versus US 42 SSNs and 0 SSKs. I'm sure the Chinese SSKs will be very capable boats with the latest tech and cost less and be able to out build US by ratio of 10 to 1 or more as Navy insists on SSNs and so limited build capacity with only two nuclear capable shipyards and has similar problems in maintenance, USS Albany, plan two years, actual four years and USS Boise last deployment ended Jan. 2015, expected return to fleet 2020 or later.

    Options as a result of the massive R&D into LIBs, lithium-ion batteries by car industry and others.

    The eleventh large SSK Soryu, first Mk 2, 4,200 tons, with improved underwater endurance by using LIBs, ¥64.3 billion/ $583 million, 2015 Japanese Defense Budget.

    The Italians have just ordered four new gen. U212s,1,800 tons, powered by LIBs, previous four Italian U212s used the specialized AIP Siemens PEM, proton exchange membrane, compressed hydrogen fuel cells, so Italians changed to LIBs in preference to PEM AIP for the better underwater endurance.

    South Korea is looking to use Samsung LIBs for the three new 3,000 ton Jangbogo III Mk2

    On the horizon is the possibly the better lithium sulfur battery (LSB) 2020+ for SSKs.

  11. I see your point CNOPs and I appreciate the debate but NAVSea will add on if they built a new DD from scratch. Same for the excellent idea for diesel AIP subs. Bird in hand logic for me until we get serious blue water Navy proponents up and in position to make a serious attempt. I hold my breath on that happening....

    1. Would the Navy take any reasonable proposal and gold-plate-distort it all out of recognition and drive the cost up by a factor of a zillion? Of course they would! So, you're right.

      However, this blog is partly about describing things as they are but also partly about describing things as they ought to be. If we only stick to as-they-are and no one ever describes a better way, nothing will ever change. So, part of my goal is to describe the current reality but the other part is to describe the better way. A small, dedicated, expendable ASW vessel is a better way. The fact that the Navy is probably incapable of building such a focused, simple ship is irrelevant in a discussion of the way things ought to be!

      One cannot be a visionary if one sticks only to the current situation. If Robert Fulton had stuck to the as-things-are, our aircraft carriers would be sail powered and EMALS would be a system of pulleys and ropes being yanked by sailors.

  12. Rocket powered, detonating on contact with hundreds of rounds carried potentially, all on a cheap small hull?

    Shore bombardment anyone? Properly designed, I think a corvette in the 2000 ton or smaller range (is a ww2 destroyer sized) combatant could fill a lot of capability gaps while being cheap enough to mass produce.

    1. "Rocket powered, detonating on contact with hundreds of rounds carried potentially, all on a cheap small hull?

      Shore bombardment anyone?"

      Are you familiar with the LSM(R) vessels of WWII? We already figured all this out many decades ago and it's frankly embarrassing that the Navy has forgotten and we have to relearn it and debate it.

      Your comment is just as appropriate today as it would have been in WWII.

      If you haven't seen it, check out the post on the LSM(R), here

    2. Sorry for the late hit but I’d point out that we wouldn’t have to buy RBU-600 (or steal design) from Russians. The Indians make their own version they’d be happy to sell. From what I read on Maxdefense blog, the Indians were willing to The Philippines two Kamorta-class ASWs frigate with sensors and weapons (but ex ammunition) for $160M each. Filipinos ended up going, for political reasons, with South Korean Incheon-class for slightly more. Congress would never go for buying foreign-built ships but the the US Navy could do worse than buying as many Kamortas and Incheons (and Taiwan’s $75M Tuo River corvette) as the their yards can produce.


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