Friday, June 24, 2016

Torpedo Defense

Many people believe that torpedoes are the biggest threat to surface ships due to their combination of stealth delivery, large warheads, subsurface detonation effects, and the virtual absence of any effective defense.  Tough to argue with that although mines are equally devastating and ballistic missiles, if they hit, would be potent.

So, if torpedoes are such a threat, we must have put a great deal of research and development into anti-torpedo defense (ATD) over the years and we must, by now, have some pretty robust defensive measures in place, right?  Look at the massive effort that has gone into AAW/SAM efforts against cruise and ballistic missiles.  Surely, we must have been equally active and successful in our ATD efforts.  Well, let’s look at the Navy’s current state of the art in ATD.

There are two broad categories of defense, hard kill and soft kill.

Hard Kill

In the early 2000’s, the Navy attempted to develop a hard kill system which used a small, agile torpedo to intercept and kill an incoming torpedo.  From the Navy website comes this description of the Anti-Torpedo Torpedo (ATT) system (1).

“The Navy and Penn State University’s Applied Research Laboratory are also developing an Anti-Torpedo Torpedo (ATT) that could be launched from both submarines and surface ships to intercept and destroy inbound threats. … As currently configured, the 200-pound ATT is 6.75 inches in diameter, 105 inches long, and powered by a stored chemical-energy propulsion system similar to the Navy’s MK 50 torpedo. Advances in electronics miniaturization, significant increases in microprocessor computation rates, and sophisticated processing algorithms have overcome the shortcomings of the previous ATT program, which was cancelled in 1994. A capability to launch multiple ATTs simultaneously to defeat multiple, salvo-fired torpedoes is a required feature. Tests of the ATT have been planned for late 2006.”

The ATT system has apparently now morphed into the Surface Ship Torpedo Defense (SSTD) system with tests having been conducted in June of 2013.  The basic components remain unchanged and include the Nixie towed decoy and detection system, now called the Torpedo Warning System (TWS), and the anti-torpedo torpedo now being called a Counter Anti-Torpedo (CAT).  Additional testing is planned and initial operational capability is planned for 2019 with full fleet-wide adoption by 2035.  According to DOT&E, testing has, thus far, been conducted under fairly benign and unrealistic conditions (2).  Exercises were conducted at much deeper depths than the expected threat torpedoes would operate and the TWS and CAT were not, therefore, tested at the expected operational depth which would include significant surface water effects.

The CAT is an all-up round housed in a canister and ready for launch.  The round is designed for high speed and maneuverability and uses a stored chemical energy propulsion system.  The CAT safety/arming system has, apparently, encountered an unspecified major anomaly that the Navy is still working to overcome.

The overall system was, at one point, designated WSQ-11 (circa 2004) and was tested on USS Cleveland, LPD-7, in Apr 2006. 

Note that the development path has been convoluted and has intermixed with UK efforts, as well.  Some of the designations and incarnations are debatable but, for our purposes, the basic technology is correct.

Soft Kill

Nixie.  The Nixie SLQ-25 torpedo decoy is a towed device that emits acoustic signals intended to decoy and pre-maturely detonate torpedoes.  The device has been in use for decades and more recent versions incorporate add-on torpedo detection sensing devices and enhanced signal generators.  The latest version incorporates active sonar sensing.  Defense Industry Daily website reported a 2005 contract for 3 SLQ-25 sets for around $7M each.  A more recent order for 5 SLQ-25C systems was placed for a little over $1M each.  It is not clear whether that was for complete systems or just the decoy emitter, itself.

Of course, the Russian Type 53-65 torpedoes are wake homing and are not susceptible to acoustic decoys like Nixie.  Further, wire guided torpedoes are far less susceptible to decoys as the base submarine is able to use its more extensive and capable targeting capability.

A roughly equivalent system apparently exists in the Royal Navy as S2170 and is also known as Sea Sentor.

Submarine Decoys and Noisemakers.  Submarines employ various acoustic decoys such as Ultra Electronics Mk 2/3/4 Acoustic Device Countermeasures (ADC) which is a 3” or 6.25” diameter expendable acoustic decoy.

The old Mk 57 Mobile Submarine Simulator (MOSS) was a 10 inch diameter, mobile decoy that was launched from a torpedo tube.  MOSS has since been replaced by the six inch EX-10 Mobile Multi-function Device (MMD), which can be fired from a countermeasures tube.

LCS Multi Function Towed Array (MFTA).  The SQR-20 (now TB-37U) MFTA is a long 3″ diameter towed array for surface ships.  It has both active and passive sonar capabilities and is claimed to have improved better coverage, detection capability, and reliability than the SQR-19 TACTAS and includes a torpedo detection capability.  This is not actually an anti-torpedo system since it is not currently coupled to any defense mechanism.  It is a detection system, only.

A May 2015 contract for seven MFTAs was issued at around $4M per system.

A Light Weight Tow (LWT) Torpedo Decoy for LCS functions similar to a Nixie.  There have been claims that it is effective against wake-homing torpedoes although I have been unable to authoritatively confirm this and the mechanism for such a capability escapes me.

So there you have it.  That’s about the state of the art in ATD.  Not very impressive for all the years that we’ve had to work on it and the enormous destructive potential of the torpedo threat.  As with mines, the Navy seems to have largely ignored the threat in favor of building shiny new ships.

So, what could be done in the way of future ATD?  Here’s some ideas, unbounded by physics or reality.  Honestly, the liquid phase (water) physics are poorly understood by most of us so some of these ideas may be completely unfeasible.  Still, they’re worth a bit of thought!

  • Enhanced Decoys – mobile decoys already exist and are used by submarines.  There’s no reason why mobile decoys couldn’t be adapted to surface ships.  They would be launched from ejector ports just above, or under, the surface.

  • Torpedo Belts/Bulges – These were effective in WWII and can be today.  Today’s threat is the under-the-keel explosion but there is no reason why the belt/bulge can’t be extended around the keel.  Similarly, collapsible voids and shock absorbing plates would seem viable.  There is much that naval engineers can learn from land vehicles about absorbing shock energies.  Vehicle designers have learned how to absorb and redirect the explosive energy from IEDs and mines from beneath the vehicle.  There’s no reason similar technologies couldn’t be applied to ships.  Remember, while it would be nice if a torpedo belt or similar structure could completely shrug off a torpedo’s effect, that’s not really the goal.  The goal of such armor and structure is to mitigate the effects of a torpedo explosion.
Torpedo Belt / Bulge

  • Anti-Torpedo ASROC / SAM – Borrowing from the old ASROC concept, how about launching a rocket borne anti-torpedo torpedo to an intercept point far from the ship.  The distance would allow multiple intercept attempts just like the SAM AAW concept.

  • Super Cavitation Darts – Super cavitation allows torpedoes to achieve very high speeds of 100-200 kts.  Why not apply the principle to small “darts” that contain only a sensor head and explosive warhead?  The ship’s launch mechanism would impart all the speed necessary for intercept and the dart would have no need for an engine or fuel.  This would be a great application for a very small rail gun.  In any event, the darts would be launched at an intercept point and the dart’s small sensor/fuze would detonate the warhead if the torpedo were detected.  The main question would be what range could be achieved before the dart slowed to a stop.
Super Cavitating Dart

  • CIWS/RBU – The RBU is the old Soviet anti-submarine rocket launcher.  It’s somewhat analogous to the old US Hedgehog system.  If that were combined with a CIWS type system, it could launch a “wall” of exploding rockets on or just in front of the torpedo.  The CIWS aspect would guide the fall of rockets to meet the torpedo just as it guides the shells to meet the target aircraft or missile.  The system would depend on sheer volume of exploding rockets to destroy the incoming torpedo.
RBU ASW Rocket Launcher

As I said, some of these ideas will probably not be viable but they're worthwhile starting points for development of new anti-torpedo technologies.

Given the seriousness of the threat, the Navy needs to be equally serious about countermeasures.  It's baffling that ATD has been ignored the way it has.  We need to quit obsessing over new ships and start protecting the ones we have.


(2)DOT&E, 2013 Annual Report


  1. Ships keels would need to be massively reinforced to survive a keel explosion. Direct blast damage is not the critical factor, it is the point loading by the blast void that breaks the keel. The entire weight of the ship ends up being supported by a small area instead of being distributed by the entire length of the hull.

    1. Mat, land vehicle engineers have learned how to redirect and distribute the forces from a mine exploding under the vehicle. There's no reason that naval engineers can't do the same. Massively reinforcing the keel is not the only, or even the preferred, way to approach the problem.

      Multiple collapsible voids, spring backed plates, layered armor, slanted hull bottoms (similar to a vehicle's "V"-shaped bottom), and flexible structures that pass on the shock rather than focus it are just a few possible approaches that I can think of and I'm not a naval engineer. The Navy has quite laggard in its development of ship protection.

    2. Under keel explosions effects are different for a 3000t Frigate and a 100,000t carrier. Obviously the worst result is from exactly midship, but how often could that be.
      The bulges both internal and external relied on water -air-water compartments to limit shrapnel and spread the shock. They would still be used today for all carrier type designs.
      The hedgehog was a UK developed weapon.

    3. "The hedgehog was a UK developed weapon."

      I stand corrected! Thanks.

    4. Mat seems right that the destructive effect of an under-keel explosion is not mostly due to its blast, but rather to the loading imposed on the ship when it finds part of its thousands, or tens of thousands of tons temporarily suspended over a large gas bubble. That is not the case for a land vehicle, in which the hull always has gas beneath it. Therefore, all the intelligent measures for protection of land vehicles (slanted bottoms, spring-backed plates, and so on) that CNOps suggests could be applied to ships do rather seem to be beside the point.

      Or am I wrong? I'm not a naval engineer either.

    5. Well, ships are built in air and enter drydock, admittedly with support, but to believe that a bubble alone means instant death to a ship seems a bit extreme. In extreme weather, smaller ships sometimes find their keels exposed momentarily and don't instantly fold in half. As you say, though, I'm not a naval engineer, either so who knows?

      Consider, further, all the things we build that are exposed to far more stress than a ship's keel: skyscrapers whose base must flex and support the fulcrum of the entire building, bridges that must expand/contract and flex and extend over miles, and so on. I'm saying that the lessons from the land can be applied to ships. The Navy has been remiss in investigating how to adapt those technologies.

    6. With much due respect and humility to ComNavOps (btw, first time caller, long time listener), I must agree with Mat.

      Ships seem to face a much different problem from the void created by a torpedo. In this case, the physics may be more analogous to a building than a land vehicle. The effects of a MK48 from the test videos I've seen remind me of a sink hole opening under a building; albiet at a very rapid pace.

      If 50% of the land under the middle o of a building suddenly disappeared, it is reasonable to expect it to collapse in upon itself. I believe these are the effects we see from torpedoes like the MK48 designed to create a void under surface ships.

      The solution, from my sophomoric point of view, seems two fold. The first, unsuspectedly, might be to make the ship as light as possible. The less weight the load bearing members carry in such a situation, the less prone the will be failure.

      The second would seem to be to spread out the ships load. In this instance, something like a trimaran (and I'm ***NOT*** mentioning it because of the LCS) may have an advantage; particularly, if the weight load is highly distributed.

      Of course good luck torpedoing a Pegasus class, at least when she's up. ;)

    7. Anon, welcome! Don't hesitate to jump in and comment. None of us really know the physics involved in this so we're all just speculating. You may well be right!

    8. I note that this problem is not unique: the original "torpedoes" (mines) also inflict similar damage.

      From an engineering perspective: size matters larger ships are less vulnerable.


    9. Actually, I do know the physics involved in torpedo detonation. The only way to dissipate the force is through a combination of liquid and air loaded voids, with a torpedo bulkhead inboard to catch the resulting shrapnel. A good system against a 700lb TNT equivalent required four to five layers and a combined depth of 22 to 25 feet. As modern torpedoes carry much larger charges than this, a Side Protection System becomes volume/beam prohibitive, and was never possible along the bottom of the hull due to stability issues. Garzke and Dulin's Battleship series covers this pretty well, and Friedman's Battleship Design and Development goes into the math concerning metacentric height issues. Both the X-craft damage to the Tirpitz and the mine damage to HMS Belfast are instructive as the whipping, which is a ship-wide event.

    10. "The only way to dissipate the force ..."

      You're describing the way torpedo armor was done and, to a very large extent, still is done. That's limited thinking by the naval engineers. I'm talking about adapting other shock absorbing technologies to naval use.

      I've already listed several candidate technologies. Consider some more like reactive armor or composite (Chobham) armors rather than simple steel plates.

      Thinking even further outside the box, consider the example of a plane landing on a carrier and the arresting gear that stops the plane. All the force of the aircraft's momentum is captured and transferred to various shock absorbing mechanisms so that both the plane and arresting wire survive the landing. Perhaps there is a way to capture and transfer a torpedo's shock. The point is not to jump on any single suggestion but to consider a broad range of possible adaptations that might be helpful. It's unlikely that there is one, single solution. An effective belt/bulge solution will likely incorporate several approaches working together. To the best of my knowledge, naval engineers have not yet considered any of the "land" solutions. That's the point - to think beyond the conventional.

    11. The problem is that the path into the ship is the one of least resistance. With reactive armor the force is being redirected into a compressible medium; air. Water is not compressible and so the void of the internal volume of the ship is where the force gets directed. Venting poppets were tried in several capital ship SPS systems, but the expanding wave moves so quickly into the ship that these systems failed and still added to loss of waterplane. The problem of whipping also makes dissipating the energy through the ship's structure problematic. The point of failure then becomes the ship's highest continuous deck (i.e. the upper past of the ship's girder), not to mention dislocation of machinery and any systems high in the ship like radar and communications antennas. Unless you can figure out a way to make the surrounding ocean the path of least resistance then one Mk 48 ADCAP is a ship-killer even if the ship doesn't sink. Is is useful to keep in mind that an underwater explosion is a series of events (pressure wave, then bubble collapse, then explosive wave, then collapse, plus shrapnel) and in shallow water this gets even worse.

    12. Well, explosive reactive armour on a ship has several problems. The hot gas from ERA detonated in air can expand quite freely. In water, it adds to the gas bubble that does the damage. ERA on a tank can also be dismounted when combat isn't expected. On a ship, that needs a dry dock, and sailing around with a hull covered with explosives may present a safety problem. Also, ERA is good against long rod penetrators and shaped charges, neither of which is a normal torpedo warhead.

      Again, composite armour is specific to shaped charges.

      A torpedo bulge was a way of retrofitting a side protective system onto a ship originally built without one. They're more effective when they're designed into the ship to start with, but they take up huge amounts of hull volume, especially if you build them around the bottom of the vessel. With modern explosives in torpedo warheads, they aren't practical on destroyer-sized ships.

      There may be an effective way of reducing the effects of torpedoes, but I don't think any of these ways are practical.

    13. CNO, the physics between land and sea based vehicles are completely different. Land based vehicles inhabit a highly compressible medium: air. That means that adding a little steel (much less compressible) and a little shaping can redirect a blase.

      Sea Vehicles live in an incomprehensible medium: water. That means that even with near infinite armor, the ship will still compress more than the surrounding environment.

      An under keel explosion wrecks ships because very rapidly you have a highly compressing event (the initial shockwave) followed immediately by a void/vacuum event. This ship simple cannot handle the massive amount of dynamic force this causes on the keel.

      While it might be possible to design a ship that could withstand it, what you would be left with would more resemble a steel anchor than an actual ship. Think 30k ton displacement corvettes with crew room for 2, a max speed of 1 knot, and max endurance of 100nm. AKA, the very things that are required on a ship (void volume, buoyancy, etc) are the things that make a keel explosion so destructive.

      What you are asking is similar to: how do you defend against a 1 GT nuclear weapon? Answer, you make sure it doesn't go off anywhere that is anything like possibly close to you.

    14. Wow! I explicitly said that the point was not to jump on any single idea but to consider a wide range of unconventional ideas that could be adapted from land applications and yet you all jumped on a single idea. I'm neither an naval engineer nor an underwater explosives damage effects expert and neither are any of you, I'm pretty sure. You're all taking some basic concepts and claiming that nothing can work. That is exactly the kind of limited thinking that wrote about. Once upon a time we thought (fill in the blank) was impossible until we figured out how to do it. This is the same situation.

      You can reply with very limited understanding about the impossibility of providing torpedo protection or you can accept the simple statement that we need to expand our range of thinking about possible solutions. I've made no claim that any of these possibilities will work. I've simply stated that the Navy is long overdue to start thinking outside the conventional box.

      I'm disappointed at the reaction.

      Finally, remember that torpedo defense is not an all-or-nothing proposition. Just because a given protection scheme won't provide 100% protection doesn't mean it has no value. I've discussed this repeatedly. The value of armor is the ability to mitigate the effects of the weapon. That remains true with torpedoes. Rather than sink in two minutes after a hit, maybe we can reduce the damage to a hole that our damage control can deal with. That's a win in that scenario.

      I have the impression that you people would be making the same comments to the Wright brothers on their blog, telling them that it's not possible to fly!

    15. What I'm saying is that an inherent system like SPS will not work without prohibitive costs to things like usable ship volume and stability. You have to kill the torpedo before it gets there.

  2. Interesting thoughts...

    An area you somewhat overlooked is the torpedo detection aspect. For a surface ship, detecting and localizing an incoming torpedo is a hard problem, and that problem needs to be solved in order to be effective in many of the solutions that were proposed. Note that I said localizing, since a bearing-only detection does you little good for some of the concepts being proposed.

    I always wondered if you could just detonate a large charge in your wake to help defeat the wake-homer...even if the incoming torpedo is not damaged, you put so much noise in the water and help "break" you own wake that it may make the weapon ineffective in combination with ship maneuvers.

    1. You're quite right. As with AAW, targeting must occur before any defense can work. I have limited space in a blog and I knowingly shorted the detection aspect in favor of the defense aspect. Quite right of you to note it!

      Unfortunately, I know little about the details of wake homing torpedoes so I have a hard time even speculating about countermeasures.

  3. Supercavitation works by generating a gas bubble around the torpedo (or in this case the dart) which reduces drag by minimizing water. As described, the Super Cavitating Darts would also need a gas generator to create the bubble around the dart.

    The Russian Shkval uses inertial guidance and I think these darts would too. I can see these darts following a pre-programmed trajectory and detonate at the predicted intercept point. Maybe in practice, you launch several or more to cover a larger area and ensure a kill.

    1. Also, bear in mind that these darts would be very short range compared to a 20-50 mile range torpedo. The darts would be analogous to a close in weapon system. I would think a half mile or so would be about right, maybe less? Thus, the gas generation would only need a very small capacity.

      At that close range, guidance would not be necessary. It would be a simple calculated intercept point.

      As you suggest, several darts, covering the predicted intercept point, would be desirable.

    2. Keeping with the CIWS analogy, I bet those 20mm rounds from a Phalanx, properly aimed, could hit a torpedo. The minimum elevation on the Block 1 is -20° and -25° for Block 1B. If a Phalanx round travelled 40 meters (before slowing down too much) after hitting the water at -20°, it would reach a depth of 13.7 meters. The depth is 16.9 meters at -25°. Just a thought.

    3. Walter, I suggest you read up on the effects of bullets entering water. You aren't going to get 40ft let alone 40m with a bullet fired into water at anything approaching normal bullet speeds.

      Two example videos:

    4. I stand corrected. It's probably a few meters at best.

    5. Mythbusters TV show (for those who are familiar with the show) did a segment of diving underwater to escape bullets and found that guns ranging from 9mm to 0.50 cal penetrated only a few to several feet deep (fired at a 25-30 deg angle to the water. However, the big caveat is that the main mechanism of slowing of the bullets was shattering of the bullets on impact with the water. Well, of course that would slow the bullet! So, that still leaves the question of what something much denser, like a CIWS depleted uranium round or tungsten round would do. If the round held together, how far would it penetrate the water? I have no idea. Also, the CIWS has a much higher muzzle velocity (3600 fps) than even the 0.50 cal rifle (2700 fps) that was tested so, again, greater penetration.

    6. "At that close range, guidance would not be necessary. It would be a simple calculated intercept point."

      Of course, this assumes that the ship making the engagement has a good lock on the target in order to calculate an intercept point.

      "So, that still leaves the question of what something much denser, like a CIWS depleted uranium round or tungsten round would do."

      There are already programs out there with bullet rounds designed to penetrate water. A couple of links to the now cancelled RAMICS program are below.

    7. RAMICS - great reminder. I had forgotten about that one! So, the water penetration distance is probably achievable.

  4. I think there are a few reasons

    First and foremost, when compared with missiles, torpedo are very slow and very short ranged.
    A high altitude launch of a missile could be 300 miles away and be based on visual information, and a missile could close that gap in 8 minutes. Unlikely, but possible.
    100 miles and 3 minutes is well within capabilities.

    A max range shot for a topedo is 30 miles, and would entail a 20 minute swim time.
    Realistic shots are ranged at a couple of miles, and even then, would be essentially unguided for much of the trip.

    Shooting the shooter is by far the most viable strategy, followed by simply outrunning the Torpedo, which is maybe twice as fast as a ship, or dodging it / decoying it.

    Wake homing Topedo sound great, but a Torpedo with a speed of 60mph, and a range of 30miles, chasing a ship moving at 30mph, has a VERY small kill box to fire from.

    I hear a lot about super cavitation as a means of propulsion, but I'm yet to see it actually function, or anyone even explain it.
    The whole reason propellors are able to cavitate is because they dont move through the water, I'm yet to grasp how the bubble of air surrounding the torpedo will be magically propelled through the water.

    1. Supercavitation isn't a means of propulsion at all. The basic idea is that your weapon has a blunt "mushroom" nose and a smaller diameter body behind it. The sudden drop of pressure as water flows past the edge of the mushroom drops the water below its vapour pressure and some of it turns into gas. That gas imposes much less friction on the skin of the weapon than water flowing over it at high speed would. If you design it right, the overall drag is less at high speed, even though the mushroom nose has quite high drag.

      However, the problem is sustaining speed. The Russian Shkval torpedo is rocket-propelled, and the gas from the rocket exhaust helps maintain the gas bubble. I don't know how far a supercavitating projectile fired from some kind of gun could sustain enough speed, but I doubt it's very far.

    2. "The sudden drop of pressure as water flows past the edge of the mushroom drops the water below its vapour pressure and some of it turns into gas."

      And thats where the problem lies, creating that pressure drop isnt free, theres a phenomenal energy cost involved.

      It seems a pretty simple case of increased speed at the cost of range, which isnt bad, but some people think we're going to get Torpedo with 200 miles ranges and 500mph speeds.

    3. "... Torpedo with 200 miles ranges and 500mph speeds."

      Well, that's about as realistic as the people who think the B-2 has magnetogravitic propulsion and is hypersonic. The Shkval seems to have been developed on one of those Soviet "invent this, don't stop until it works" projects and makes about 200 knots for less than 10 miles. Drastic improvements in performance seem unlikely, and overcoming the problems that it's hugely noisy and can't use acoustic sensors likely impossible.

  5. The USN's actual torpedo defence strategy seems to be to focus of the carrier battle group, and assume that the escorting SSNs will detect and kill enemy submarines before they get shots at the surface vessels.

    1. Agree.

      The "escort" SSN is is the USN strategy, but it is a misuse of assets to tie attack submarines to surface forces.

      The aviation analogy is to rigidly assign fighter squadrons to escorting bombers instead of allowing them to perform sweeps in the general geographic area and operate at speed/altitude profiles favorable to fighter (not bomber) operations.

      The most effective ASW campaigns have prioritized destruction of enemy logistics, repair, and C4ISR networks.


    2. The "War Load" of the QE class is expected to be 36 strike F35s and 9 medium weight ASW helicopters.

      Plus the escorting ASW figates and SSNs.

      "The "escort" SSN is is the USN strategy, but it is a misuse of assets to tie attack submarines to surface forces."
      I hope that the "escort" SSN is an "assigned" SSN, rather than an actual asset under day to day control of the carrier, which would be a disaster.

    3. Since the escorting SSN or SSNs have no way to communicate with the carrier without compromising their own stealth, at least a bit, they are not under direct control. It seems they are normally some way ahead, looking for opposition.

      The drawback is that they have to be told where the carrier is going to sail, and if that is changed in a hurry, then it's easy for them to be out of position and need a while to get back ahead of the carrier.

      This organisational structure seems to be due to an interesting piece of behaviour that the USN displays. The different communities (surface, aviation, submarine, etc.) are rivals for budget. Changing the fleet organisation requires compromise amongst them. Escort SSNs may not be the best way to defend against enemy submarines, but it was the strategy that required more boats for the submarine branch, which motivated them to sign up for it.

  6. Haven't there been plenty of WWII ships, especially the Battleship types, that have survived quite a few torpedo hits? There was even the atomic underwater explosion Baker test in Operation Crossroads, and some of the Battleships there seemed to survive better than expected.

    1. Depends on the Torpedo
      Air launched light weight torpedo are "survivable", but their job is to "mission kill" ships really, no one expects a harpoon to sink a ship, although they could.
      Sub launched heavy weight torpedo are a lot harder to survive, its not a great sample, but the only two ships hit since the second world war, a 1950s small ASW frigate was lost with all hands following a single hit, possibly one survivor, a 1930s light cruiser was hit twice and went down in less than 20 minutes.

      Torpedo bulges and the like can help, in theory, I think Torpedo could be designed to beat them.
      Current Torpedo are fairly "dumb" in their blast effects, they are just big bombs, they smash the hull and create a void underneath to snap the ships, spine, if you will.

      Masses of reinforcement and compartmentalisation could defeat that, but what do you do about a shaped charge torpedo?
      An anti tank missile is designed to explosively drill a small hole in the hull of the tank and then kill the crew, a shaped Torpedo could easily drill a hole through a ships hull, dozens of water tight compartments and the ship goes down anyway. That same hole above the water line is irrelevant, underneath its a very quick death.

      Most famous actions have been light air launched torpedo either actually destroying propulsion or steering gear, or causing so much flooding that the ship was slowed and significantly harder to control.

      I'm not actually aware of any second world war battles in which submarines attacked battleships?

    2. "Haven't there been plenty of WWII ships, especially the Battleship types, that have survived quite a few torpedo hits?"

      Yes, even up to the terrifying 'Long Lance' torpedo (or, more correctly, it's submarine launched cousin, in the case of the USS North Carolina).

      That being said, in the 80s the Navy studied the capabilities of the Iowa-class Battleship against then-modern torpedoes (which are still in use by the US Navy).
      While they determined that only a seemingly low number of hits (5) would be required to sink an Iowa, the circumstances for those hits to happen one right after the other was essentially zero.
      As a matter of fact, they ended up concluding that the Iowa was 'effectively immune' to Mk48 ADCAP torpedoes.

      So, yes, Battleship-style TDS (Torpedo Defense System/s) still do work wonders against even modern keel-breaking torpedoes, in concept at least.
      The Iowa was saved based on her almost excessive (for the time she was built) length (although her length is not that much today).

      - Ray D.

  7. Heres a good study looking at how modern ships are affected by torpedo hits ( or similar like that on USS Cole). Also included is ROK covette sunk by North Korean torpedo.

    1. The author completely misses the mark on his initial description of the Cole damage. His complete lack of understanding of this damage calls into question the rest of the article. I seriously doubt that the author has any expertise in naval engineering or explosives damage effects in water.

      FYI, the Cole damage effects were a function of the strake thickness. Photos clearly show the explosive sheer along the line of the thicker, upper strake. It had nothing to do with water effects.

      For more information, see, Ship Construction and Naval Armor

    2. The article I linked too refers to the difference in damage below and immediately above the water line and gives reasons. What you have described :"horizontal weld line that runs the length of the hull about halfway between the rail and the water." is a separate issue and quite valid of course.
      Combining the information we can see 3 damage zones. below water, above water and above strake line.
      Thanks for the extra info.

  8. As discussed, the use of Hy-80 steel in USS Cole helped limit damage. This old research paper (1986) in Journal of Ship production showed that HY-80 usage had increased up till that time
    "The use of HY steels has increased markedly in the past
    ten years and is continuing to do so today. For example, in
    a typical cruiser hull form, historically about 707 tons of
    HY-80 was used. Today, the use of HY-80 (or equivalent
    HSLA-80) is in the range of 1300 tons, done in order to reduce
    displacement by replacement of the lower-strength HTS.."
    The cruisers of the time would have been Tico's. Another reason to build them as specialist vessels and not rely on DDGs. of course the use of HY-80 ( first used in the hull of the revolutionary Albacore sub) leads to a large increase in welding costs.

  9. Under keel void detonation does require some fairly precise calculations.

    Dependant on the size, heading and speed of the ship the torpedo must position itself fairly accurately directly in the middle of the ship at a set depth beneath the keel then detonate.

    This is partly why speed and manoeuvring is a good defence if you can be made aware of the incoming torpedo early enough.

    I would imagine Nixie and the like effectively mess with the torpedoes idea of where the middle of the ship IS.

    And I think this would be a good way to go. These torpedoes will only detonate when the exact parameters for keel detonation are met, and the path they have to take to position themselves is complex. You may be able to force them to run themselves out or prematurely detonate.

    On the active defence side. I’m quite likening your hedgehog idea.

    Hedgehog was a forward firing multi launch depth charge device, that instead of using large barrel charges. Used a pattern of small depth bombs ( akin to mortar rounds ) thrown several hundred feet out ahead of the ship.

    These bombs fell into the sea and sank into what you might call a cube pattern. When the “cube” detonated the bombs shockwave fronts were designed to add together such that a submarine within that cube would effectively be crushed ( one of our better inventions I always think  )

    Perhaps this could be deployed from a turreted high rate of fire launcher. The charge of each bomb needn’t be large, it’s the timing and the positioning that is crucial. And obviously hedgehog gets round the need to be accurate and physically hit the incoming torp as anything within the box gets suddenly and irrevocably smaller followed quite quickly by bigger but bittier.


    1. There are lots of unexplored ideas. I like the cruise missile torpedo, that (like a torpedo bomber) glides in, IDs the target, and releases a homing torpedo a mile away.

      Or a shotgun torpedo. At a few hundred yards it fires off a dozen fast rocket power mini torpedoes each the size of a baseball bat. (look at a hyrda rocket pod with 70mm rockets) This spread covers a wide area each punches a hole as its incendiary warhead ignites. So countermeasures don't work and a ship is left with fires and several small holes below the water line in different compartments.

      Also, the harbor torpedo, described here:

    2. Well we were talking torpedo defence really.

      For those of you that haven't seen it. This is the Russians current offering. They claim to be deploying this on their current newest corvettes and a few other platforms.