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
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
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.
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| 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.
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| 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.
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| 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.
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(2)DOT&E, 2013 Annual Report
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