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.
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




