Why aren't there anti-torpedo torpedos?

I like a good techno-thriller and i picked up a copy of Tom Clancys ‘SSN’ second-hand the other day. As the name suggests it involves submarine warfare and it started me wondering.

How come ships don’t have anti-torpedo torpedos?

After all anti-missile missiles are an integral part of any modern warship design, so why not torpedos?

If anything i would have thought they’d be easier to make than there airborne equivalents. A torpedo moves at a tenth the speed of a missile at best and i can’t see that a defensive torpedo would have much trouble hearing (and so homing in on) a large anti-ship weapon thundering through the water.

So anyone know why? Is there some technical reason i haven’t spotted that makes them unfeasible.

I’ve read parts of that book too, and it’s a good question, but the only thing I can think is that it would be difficult to make such a torpedo because of water. Most, at least what I’m familiar with, torpedos are relying on sonar and will go after the first thing that’s in its path. Missiles use radar, heat, lasers, and so on, making it easier for them to be precise. I’m not an expert in this so I could be way off, but that’s my take on it.

They are currently under development, with at-sea testing expected to begin next year. As for why there are no ATTs in the fleet today, the technological hurdles are high.

Well maybe, but i do recall reading and i honestly can’t remember where that it’s pretty hard to spoof a torpedo. That the only real defense for a submarine under attack is to turn and run at flankspeed and hope it runs out of fuel. Basically, that all these decoy devices submarines can deploy are pretty much useless and are just there for show.

Even if that’s not true no modern torpeso has (As far as i’m aware) any decoy abilities. It’s a large object moving fast through the water propelled by a very high speed propellar. That’s got to make enough noise to be a good target surely?

A ship or submarine is a large object. A torpedo is a small object. And it’s REALLY moving. It presents a very small cross section as it comes at you. Sound takes time to move through the water, and that time varies with conditions. Redsland is right. The technological hurdles are high.

It would be rather difficult to detect a supersonic torpedo before it struck your submarine.

Well ok hammerbach but.

  1. Isn’t the same true of a missile cross-section and they seem to be interceptable and aren’t most torpedos much bigger. Plus what if rather than homing on active sonar i.e. getting a return off the torpedo body ( which i’m still not convinced is impossible) you use a passive sonar setup with the defensive torpedo homing on the scew sound.

  2. They’re not going that fast. 60 knots or so which when you consider that

  3. Ok sound is slower than light but it still goes around 1500 m/s through water.

I’ve certainly got the impression (and i realise this may not be true) from novels that a decent sonar can detect an incoming torpedo 1000’s of yards away. Even hear them being launched. Which would leave plenty of time for a counter-launch.

I’m not sure the ATT’s passive sonar would work very well if it were traveling at 60 knots (although I’m certainly no expert). I don’t know if a passive sonar could be accurate enough at close range, either. I suspect you’d only get one chance with your ATT, as having missed, it would take some doing to have it turn around and catch up.
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As to the cross section of missiles, etc., I suspect that sucessful AMMs are not fired from the original missile’s target; the intercept courses would not be comparable. (All SWAG, I’m afraid…) And those tests are far from being usually sucessful. And do those AMMs get targeted at active missiles, or ballistic (no longer under powered flight)? Thier courses might be much more predictable.
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Point is that there’s a LOT to this, more than first meets the eye. I would be very impressed by a sucess in this field, and I’m sure someday I will be. But it will be challenging.

Since a torpedo is a moving target, you must know not only its position but also its velocity (speed and course).
It takes several measurements to obtain these informations.
In an anti-missile system, you rely in the fire control radar, wich makes several measurements by second, so you are able to track the incoming threat and take the effective countermeasures.
Sonars are much slower devices. An active sonar can only make a new measurement when the echo of its transmission arrives. Since the sound travels at 1500 m/s in water, the measurement of a target 15 km away will take 20 seconds (the sound goes to the target, then comes back).
A passive sonar can make measurements much faster (typically 0.5 seconds), but since it only provides bearing measurements, the ship must maneuver in order to have distance and velocity informations. This is feasible when tracking another ship, but not an incoming torpedo.

Deptford;

Missiles are largely irrelevant to this discussion. They travel at supersonic speeds, and torpedoes don’t. They travel through a consistent medium, and torpedoes don’t. They can be spotted hundreds of miles away, and torpedoes can’t. Their paths can generally be predicted quite accurately, and torpedos’ can’t. There are other differences, as well.

It’s true that torpedoes will give you a small active return and a larger passive return, as you’ve noted. But that actually works against your ATT. Because unless you heard the incoming torp when it was at great distance, your ATT is probably going to be moving at full speed. That means that it can’t use a passive seeker to find its target. It’ll have to go active. So your ATT will be forced to ignore all that noise the target is making, and try to find its small active return instead.

There are other challenges. Like the fact that your ATT has to be able to find targets, even though you didn’t lock onto them at firing. Once in the water, it has to discriminate among whatever objects it sees out there, including surface ships, submarines, debris, decoys, and marine life to locate the torpedo(s), prioritize them if there are several, track them, work out an intercept solution, close the distance, and make the kill. All in the time it takes two weapons to cross a few thousand yards at full speed.

And why does the ATT have to do all of these things autonomously? Because you can’t help it out. You went to flank speed when you launched, so your passive array is deaf and your active is pointed in the wrong direction. You can’t help the ATT find the fast little metal tube. And you have to merely trust that it will NOT find the fast BIG metal tube by mistake.

But none of those issues are the really tricky ones. Acquisition is straight-forward, if difficult. Target discrimination is software. What’s hard is closing in and making the kill. The attacking torp’s route is not necessarily predictable, because some torpedoes can be “flown” by hand. If your ATT is going against one of these, it could compute an intercept course and execute it, only to find that the torp zigged somewhere else. (Plus the points Sergio made.)

So that’s kind of an abridged oversimplification of the situation.

I would like to return to the subject of missiles briefly, though. I think you’re under the impression that anti-missile defense is something we’re good at. I hope one day we are, but that day is not at hand. The only system we currently have that I would call “reliable” is the ship-mounted close-in weapons system. It’s a last line of defense that shoots a stream of bullets at incoming missiles, hoping one hits. It often does, but you can see how different this system is from the torp/ATT system under discussion.

Thanks Redsland that makes alot of sense. Especially the fact that a ATT racing through the water will deafen itself. I had completely forgotten going fast deafens sonar sensors, which is why the subs in the techno-thrillers i obviously haven’t been paying close enough attention too, often use sprinting short distances and stopping to listen as a tactic.

Am I mistaken, or do some submarines carry decoys for exactly this purpose?

If you can defeat an approaching torpedo with a simple (and relatively cheap) semi-passive system, there’s much less incentive to design an active, extremely complex solution that attacks the torpedo, especially when a first-generation version would be less reliable than current decoy designs.

I’m not saying we’ll never have them. In fact, I think supercavitating torpedoes could revolutionize submarine warfare and lead to a whole new type of undersea combat, as air-to-air missiles did for air combat. I’m just saying that until they’re as cheap and nearly as reliable (or much more reliable and only a little more expensive) we’ll probably continue to use decoys.

Found this document about the very subject

www.noesis-inc.com/news/surface_ship_torpedo_defense.pdf+Effectiveness+of+torpedo+decoys&hl=en&ie=UTF-8]review of current thinking
Interesting read i thought.

That link is broken, Deptford.

Anoher factor not yet elaborated on is the physical engineering of a submarine versus a surface ship. Submarines are entirely enclosed vessels (you’d hope so, anyway) and the limitations on what shape and form they can take and what internal space can be dedicated to new systems are significant. You can’t just slap an ATT launcher on the outside of a submarine. It has to be inside the submarine, and you need outer and inner doors for the launching system, all of which presents significant design challenges. You’re either going to have to build a bigger boat, which then makes the sub less stealthy and hence less effective, or you’re going to have to sacrifice something to fit the ATT system in, which makes it less effective for that reason.

The difficulty of adding anti-missile systems to a surface ship isn’t anywhere near the same. Not to minimize the space limitations on a missile destroyer, but it’s obviously easier to do, since many ships had anti-missile systems added after initial construction (a lot of this happened after the Falklands war demonstrated the vulnerability of ships to missiles.)

My wife works on a WWII era submarine, and some of the volunteers that work with her are WWII submarine vets. There were two things on a submarine that would cloak their location. The first prevented bubbles from coming from the screws on the sub, and the other was that the decks were made of teak wood - which sinks if it is separated from the sub. But the torpedoes had no such precautions. You could see a torpedo coming from a long distance away, and the sub’s location could be traced back to the that point. This fact, plus the fact that subs had a limited number of torpedoes, meant that you used them sparingly.

The vets have told her that when a ship saw a torpedo coming they would change direction, and sometimes they would dump as many depth charges as possible in the hopes that the torpedo would strike one. The depth charges just sink, but the torpedoes back then had a basic navigation system where they would lock on to a magnetic target and follow it. This led to atleast one US sub being sunk by their own torpedo during the war. The depth charges were to atleast halt the torpedo before it went any further.

Just for your information.

This is a super old zombie, but bumping to add they’ve developed and deployed these devices on super carriers several years back. Here’s a good article about it and how it works: