Underwater Missiles

By Deane Barker on April 2, 2006

I watched a story on CNN today about Iran having tested “the world’s fastest underwater missile.” It got me wondering just what an “underwater missle” was. Isn’t that called a “torpedo”?

Apparently not. There was a video which showed the missile launch from the end of a pier or dock of some kind and drop into the water. It was rocket propelled, just like a missile that flies through the air. The trail of bubbles was so fast the camera couldn’t keep up with it.

According to this article, it’s plenty fast:

The Iranian-made underwater missile has a speed of 223 miles per hour […] That would make it about three or four times faster than a torpedo […]

I’m guessing it doesn’t run that deep — perhaps just under the surface — so you’re not going sub-hunting with it. But with speed like that, any ship in the area has a big problem.

The fastest U.S. warship was the Pegasus class hydrofoil, all of which were decommissioned in 1993. At full power on their foils, they went about 46 m.p.h. A current Nimitz-class aircraft carrier runs at just over 30 m.p.h.

Now, 223 m.p.h, is fast, but still not nearly as fast as an airborne missle. The Exocet travels at just over 700 m.p.h. However, you can shoot an Exocet down using other missiles, or the aging Phalanx (“If it flies, it dies.”)

But what do you do about an underwater missile? It’s far too fast for a torpedo to intercept, so you’d have to have an “anti-underwater missile underwater missile.”

One possibility: an underwater bullet:

[a] 6.25 inch-diameter self-protection weapon is under study for the defense of surface ships and submarines using supercavitation technology. The Advanced High Speed Underwater Munition (AHSUM) program has already demonstrated the effectiveness of such high-speed underwater bullets. Fired from an underwater gun, these projectiles have successfully broken the speed of sound in water (1,500 meters per second), bringing their future application much closer to reality.

Regardless, given that Iran has 1,500 miles of coastline, naval duty in the Persian Gulf may never be the same again.



  1. PopSci had an article on future torpedo tech a few months ago. Apparently the next-gen torpedos might work by shooting compressed air ahead of the torpedo, creating a low-density pocket in which the torpedo can achieve supersonic speeds. Fins could project into the surrounding water to provide guidance.

    It all seems a bit like overkill in today’s environment, but I suppose that if I were a submariner, overkill would sound like a great idea.

  2. Some have speculated that it was just this sort of technology testing that felled the Kursk.

  3. A little off topic but …

    I once saw a show (Discovery Channel or TLC) about the building of an aircraft carrier. After it was built they took it out for testing which included turning the ship all the way port and starboard at full speed. I remember how crazy it was; the ship was banked over 30ยบ, carving a huge S-shaped wake in the ocean.

    Anyone know a place online with photos of such testing of aircraft carriers? How about commercial cruise ships?

  4. Such speeds are achieved under water using cavitation. Basically the tip of the torpedo/missile/whatever would have little openings out of which air/gas is released, thus creating a gaseous layer between the projectile and the water. This means that drag is greatly reduced and higher speeds are possible. It’s pretty hard to steer, however, and that makes the thing a pretty anachronistic weapon in modern naval warfare. Firing torpedoes in what basically amounts to a straight line at a even slowly moving targets is a tricky business, especially when your target is inclined to shoot back with more precise – albeit possibly slower – guided weapons.

  5. Couldn’t you just have a big & thick sheet of steel about 100′ from the ship plop in the water at the right time (or have it float there?), and have the missile detonate on that saving the ship?

    Especially when you can see the trail of bubbles.

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