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US Navy boffins say they have made a significant breakthrough in countermeasures against sea mines - by using superconductors to nullify the magnetic signature of an American destroyer.

The Office of Naval Research (ONR) says that high-temperature superconductor (HTS) "degaussing" coils fitted to the destroyer USS Higgins were first turned up to full earlier this month in trials off San Diego, and worked successfully.

The ONR describes its new high(er)-temperature superconductor degaussing kit as a "cloaking device", and notes correctly that three-quarters of US naval vessels put out of action by enemies since 1950 have been victims of mines. Famously, Saddam Hussein's forces were able to knock out a US cruiser and a helicopter carrier - USS Princeton and USS Tripoli - in the Gulf War of 1991 using mines: inflicting far more naval damage than they sustained.

"Finding better ways to mitigate the threat of naval mines is something the whole program team takes a lot pride in because we know our work will save lives," says George Stimak of the ONR. "HTS degaussing technology will provide new options to the naval architect in designing future advanced degaussing systems."

In this context, "high" temperature is actually very cold. The Higgins' ceramic superconductor degaussing coils actually have to be kept chilled to -240°C in order to function. But this is worth doing, according to the ONR, because the much greater flux density which can be generated by a superconductor can generate a given magnetic field - necessary to cancel out that of the ship's ferrous structure - for less power and less weight.

"The superconductivity of this new degaussing system means less energy is required, yet it enables greater degaussing performance," according to Brian Fitzpatrick, an engineer who worked on the system. "Additionally, there is significant weight saving – up to 80 percent in some cases."

That does sound worthwhile: but it may be a while before superconductor degaussing becomes universal. Steel warships have been fitted with copper degaussing coils ever since magnetic mines came in, during WWII. No new "cloaking device" is on offer, just a somewhat refined one.

And degaussing isn't really a cloaking device against sea mines anyway. Simple buoyant mines which are triggered by a ship banging into them are still very common; others, generally laid on the sea bed like magnetics, sense the noise a vessel makes as it passes overhead. Still others detect the pressure wave caused by the target vessel's hull passing over. Modern designs often use two or three different sensors.

Even if you are up against purely magnetic mines, degaussing - no matter how good - is only a partial protection. It isn't practical to eliminate a large steel ship's signature altogether: thus minehunting ships, designed to work in minefields, are made of wood, glass-reinforced plastic or stainless steel - and have enhanced degaussing coils too.

Then, the weight and power consumption of existing degaussing coils aren't all that significant in the context of warship design: the DG coils aren't all that big a headache for naval architects to put in, or for the ship's generators either.

So superconductor degaussing probably isn't going to revolutionise naval mine warfare - which is three-quarters of modern naval warfare, much though you wouldn't know it from being in a modern navy. But it is interesting, all the same. ®

Lewis Page was a Minewarfare and Clearance Diving Officer in the Royal Navy until 2004.

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