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As submarines rely on stealth to complete their various missions, it is difficult to trace them.  

Traditionally, submarines can be hunted by sonar. But although modern sonar is extremely sensitive the new submarines are very quiet, and neither side has gained a definitive upper hand.

Another solution is the submarine-spotting aircraft that carries “magnetic anomaly detectors” (MAD) which pick up disturbances in the Earth’s magnetic field caused by a submarine’s metal hull. Those disturbances are tiny, which means MAD is only useful at ranges of a few hundred metres.

According to economist.com, a new technology might make hunting submarines possible, by using the magnetic signatures of their wakes. Seawater is salty, full of ions of sodium and chlorine. Because those ions have different masses, any nudge—such as a passing submarine—moves some farther than others. Each ion carries an electric charge, and the movement of those charges produces a magnetic field. The US navy and a company named Contana have tried to develop the technology basing on the Debye Effect.

But it is likely that the technique can only detect certain submarine movements in some situations. Submarines produce many different types of wake. As well as the familiar V-shaped wake they leave underwater disturbances known as “internal waves”, flat swirls called “pancake eddies” and miniature vortices which spin off from fins and control surfaces. These all depend not only on speed and depth but also on the submarine’s hydrodynamics .

It is early days for the technology, at least in the West. But work done in Russia, whose navy has long been interested in alternatives to sonar, suggests the Debye effect can be turned into something quite potent.

Russian publications suggested that a well-tuned Debye detector might be able to pick up a trail from several kilometres back and follow it to find the submarine. Russia’s claims in this area have long been regarded in the West as exaggerated. The new American interest suggests they might not have been, economist.com evaluates.

Now, a new generation of high-tech magnetic sensors based on machines called SQUIDs—“superconducting quantum interference devices”—should be more sensitive than existing ones. Both the US and Britain are in the midst of replacing their present generation of nuclear-armed submarines. The new boats will be some of the quietest ever built. But if their wakes give them away, that may not matter.