Hunting submarines with magnets

SUBMARINES rely on stealth to do their jobs, whether that is sinking enemy ships or hiding nuclear-tipped missiles beneath the ocean. The traditional way of hunting them is with sonar. Modern sonar is extremely sensitive. But modern submarines are very quiet, and neither side has gained a definitive upper hand.

There are other options. Submarine-spotting aircraft carry “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.