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With this technology, it is even possible to work out the approximate size of a vessel passing above a subsea cable, as well as its location and, in some circumstances, its direction of travel.

"The number of cable faults per year has really held steady over the last several years," she adds, explaining that the 1-200 faults that typically occur annually has not risen despite ever more subsea cables being installed during that period.

It was during tests of AP Sensing's system last year – not a real attempt at sabotage – that the diver patted his hand on the subsea cable watched over by the firm.

Unlike some other methods, in which heavy subsea equipment is tethered to support ships, Impossible Metals' vessel would not have to remain in a precise spot for a long period, meaning its engines would not create as much noise.

The company said it has developed more than 20 subsea cables with partners over the last decade.