Guerre di meraviglie

Acoustic mines are now being used by Germany in attempts to block English coastal waers, Prime Minister Churchill disclosed recently. Laid by night in the approaches to harbors, the latest mines are equipped with sound-detectors that pick up sound waves from a ship’s engines. The vibrations act on a vibrating reed, producing electrical impulses, and when these become powerful enough, due to the nearness of the ship, they set off the explosive charge contained by the mine.