Naval mine
Counter-mining

Another expedient for clearing mines, especially in a hurry, is counter-mining. By this method an explosive is detonated in the area of a known or suspected minefield and the blast either trips off the fuses or the actual explosive contained within the mine or mines. This latter is known as a sympathetic detonation. Counter-mining is normally used as a last resort or if other equipment is not available. One example was at the entrance to Grand Harbour, Valletta, Malta in WW2 when the British dropped depth charges into the harbour entrance to detonate suspected mines prior to the arrival of an important convoy. It is especially useful against acoustic or pressure mines due to their activation by sound or increases in water pressure.
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