Deperming, or degaussing, is a procedure for erasing the permanent magnetism from ships and submarines to camouflage them against magnetic detection vessels and enemy marine mines. A sea-going metal-hulled ship or submarine, by its very nature, develops a magnetic signature as it travels, due to a magneto-mechanical interaction with Earth's magnetic field. This signature can be exploited by magnetic mines, or facilitate the detection of a submarine by ships or aircraft with magnetic anomaly detection (MAD) equipment. Navies use the deperming procedure, in conjunction with degaussing, as a countermeasure against this.