Also, large fields were laid in the Atlantic off the coasts of Trinidad and North Africa and in the Mediterranean off the coast of Sicily. Although there is no record of any of the enemys ships being sunk or damaged in the Navys defensive fields, neither is there any record of the enemys ships passing through the fields. Perhaps the knowledge that the fields existed prevented any attempts being made, thus proving the adage that mines work well even when they don't work at all. During the Korean War, American forces were prevented from landing at Wonson for over a week in 1950 until 3,000 Communist mines could be cleared. Both surface and air mine countermeasures forces were deployed to find and neutralize primitive Iranian mines.
Bottom mines are influence activated and rest at the bottom of shallow areas of water.
Moored mines are effective against submarines as well as surface ships and are placed at a pre-determined depth under the water. Drifting mines, which were banned under the Hague Convention of 1907, move freely through the water. A moored mine that has lost its tether cable becomes a drifting mine. Bottom Mines are most effective in comparatively shallow waters. In very deep waters, surface vessels may pass over the mine without actuating its firing mechanisms or, in the event of actuation, without suffering much damage.