sentences:  Ability of a submarine to submerge under that depth would require several layers of contact-fuzed mines at differing depths to afford equal probability of destruction.The World War I mine barrage had reduced the number of mines required by using a copper wire antenna with a float to extend it above the mine.A ship's steel hull touching the copper antenna would form a battery, and seawater acted as an electrolyte completing a circuit with an insulated copper plate on the mine surface to actuate a detonating relay within the mine.