sentences:  The Mk XX mine became available in early 1941 with a copper wire antenna extended above the explosive casing by a buoyant float and a lower antenna extending below the casing.Minelaying progressed with new fields laid north and south of the Faeroes and in the Denmark Strait using Mk XX mines wherever its depth coverage would reduce the number of mines required.Additional safety measures were required for the new mines after "Menestheus" was damaged by detonation of a drifting Mk XX mine on 6 February 1941.