Show magnetic kibies no terror to british menace soon ended by use of charged cables LOND LONDON ON the british navy revealed part ol of the story of its victorious battle over german magnetic mines a battle which w was a s joined the night of november 2 24 4 1939 when a live magnetic mine was captured convinced in the previous month that the nazis were using magnetic mines to destroy shipping the british were at a loss to establish countermeasures ter measures until a specimen was hauled from the sea that specimen showed how the mechanism worked and gave technical figures of the strength and duration of the magnetic field required to fire it out of a pool of schemes there came what the navy called double L or double longitudinal sweep this consisted of two ing ships each towing a long tail of self buoyant electric cable through which surged current generated on the ship and stored temporarily in batteries traveling in parallel courses with the floating tails stretched behind them the minesweepers were able to subject 10 or more acres of sea bottom to magnetic field of sufficient strength and duration to explode all mines in the area and thus provide a safe channel calling the method per cent effective the navy told how the first experiment was made one wintry day late in december 1939 when two tugs filled with motor car batteries went out from the harbor towing cable used for charging submarine marine batteries and floated on logs originally intended to make ship masts that trial confirmed the scientists calculations of the current through the sea and of the magnetic field that night orders went out from the admiralty for a large program of production which eventually overcame the menace of the magnetic mine |