To be fair, the magnetic influence exploder was the "wonder weapon" of submariners in the pre-war period and was being developped by the Kriegsmarine and the Royal Navy as well. The same concept was used in British, American and German magnetic mines. It was not all the U.S. Navy's fault since Congress had cut military budgets to the bone in the 20's (disarmament) and 30's (depression) which severely limited live testing. The Kriegsmarine which had an unlimited budget after 1933 still wound up with a malfunctioning torpedo MI in 1939.
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