The Problematic Magnetic Exploder
The U.S. Navy innovation was supposed to result in the ultimate submarine weapon—a torpedo that would explode under a ship. That sort of attack would snap a small ship in half and bypass the layers of side compartments that were supposed to protect a larger ship—such as a battleship or carrier—against torpedo hits. The magnetic exploder, which responded to a sharp increase in the earth’s magnetic field caused by a passing ship, was such a closely held secret that it had a cover name: the Index Device. The usual demonstration for submarine officers was to pass a metal cigarette case near a magnetic exploder. A click would be heard. If something as small as the case could trigger the exploder, surely any warship also would do so.