On June 24, 1944, U.S. Navy warplanes patrolling the Atlantic attacked and sank a Japanese submarine, the I-52. It was an event of enormous strategic importance. The I-52"s mission was to return to Japan with the ingredients of a radiological bomb. Purchased from the Germans, this doomsday weapon-classified secret by the U.S. government for years after the war-could have contaminated vast areas of America for decades, killing millions slowly and painfully. Japan had intended to use it in an attack on the California coast until the mission was detected in an Allied intelligence coup equal to the breaking of the Enigma code. The I-52"s resting place was discovered in 1995 by ship salvager Paul R. Tidwell. Author Richard N. Billings has worked with Tidwell-whose attempts to salvage the I-52"s precious gold cargo continue-in bringing her secret mission to light. Finally, this is the story of how the I-52 mission may have influenced President Truman"s decision to drop atomic bombs on Hiroshima and Nagasaki.