By 1945, the U.S. Navy's submarine force in the Pacific had sunk over a thousand enemy cargo ships and tankers supplying the food, weapons, and oil Japan needed to continue to fight. Yet this once mighty merchant fleet continued to thrive in the Sea of Japan, where, protected from American submarines by a seemingly impenetrable barrier of deadly minefields, they provided a tenuous lifeline for the Japanese. With no knowledge of the secret development...