Spring, 1946. Ten months after the end of World War II, an explosion rocks the Pacific off the coast of Hawaii. America has just destroyed one of Japan’s most advanced weapons systems – the I-401 aircraft carrier submarine. But this was no belated attack against the defeated Japanese. Bound by an agreement to share any discoveries with the Soviets but feeling the pressure of the looming cold war, it was a calculated decision to keep the technology out of Soviet hands.