Discusses the top-secret Japanese submarine project in World War II, creating submarines designed to work as underwater aircraft carriers, and the planned attack on U.S. cities that could have changed the outcome of the war.

Prologue. Face-off ; The I-401 -- Preparation. Birth ; Nambu ; Underwater aircraft carriers ; Proof of concept ; Challenges -- Complications. Reduction and revival ; Nambu under fire ; Nambu becomes a mole ; Seiran takes flight ; The Panama Canal ; Ariizumi ; Ariizumi under fire -- The Segundo (SS 398) ; Decline -- Mission. Nambu and the I-401 ; The 631st ; Fulp on patrol ; Kure ; Adversity ; Attacking the Canal ; Green light ; Fulp's last patrol ; Nanao Bay ; The taste of persimmon ; Johnson takes command ; Operation Storm -- Race against time. Departure ; Under way ; Crossed wires ; The Emperor's voice ; Anarchy ; Escape ; Interception ; Spoils of war ; Reckoning ; Boarding party ; The tenth war god ; Bittersweet ; Freedom ; The long road home ; Rediscovery.