Find out why one of the most powerful tools of the Second World War was never used.
One of the best-kept secrets of the Second World War was a huge aircraft-carrying submarine designed to deliver Japanese bombers to within a few hundred kilometres of American cities.
Engineers and historians conduct experiments and demonstrations to reveal the secrets behind a technological marvel that could have changed the course of the war.
Plus, archive footage shows what made the I-400 subs so deadly: the three state-of-the-art attack bombers it could carry anywhere in the world. But why was the technology never used in an attack on the US?
Japan's Secret Weapon
One of the best-kept secrets of World War II was Japan's plan to bomb the Panama Canal with an innovative secret weapon unlike anything its enemies possessed: a massive, aircraft-carrying submarine capable of traveling around the world to deliver its deadly attack bombers against land-based targets.