Japan's Most Secret Weapons of World War II

The I-400 ‘super submarine' (and her two sister boats), was one of the most monstrous creations to emerge from the Second World War and, in its time, they were the largest submarines ever built. It was considered to have been one of Japan's most secret weapons – indeed the Allies remained unaware of the 1-400s existence until it surrendered in late August 1945 (along with the I-401). At more than 400 feet long, weighing 5,223 tons submerged, carrying a crew of nearly 228 and possessing a range of over 37,500 nautical miles, the I-400 featured state-of-the-art Japanese radar and ‘stealth' submarine technology and carried three Aichi M6A Seiran attack floatplanes in a water-tight tube-like hangar built on to its deck forward of and under its massive conning tower.

In mid-1944, the General Staff of the Imperial Japanese Navy tasked the I-400 and its sister boats with a secret mission to attack American cities and to destroy the Panama Canal. Further plans included a strike on the American aircraft carriers of Task Force 38 at Ulithi Atoll in the Western Caroline Islands.