Book excerpt: The I-400 submarine was one of the most monstrous creations to emerge from World War II and, in its time, it was the largest submarine ever built. At more than 400 feet long, weighing 5,223 tons submerged, carrying a crew of nearly 200 and possessing a range of over 30,000 nautical miles, the I-400 featured state-of-the-art Japanese radar and 'stealth' technology and carried three Aichi M6A Seiran attack floatplanes in a water-tight tube-like hangar built onto the deck forward of and under its massive conning tower. In mid-1944 this secret weapon was tasked with attacking American cities and destroying the Panama Canal. The extraordinary story of this submarine is told using first-hand accounts from three of the original air crew assigned to fly the Seirans and former officers and crew of the I-400 as well as American naval personnel who crewed the vessel on its dramatic final voyage. Hundreds of remarkable photographs show external and internal views of the I-400, its hangar, aircraft, armament and equipment, and form a unique reference source for enthusiasts of World War II aviation and naval history.