The attack on Pearl Harbour was just the first half of Japan's plan to bring the US to the bargaining table. The second phase involved a reign of terror to shatter American morale through sustained air strikes against the East Coast, launched from the decks of three gigantic submarines. Yeah, from submarines.
Known as the the Sen Toku I-400-class Imperial Japanese Navy submarine and invented by Japanese Combined Fleet Commander-in-Chief Adm. Isoroku Yamamoto, these hybrid weapons of war machines were designed to take advantage of both their aircraft's fast strike capabilities and the sub's natural stealth. Three I-400's were built during the war, with another two nearly finished, though none of them actually saw combat.
At 400 feet long, 40 feet wide, 23 feet tall, and displacing 6,560 tons the Sen Toku's are among the largest subs ever built—60 percent larger than their contemporary American submarine, the USS Argonaut, and offered double its operational range. Each Sen Toku carried three M6A1 Seiran floatplane bombers, which would be launched from the sub's double-reinforced deck using a catapult assisted 84 foot runway. 157 officers, engineers, electricians, and pilots were needed to command the vessel . "It is the only submarine that carried fighters," Masanori Ando, who works at the JMSDF Submarine Training Center in Kure told Stars and Stripes. "There is no other example."
Unfortunately for Japan, by the time the third Sen Toku launched in 1945, the war was nearly over. Two of the subs, I-400 and I-401, were dispatched to Ulithi atoll to attack Allied troops there but arrived just in time to discover Emperor Hirohito had surrendered. Both subs were captured and sailed back to America for study after the war. However when Russia demanded similar access to the technology, the US scuttled both of them in secret around 1946 rather than hand them over to the Soviets.
For the next 68 years, I-400 sat at the bottom of the Pacific before it was rediscovered off the coast of Oahu earlier this month by Hawaii Undersea Research Laboratory explorer Terry Kerby and colleagues from the NOAA and the University of Hawaii at Manoa's School of Ocean and Earth Science and Technology. [Stars and Stripes, Combined Fleet, Wiki, Live Science]