Submarine I-400

IJN I-400 was the lead ship of the Sen-Toku (潜特型) class, the largest submarine class of World War II and the largest submarines ever built until the nuclear ballistic missile submarines of the 1960s. Built at Kure Naval Arsenal, she was laid down on 18 January 1943, launched on 18 January 1944 and commissioned on 30 December 1944. She displaced 5,223 tons surfaced and stretched 122 meters in length.

The submarine carried three Aichi M6A1 "Seiran" floatplane attack bombers stored in a watertight cylindrical hangar forward of the conning tower. Originally conceived by Admiral Yamamoto to strike American cities and attack the Panama Canal, the mission was altered in 1945 to Operation Arashi, a strike on the US fleet anchorage at Ulithi Atoll planned for 17 August 1945. However, Japan's surrender was announced before the mission could be executed.

I-400 surrendered at sea east of Honshu on 27 August 1945 to the destroyers USS Blue and USS Mansfield. She was later taken to Hawaii for technical examination by the U.S. Navy.

She was scuttled by three torpedoes from USS Trumpetfish off Pearl Harbor on June 4, 1946, to prevent Soviet inspection. Her wreck was located in August 2013 by the Hawaii Undersea Research Laboratory at a depth of about 557 meters southwest of Oahu.