The submarine included radar and radar detectors and watertight hanger for three Aichi M6A1 Serian seaplanes. The submarine had a range of 37,500 nautical miles. Construction began on January 18, 1943 at Kure Dock Yards under heavy security. Completed on December 30, 1944 and assigned to Captain Tosho Kusaka.
During 1945, the Japanese Navy planned a daring operation to use the I-400, I-401, I-13 and I-14 on a mission across the Pacific to the west coast of Panama to surface and launch M6A1 Seiran floatplanes to bomb the Panama Canal to disable the locks and delay shipping from crossing into the Pacific Ocean. Later, the mission was revised to have the M6A1 Seiran aircraft painted in U. S. markings and to be a Kamikaze mission to crash into the locks to cause maximum damage but the operation was never executed.
Instead, in June 1945 the target was switched to the U. S. Navy (USN) anchorage at Ulithi Atoll. This operation code-named Arashi (storm) would utilize only I-400 and I-401 and the M6A1 Seiran would be painted in U. S. markings and be a kamikaze mission to crash into any aircraft carriers in the anchorage. On July 23, 1945 both I-400 and I-401 departed Ominato and proceeded individually to their rendezvous point. On August 5, 1945 while at sea, I-400 suffered an electrical fire that forced it to surface to repair the damage. On August 14, 1945 reached the rendezvous point roughly 100 miles miles south of Ulithi Atoll but was not able to locate I-401. The attack was planned for August 17, 1945.
On August 15, 1945 Japan surrendered. When I-400 Captain Tosho Kusaka learned of the surrender, he ordered his submarine's M6A1 Seiran aircraft to be jettisoned overboard and decided to return to Kure Harbor to surrender the submarine.
On August 27, 1945 I-400 was spotted off
northern Honshu by Avengers from the USS Bennington and was pursued by USS Blue DD-744 and Mansfield DD-728 and surfaced and was boarded. On August 28, 1945 the USS Weaver DE-741 arrived to accept the surrender of the submarine. Afterwards, proceeded to Pearl Harbor to be evaluated by the U. S. Navy.
On June 4, 1946 off Barber's Point on Oahu sunk by torpedo fired by USS Trumpetfish SS-425 on during a tests of the Mark 10-3 exploder. After being hit by three Mark 18-2 electric torpedoes, the sub sank in deep water at 12:10, sinking by the stern. Over the course of several days four captured subs were sunk including I-201, I-14, and I-401.
After the discovery of I-401 on March 17, 2005, efforts were made to locate the wreckage of I-400. During August 2013, the Pisces submersible from University of Hawaii's Hawaii Undersea Research Laboratory's (HURL) discovered the submarine lying flat on the sea floor at 2,300' / 700m.
On March 16, 2016, the submarine's bell was recovery by HURL Pisces IV and Pisces V during a collaboration between University of Hawai‘i School of Ocean and Earth Science and Technology, Chico State University, Naval History and Heritage Command and the USS Bowfin Submarine Museum.
Air & Space Magazine "All and Nothing" November 2001 Issue, pages 22 - 31
I-400: Japan's Secret Aircraft-Carrying Strike Submarine: Objective Panama Canal by Henry Sakaida, Gary Nila and Koji Takaki
CNN "Hangar of Japan's aircraft carrier sub found"
May 5, 2015
UHawaii "Bronze bell recovered from World War II aircraft-carrying submarine off Oahu coast" March 16, 2016
YouTube "HURL submersibles recovery I-400 brass bell" March 16, 2016
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May 26, 2019