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  I-400 Japanese Submarine
I-400 Class Submarine
Sentoku Type

5,223 Tons (surfaced)
6,560 Tons (submerged)
122m x 12m x 7m
8 x torpedo tubes
1 x 140mm deck gun
bridge 25mm AA gun
3 x 3x25mm AA gun
3 x M6A1 Seirans
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USN August 27, 1945

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USN June 4, 1946

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USN June 4, 1946

Ship History
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.

Wartime History
The Japanese Navy planned to use the I-400 along with the I-401, I-13 and I-14 to participate in a daring plan to attack the Panama Canal and disable its locks. In June 1945 the decision was made to switch targets to hit USN anchorage at Ulithi Atoll. The plan was code-named Arashi (storm) for the I-400 and I-401 to use its Serians on Kamikaze attacks on any carriers based there. The two subs departed Ominato on July 23, 1945. At sea, the sub suffered an electrical fire on August 5th that forced it to surface to repair the damage, but successfully reached their rendezvous point, 100 miles miles south of Ulithi on August 14th, but the I-401 was not there. The strike date was set for August 17th, but Japan surrendered on the 15th.

After hearing of the surrender, the Captain elected to return to Kure, to surrender in Japanese home waters. They jettisoned their Serain aircraft. Spotted on August 27th off northern Honshu by Avengers from the USS Bennington. Destroyers USS Blue DD-744 and Mansfield DD-728 pursued the sub and boarded it to accept its surrender. The following day, the USS Weaver DE-741 arrived to again accept its surrender. After surrender, the sub was sailed to Hawaii, and evaluated by the US Navy.

Sinking History
On June 4, 1946 off Barber's Point on Oahu sunk 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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Last Updated
February 4, 2018


21 13 N
158 07 W

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