I-400 Class Submarine
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
HURL March 17, 2005
The submarine included radar and radar detectors and watertight hanger for three Aichi M6A1 Serian seaplanes. Laid down on September 29, 1943 at Kobe. Completed and commissioned on January 8, 1945, assigned to Captain Ariizumi.
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. Both subs departed Ominato on July 23, 1945.
The sub was accidentally fired upon by friendly shore batteries at the Tsugaru Strait, but suffered no damage. After passing through a storm, the sub spotted aircraft and screw noise near Marcus Island, forcing them to detour to the east, and sent a message to I-400 to rendezvous 100 miles south of Ponape, but the other sub failed to receive it. The strike date was set for August 17, but Japan surrendered on 15th.
After hearing of the surrender, the Captain elected to return to Yokosuka, to surrender in Japanese home waters. They jettisoned their Serain aircraft. USS Segundo SS-398 located her on radar and negotiated for the sub's surrender. On the voyage back, the captain Ariizumi committed suicide, and the sub was surrendered by its LtCdr Nambu. Sailed to Hawaii, and evaluated
by the US Navy.
On May 31, 1946 at 10:59am off Barber's Point on Oahu, sunk by two
torpedoes from the USS Cabezon (SS-334), testing the Mark 10-3 exploder in deep water. Over the course of several days four captured subs were sunk including I-201, I-14, and I-400.
On March 17, 2005, a University of Hawaii's Hawaii Undersea Research Laboratory's (HURL) submersible discovered the submarine lying flat on the sea floor at 2665'. It was identified from the I-401 painted on the side of the coning tower. The submersible recorded video and stills of the wreck.
Some items were taken by USN prior to its sinking and survive today. The Yokohama WWII Japanese Military Radio Museum has two items from the I-401 on display: gun site and M6A1 Serian bombsite. Probably, both items were removed by Americans prior to the sinking and sold.
Air & Space Magazine "All and Nothing" November 2001 Issue, pages 22 - 31
HURL: I-401 Found off Barber's Point
I-400: Japan's Secret Aircraft-Carrying Strike Submarine: Objective Panama Canal by Henry Sakaida, Gary Nila and Koji Takaki
National Geographic "Hunt for Samurai Subs" November 17, 2009
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August 7, 2015
21 12 N
158 07 W