World War II Database

Submarine I-401, along with her sister submarines, were the largest submarines in the world until 1965. Built at Sasebo, Japan, she was commissioned in Jan 1945 at Kure Naval District, Japan under the command of Lieutenant Commander Nobukiyo Nambu. She conducted training shortly after with Submarine Squadron 11 along with her sister submarine I-400. On 19 Mar 1945, during an American aerial attack on Kure, I-401 was strafed while in drydock but not damaged. On 11 Apr, she ran aground outside of Kure en route to Dairen, Manchuria, China, but was able to break free without damage. On the next day, she was hit by a naval mine, forcing her to return to Kure for repairs. In May, she was fitted with a breathing tube that allowed her diesel engine to operate while she was submerged. On 4 Jun, she arrived at Nanao Bay for training, launching six M6A Seiran aircraft operated by the 631st Naval Air Group.

I-401 was originally designed to attack faraway targets such as American coastal cities or the Panama Canal, but toward the end of the war when she was ready to launch an attack, a more realistic target was chosen. On 20 Jul 1945, she was dispatched from Maizuru harbor during Operation Arashi in a force of two I-400-class submarines (I-400 and I-401, each carrying three aircraft) and two modified AM-class submarines (each carrying two aircraft) to attack the American anchorage at Ulithi in the Caroline Islands. On 21 Jul, she arrived at Ominato, Honshu, Japan, where all crew were granted one day's leave while all submarines in the group were painted with fake American markings. On 23 Jul, she departed at 1600, taking a slightly different route toward Ulithi than the other submarines to avoid detection. En route, she encountered an American tanker without escort, but decided against attacking the tanker and jeopardizing the primary mission. On 14 Aug, she arrived at a rendezvous point near Ponape where she was to regroup with I-400, but I-400 was nowhere to be found; according to plan, the attack was postponed until I-400 arrived. Shortly after the postponement decision was made, the Japanese surrendered, ending the Pacific War. I-401's mission was aborted on 18 Aug. Some of her crew entertained the thoughts of heading to Truk in the Caroline Islands and continue fighting, but ultimately obeyed Nambu's decision to comply with the surrender order. She fired her 20 Type 95 torpedoes and launched their aircraft into the water on 22 Aug 1945 before surrendering to the Americans on 29 Aug. All of I-401's codes, logs, charts, and documents were also destroyed. She was surrendered to submarine USS Segundo; Lieutenant Muneo Bando, I-401's navigation officer, went aboard Segundo to notify the wish to surrender, and later Segundo sent a boarding party of one officer and five enlisted men to I-401, which was presented a bottle of Suntory whiskey. On 31 Aug, the american flag was raised aboard I-401 for the first time as the submarine formally surrendered. Nambu presented Segundo's executive officer Lieutenant J. E. Balson his samurai swords as symbols of surrender.

The Americans never learned of the existence of the I-400-class submarines until their crews surrendered. On 29 Sep, Vice Admiral John Towers of Task Force 38 conducted a personal inspection of I-401. I-400 and I-401 were studied by the United States Navy at Sasebo, Japan between 1 Nov and 11 Dec 1945 and then at Hawaii, United States between mid-Jan and May 1946. As the Russians increased their demands to evaluate the Japanese submarines as well, I-401 was scuttled off Kalaeloa as a target ship near Oahu, Hawaii on 31 May 1946 to prevent the Russians from doing so. She was sunk by two Mark-18 electric torpedoes fired by submarine USS Cabezon.

I-401's wreck was found by the Hawaii Undersea Research Laboratory's deep diving vehicles on 17 Mar 2005 at the depth of 820 meters. Her wreck lay in two separate pieces.

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