View source for Japanese submarine I-401

{{Short description|1st class submarine of the Imperial Japanese Navy}}
{|{{Infobox ship begin}}
{{Infobox ship image
|Ship image=I400 2.jpg
|Ship caption=''I-401'' in 1945
}}
{{Infobox ship career
|Hide header=
|Ship country=Japan
|Ship flag= {{shipboxflag|Japan|naval}}
|Ship name=''I-401''
|Ship namesake=
|Ship ordered=
|Ship builder=[[Sasebo Naval Arsenal]], [[Sasebo]],&nbsp;[[Japan]]
|Ship laid down=26 April 1943
|Ship launched=11 March 1944
|Ship completed=8 January 1945
|Ship acquired=
|Ship commissioned= 8 January 1945
|Ship decommissioned=
|Ship in service=
|Ship out of service=
|Ship struck=15 September 1945
|Ship homeport=
|Ship honours=
|Ship fate=*Surrendered 29 August 1945
*Sunk as target 31 May 1946
|Ship notes=
}}
{{Infobox ship characteristics
|Hide header=
|Header caption=
|Ship class={{sclass|I-400|submarine}}
|Ship displacement=*{{convert|5223|LT|t|0|abbr=on}} surfaced
*{{convert|6560|LT|t|0|abbr=on}} submerged
|Ship length={{convert|122|m|abbr=on}}
|Ship beam={{convert|12|m|abbr=on}}
|Ship draft={{convert|7|m|abbr=on}}
|Ship propulsion=*[[Diesel-electric]]
*4 diesel engines, {{convert|7700|hp|abbr=on}}
*Electric motors, {{convert|2400|hp|abbr=on}}
|Ship speed=*{{convert|18.75|kn|mph km/h|lk=in}} surfaced
*{{convert|6.5|kn|mph km/h|abbr=on}} submerged
|Ship test depth= {{convert|100|m|abbr=on}}
|Ship range={{convert|37500|nmi|km|lk=in|abbr=on}} at {{convert|14|kn|mph km/h|abbr=on}}
|Ship complement=144
|Ship sensors=
|Ship EW=
|Ship armament=*8 × {{convert|533|mm|in|0|abbr=on}} forward [[torpedo tube]]s
*20 × [[Type 95 torpedo]]es
*1 × [[14 cm/40 11th Year Type naval gun]]<ref name="campbell">Campbell, John ''Naval Weapons of World War Two'' {{ISBN|0-87021-459-4}} p.191</ref>
*3 × {{Convert|35|mm|in|1|abbr=on}} 3-barrel machine gun
*1 × [[Type 96 25&nbsp;mm AT/AA Gun|Type 96 {{convert|25|mm|in|abbr=on}}]] machine gun
|Ship aircraft=3 × [[Aichi M6A|Aichi M6A1 Seiran]] sea-planes
|Ship aircraft facilities=
|Ship notes=
}}
|}
{{nihongo|'''''I-401'''''|伊号第四百一潜水艦|I-gō-dai yon-hyaku-ichi-sensuikan}} was an [[Imperial Japanese Navy]] [[I-400-class submarine|''Sentoku''-type (or ''I-400''-class)]] submarine commissioned in 1945 for service in [[World War II]]. Capable of carrying three two-seat [[Aichi M6A]]1 "Seiran" (Mountain Haze) [[Floatplane|float]]-equipped [[torpedo bomber]]s, the ''Sentoku''-class submarines were built to launch a surprise air strike against the [[Panama Canal]]. Until 1965, the ''Sentaku''-type submarines — ''I-401'' and her [[sister ship]]s {{ship|Japanese submarine|I-400||2}} and {{ship|Japanese submarine|I-402||2}}  — were the largest submarines ever commissioned.

==Design and description==

The ''I-400''-class submarines had four {{convert|1680|kW|hp|abbr=on}} [[diesel engine]]s and carried enough fuel to circumnavigate the world one-and-a-half times. Measuring {{convert|122|m|ft|abbr=on|0}} long overall, they displaced {{convert|5900|tonne|ST|abbr=on|0}}, more than double their typical American contemporaries.<ref name="Japanese naval vessels, article 7. Submarines, supplement 2">{{cite book|title=Japanese naval vessels|publisher=US Navy|year=1946}}</ref> Until the [[Ship commissioning|commissioning]] of the [[United States Navy]] [[ballistic missile submarine]] {{USS|Benjamin Franklin|SSBN-640}} in 1965, the ''I-400''-class were the largest submarines ever commissioned.<ref name=combinedfleetI401>{{cite web |url= http://www.combinedfleet.com/I-401.htm |title=IJN Submarine I-401: Tabular Record of Movement |first1=Bob |last1=Hackett |first2=Sander |last2=Kingsepp |work=combinedfleet.com |year=2011|access-date=24 October 2020}}</ref>

The cross-section of the [[pressure hull]] had a unique figure-of-eight shape which afforded the strength and stability to support the weight of a large, cylindrical, watertight aircraft [[hangar]], {{convert|31|m|sp=us}} long and {{convert|3.5|m|sp=us}} in diameter, located approximately amidships on the top deck. The [[conning tower]] was offset to port to allow the stowage of three [[Aichi M6A]]1 ''Seiran'' ("Clear Sky Storm") [[Floatplane|float]]-equipped [[torpedo bomber]]s along the centerline.<ref name="Japanese naval vessels, article 7. Submarines, supplement 2"/><ref name=Sakaida74>Sakaida, p.74</ref> Aircraft were launched from a {{convert|120|ft|m|disp=flip|adj=on|sp=us|0}} [[Aircraft catapult|catapult]] on the forward deck forward of the hangar. A collapsible crane allowed the submarine to retrieve her floatplanes from the water.<ref name=Sakaida81>Sakaida, p. 81</ref>

In addition to the three [[floatplane]]s, each ''I-400''-class submarine was armed with eight {{convert|533|mm|in|adj=on|sp=us|0}} [[torpedo tube]]s, all in the [[Bow (ship)|bow]], with 20 [[Type 95 torpedo|Type 95]] [[torpedo]]es,<ref name="Japanese naval vessels, article 7. Submarines, supplement 2"/><ref name=Sakaida17>Sakaida, p. 17</ref> a Type 11 {{convert|140|mm|in|adj=on|abbr=on}} deck gun aft of the hangar, three waterproofed [[Type 96 25 mm AT/AA Gun|Type 96]] triple-mount [[antiaircraft gun]]s mounted atop the hangar — one forward and two aft of the conning tower — and a single Type 96 25&nbsp;mm antiaircraft gun mounted just aft of the [[Bridge (nautical)|bridge]].<ref name=Sakaida100-101>Sakaida, p.100-101</ref>

''I-400''-class submarines had a rather noisy special trim system that allowed them to loiter submerged and stationary while awaiting the return of their aircraft;<ref name="Japanese naval vessels, article 7. Submarines, supplement 2"/><ref name=Layman178-179>Layman and McLaughlin, p. 178–179.</ref> [[Magnetization|demagnetization]] cables meant to protect against [[Naval mine|magnetic mines]] by nullifying the submarine′s [[magnetic field]];<ref name=Sakaida73>Sakaida, p. 73</ref> an air search [[radar]], two air/surface-search radar sets, and a [[radar warning receiver]];<ref name=Sakaida104-107>Sakaida, p. 104-107</ref> and an [[anechoic]] coating<ref name="Boyd, Carl 2002 pp. 27, 29">Boyd, Carl, and Yoshida, Akihiko, ''The Japanese Submarine Force and World War II'', BlueJacket Books (2002), {{ISBN|1557500150}}, pp. 27, 29</ref> intended to make detection of the submarine while submerged more difficult by absorbing or diffusing [[sonar]] pulses and dampening reverberations from the submarine's internal machinery.<ref name="Boyd, Carl 2002 pp. 27, 29"/><ref name=Sakaida92>Sakaida, p. 92</ref><ref name=Sakaida126>Sakaida, p. 126</ref>

==Construction and commissioning==

Ordered as '''''Submarine No. 5232''''',<ref name=ijnsubsiteI401>{{cite web |url= http://www.ijnsubsite.info/I-Sub%20Details/I-401.htm |title=I-401 ex No-5232 |work=iijnsubsite.info |year=2019|access-date=24 October 2020}}</ref> ''I-401'' was [[Keel-laying|laid down]] on 26 April 1943 by the [[Sasebo Naval Arsenal]] at [[Sasebo]], [[Japan]].<ref name=combinedfleetI401/><ref name=ijnsubsiteI401/> She was [[Ceremonial ship launching|launched]] on 11 March 1944,<ref name=combinedfleetI401/><ref name=ijnsubsiteI401/> and was completed and [[Ship commissioning|commissioned]] on 8&nbsp;January&nbsp;1945<ref name=combinedfleetI401/><ref name=ijnsubsiteI401/> with [[Lieutenant Commander]] [[Nobukiyo Nambu]] in command.<ref name=combinedfleetI401/><ref name=ijnsubsiteI401/>

==Service history==
===World War II===
====January–May 1945====
Upon commissioning, ''I-401'' was attached to the [[Kure Naval District]] and assigned to Submarine Division 1 — which also included her [[sister ship]] {{ship|Japanese submarine|I-400||2}} and the submarines {{ship|Japanese submarine|I-13||2}} and {{ship|Japanese submarine|I-14||2}} — in the [[6th Fleet (Imperial Japanese Navy)|6th Fleet]].<ref name=combinedfleetI401/><ref name=ijnsubsiteI401/> She also was assigned to Submarine [[Squadron (naval)|Squadron]] 11 for workups.<ref name=combinedfleetI401/> The [[flagship]] of Submarine Division 1, she got underway from Sasebo on the day of her commissioning to begin workups in the western [[Seto Inland Sea]] with ''I-13'' and ''I-400''.<ref name=combinedfleetI401/> She was at [[Kure, Hiroshima|Kure]], Japan, on 19 March 1945 when the [[United States Navy]]′s [[Task Force 58]] launched the first [[Allies of World War II|Allied]] air strike against the [[Kure Naval Arsenal]].<ref name=combinedfleetI401/> More than 240 aircraft from the [[aircraft carrier]]s {{USS|Essex|CV-9}}, {{USS|Intrepid|CV-11}}, {{USS|Hornet|CV-12}}, {{USS|Wasp|CV-18}}, {{USS|Hancock|CV-19}}, {{USS|Bennington|CV-20}}, and {{USS|Belleau Wood|CVL-24}} attacked Japanese ships in the harbor at Kure.<ref name=combinedfleetI401/> American aircraft [[Strafing|strafed]] ''I-401'', but she was not damaged.<ref name=combinedfleetI401/>

On 11 April 1945, ''I-401'' put to sea from Kure with the commander of Submarine Division 1, [[Captain (naval)|Captain]] Tatsunosuke Ariizumi, embarked bound for [[Dairen]], [[Manchukuo]], where she was to load [[fuel oil]] for transportation back to Japan.<ref name=combinedfleetI401/> ''I-401'' ran aground shortly after leaving port, but freed herself and continued her voyage.<ref name=combinedfleetI401/> On 12 April 1945, however, she detonated a [[Naval mine|mine]] laid by a [[United States Army Air Forces]] [[Boeing B-29 Superfortress|B-29 Superfortress]] in the Iyo Nada in the Seto Inland Sea {{convert|750|m|yd|sp=us|sigfig=2}} northeast of the [[Himeshima, Ōita|Himeshima]] [[lighthouse]], bearing 037 degrees from the lighthouse.<ref name=combinedfleetI401/> The explosion damaged some of her instruments and her aft [[ballast tank]] valves, forcing her to turn back to Kure for repairs.<ref name=combinedfleetI401/> She underwent repairs during May 1945, and [[shipyard]] workers installed a [[Submarine snorkel|snorkel]] aboard her while she was under repair.<ref name=combinedfleetI401/>

====Panama Canal operation====

By 1 June 1945, all four submarines of Submarine Division 1 had been fueled and equipped with snorkels. They got underway from Kure that day for a voyage via the [[Shimonoseki Strait]], the [[Tsushima Strait]], and the [[Sea of Japan]] to [[Nanao Bay]] on the western coast of [[Honshu]] near [[Takaoka, Toyama|Takaoka]], Japan.<ref name=combinedfleetI401/> After they arrived in Nanao Bay on 4 June 1945, six [[Aichi M6A]]1 ''Seiran'' ("Clear Sky Storm") aircraft of the Kure-based 631st Naval Air Group joined them, flying in after a stop at [[Fukuyama, Hiroshima|Fukuyama]], Japan.<ref name=combinedfleetI401/> On 6 June 1945, the submarines and aircraft began training for night air operations in preparation for a surprise Japanese air strike against the [[Panama Canal]] in which the submarines would launch ten M6A1 [[floatplane]]s, which were to strike the [[Gatun Locks]] from the east with six [[torpedo]]es and four [[Aerial bomb|bombs]], emptying [[Gatun Lake]] and blocking the [[canal]] to shipping for months.<ref name=combinedfleetI401/> During training, the Japanese demonstrated that four trained men could prepare one of the floatplanes for launch from a submarine in seven minutes and that each submarine could assemble, fuel, arm, and launch all three of the floatplanes it carried in 45 minutes.<ref name=combinedfleetI401/> Despite various obstacles — the presence of mines and U.S. Navy submarines and shortages of [[aviation gasoline]] — the submarines and aircraft launched a number of simulated air strikes.<ref name=combinedfleetI401/>

While Submarine Division 1 was still at Nanao Bay, the expected imminent fall of [[Okinawa Island|Okinawa]] to U.S. forces and the increasing pace of air strikes by [[Allies of World War II|Allied]] aircraft carriers on the [[Japanese archipelago|Japanese Home Islands]] prompted Japanese [[Imperial General Headquarters]] to cancel the Panama Canal strike on 12 June 1945 and decide instead to use the submarines and their floatplanes to strike the Allied fleet anchorage at [[Ulithi]] in the [[Caroline Islands]].<ref name=combinedfleetI401/> The submarines and aircraft completed their flight training on 19 June 1945, with all of the M6A1 floatplanes taking off from the waters of Nanao Bay that day.<ref name=combinedfleetI401/> One failed to return, and the bodies of its two crewmen later washed ashore on [[Sadogashima]].<ref name=combinedfleetI401/>

====Operation Arashi====

At 13:25 on 25 June 1945, the [[Combined Fleet]] issued orders for the attack on Ulithi, dubbed [[Operation Arashi]] ("Mountain Storm").<ref name=combinedfleetI401/> The orders called for ''I-13'' and ''I-14'' to transport [[Nakajima C6N]]1 ''Saiun'' ([[Cloud iridescence|Iridiscent Cloud]]"; [[World War II Allied names for Japanese aircraft|Allied reporting name]] "Myrt") [[reconnaissance aircraft]] to [[Chuuk Lagoon|Truk]] in the Caroline Islands in late July 1945.<ref name=combinedfleetI401/> In [[Operation Hikari]] ("Shining Light"), the C6N aircraft were to conduct a reconnaissance of Ulithi, noting the presence and location of Allied aircraft carriers and [[Troopship|troop transport]]s.<ref name=combinedfleetI401/> ''I-400'' and ''I-401'' then were to launch a combined total of six M6A1 floatplanes — which were to use the reconnaissance information to assist them in targeting Allied ships — on 17 August 1945 for a nighttime strike under a full moon against the Ulithi anchorage, each pilot receiving a [[hormone]] injection to improve his [[night vision]] and each plane armed with an {{convert|800|kg|lb|adj=on|sp=us|0}} bomb.<ref name=combinedfleetI401/> After the strike, the aircraft were to land near the submarines, and ''I-13'', ''I-14'', ''I-400'', and ''I-401'' all were to proceed to [[Singapore]], where ten new M6A aircraft would await them for embarkation for another strike.<ref name=combinedfleetI401/>

On 13 July 1945, ''I-401'' departed Nanao Bay bound for [[Maizuru]], Japan, which she reached the same day.<ref name=combinedfleetI401/> She began to load ammunition and three months of provisions.<ref name=combinedfleetI401/> After a farewell ceremony for the aircraft crews on 18 July 1945 at the Shiraito Inn at Maizuru attended by the commander-in-chief of the 6th Fleet, [[Vice Admiral]] [[Tadashige Daigo]], ''I-400'' and ''I-401'' got underway for [[Ōminato Guard District|Ōminato]] in northern Honshu on 20 July 1945, escorted by a [[minesweeper]].<ref name=combinedfleetI401/> ''I-401'' reached at Ōminato on 21 July 1945<ref name=combinedfleetI401/> and ''I-400'' on 22 July,<ref name=combinedfleetI400>{{cite web |url= http://www.combinedfleet.com/I-400.htm |title=IJN Submarine I-400: Tabular Record of Movement |first1=Bob |last1=Hackett |first2=Sander |last2=Kingsepp |work=combinedfleet.com |year=2016|access-date=25 October 2020}}</ref> and after their arrival their crewmen received a day of shore leave, the aircraft had their Japanese markings replaced with American ones, and each submarine brought aboard a model of the Ulithi anchorage as a training aid for the pilots.<ref name=combinedfleetI401/> ''I-400'' departed Ōminato at 14:00 on 23 July 1945, followed by ''I-401'' at 16:00.<ref name=combinedfleetI401/> The two submarines took separate routes in the [[Pacific Ocean]] far to the east of Japan, planning to rendezvous off [[Pohnpei|Ponape]] in the Caroline Islands on 16 August 1945.<ref name=combinedfleetI401/>

Only a little over four hours into her voyage, ''I-401'' was on the surface in [[Tsugaru Strait]] at 20:15 on 23 July 1945 when two [[Imperial Japanese Army]] [[coastal artillery]] [[Artillery battery|batteries]] on the coast of [[Hokkaido]] at [[Cape Shiokubi]] mistook her for an Allied submarine and opened fire on her with [[Type 96 15 cm howitzer]]s.<ref name=combinedfleetI401/> After one of the [[Shell (projectile)|shells]] landed only {{convert|300|m|yd|sp=us|sigfig=2}} off her [[Port and starboard|port]] quarter, {{nowrap|''I-401''}} submerged.<ref name=combinedfleetI401/> After exiting Tsugaru Strait at 06:30 on 24 July 1945, she surfaced, and Ariizumi transmitted a message protesting the coastal artillery bombardment.<ref name=combinedfleetI401/> ''I-401'' weathered a [[typhoon]] on 28 and 29 July 1945, and in late July she sighted an unescorted American [[Tanker (ship)|tanker]], but did not attempt to attack it so as to avoid compromising Operation Arashi.<ref name=combinedfleetI401/> On 31 July 1945, ''I-401'' was off [[Marcus Island]] when Ariizumi ordered her to remain on the surface and proceed at {{convert|19|kn}} to make up for lost time and arrive at the rendezvous with ''I-400'' on schedule.<ref name=combinedfleetI401/>

Concerned by high levels of activity by American aircraft and surface ships near the planned rendezvous point, Ariizumi decided on 14 August 1945 to alter course to the east of the [[Marshall Islands]] and meet ''I-400'' at a new location {{convert|100|nmi}} south of Ponape that evening.<ref name=combinedfleetI401/> He transmitted the new plans in a coded message to ''I-400'', but ''I-400'' never received the message,<ref name=combinedfleetI401/> and when ''I-401'' surfaced at the rendezvous point 30 minutes after sunset, ''I-400'' was nowhere to be found.<ref name=combinedfleetI401/> According to contingency plans, if the submarines missed their rendezvous, they were to attempt another meeting south of Ulithi at 03:00 on 17 August 1945 and launch their air strike, so ''I-401'' made for that rendezvous point.<ref name=combinedfleetI401/> Meanwhile, Ariizumi consulted with the 6th Fleet and a consensus was reached to postpone the Ulithi raid until 25 August 1945.<ref name=combinedfleetI401/>

On 15 August 1945, [[Emperor of Japan|Emperor]] [[Hirohito]] announced that hostilities between Japan and the Allies would end that day.<ref name=combinedfleetI401/> The senior officers aboard ''I-401'' did not view the announcement as credible and decided to continue with the planned attack on Ulithi,<ref name=combinedfleetI401/> and early on the morning of 16 August 1945 ''I-401'' headed for the rendezvous with ''I-400''.<ref name=combinedfleetI401/> When she surfaced after sunset on 18 August 1945, however, she received orders from the 6th Fleet to cancel the attack, and later that day she was ordered to proceed to Kure.<ref name=combinedfleetI401/> Although her crew urged her officers to head for Truk instead and continue fighting, Ariizumi decided that she would proceed to Nanao Bay or Ōminato, after which her crew would [[Scuttling|scuttle]] her to avoid surrendering her to the Allies, and she headed for Japan.<ref name=combinedfleetI401/>

====End of war====
On 26 August 1945, ''I-401'' received orders to hoist a black flag of surrender and to disarm herself.<ref name=combinedfleetI401/> Accordingly, her crew assembled all three of her M6A1 aircraft and [[Aircraft catapult|catapulted]] them unmanned into the sea, dumped their bombs overboard, fired all of her torpedoes, and destroyed all of her [[Logbook|logs]], [[Nautical chart|charts]], [[codebook]]s, and secret documents.<ref name=combinedfleetI401/>

''I-401'' was in the Pacific Ocean off the [[Sanriku Coast|Sanriku]] Bight east of [[Honshu]] on the night of 28–29 August 1945 when the U.S. Navy submarine {{USS|Segundo|SS-398}} detected her on [[radar]], and at around midnight ''I-401''′s lookouts sighted ''Segundo'', which they identified as a suspicious vessel.<ref name=combinedfleetI401/> ''I-401'' worked up to full speed in an attempt to break contact, but her port [[diesel engine]] broke down at dawn on 29 August 1945 and ''Segundo'' ordered her to stop.<ref name=combinedfleetI401/> Her [[navigation officer]] went aboard ''Segundo'', whose crew told him that ''I-401'' must surrender.<ref name=combinedfleetI401/> When Nambu received this information, he contacted [[Tokyo]] at 05:00 for instructions and received orders to surrender his submarine.<ref name=combinedfleetI401/> A [[prize crew]] from ''Segundo'' made up of ''Segundo''′s [[executive officer]] and five enlisted men then boarded ''I-401'', and ''I-401''′s crew presented them with a bottle of [[Suntory]] [[whiskey]].<ref name=combinedfleetI401/>

After ''I-401''′s hatches were chained open to prevent her from submerging without sinking, ''Segundo''′s prize crew ordered her to proceed to [[Yokosuka]], Japan, with ''Segundo''′s executive officer in command.<ref name=combinedfleetI401/> Ariizumi insisted that ''I-401'' instead make for Ōminato and scuttle herself there, but after Nambu disagreed and obeyed the American orders to head for Yokosuka, Ariizumi committed suicide in his cabin, shooting himself with his pistol while ''I-401'' was in the [[Philippine Sea]] off [[Izu Ōshima]] on 30 August 1945.<ref name=combinedfleetI401/> {{nowrap|''I-401''′s}} crew wrapped his body in a flag and dumped it overboard through a hatch without the Americans noticing.<ref name=combinedfleetI401/> Ariizumi had committed [[war crime]]s while in command of the submarine {{ship|Japanese submarine|I-8||2}} during [[World War II]], and suspicions later arose that ''I-401''′s crew had put Ariizumi ashore near [[Sendai]] before she surrendered or that he had swum ashore in [[Tokyo Bay]] to avoid prosecution, but these theories were not proven.<ref name=combinedfleetI401/>

[[File:Japanese submarine I-14 in 1945.jpg|thumb|''I-401'' between the U.S. Navy [[submarine tender]] {{USS|Proteus|AS-19|6}} (left) and the Japanese submarine {{ship|Japanese submarine|I-14||2}} (right) after the end of hostilities in 1945.]]
''I-401'' and ''Segundo'' arrived in [[Sagami Bay]] on the coast of Honshu at 05:00 on 31 August 1945.<ref name=combinedfleetI401/> The American flag was raised on ''I-401'', and Nambu presented the officer commanding the prize crew with two ''[[katana]]'' as a symbol of surrender.<ref name=combinedfleetI401/> Later in the day, a new prize crew from the [[submarine tender]] {{USS|Proteus|AS-19}} came aboard ''I-401'' and relieved the ''Segundo'' prize crew, after which ''I-401'' proceeded to Yokosuka<ref name=combinedfleetI401/> and tied up along with ''I-14'' near ''Proteus'' and twelve U.S. Navy submarines chosen to represent the U.S. Navy Submarine Force at the [[Surrender of Japan|Japanese surrender ceremony]] in [[Tokyo Bay]].<ref name=combinedfleetI401/> At 08:00 on 1 September 1945, {{nowrap|''I-401''′s}} Imperial Japanese Navy [[Rising Sun Flag|battle flag]] was lowered, and during the surrender ceremony on 2 September 1945, the [[COMSUBPAC|Commander, Submarine Force, U.S. Pacific Fleet (COMSUBPAC)]], [[Vice Admiral (United States)|Vice Admiral]] [[Charles A. Lockwood]], ordered his personal flag hoisted aboard ''I-401''.<ref name=combinedfleetI401/>

===Postwar===

The Japanese struck ''I-401'' from the Navy list on 15 September 1945.<ref name=combinedfleetI401/> On 29 September 1945, the commander of U.S. Navy [[Task Force 38]], Vice Admiral [[John Henry Towers|John H. Towers]], inspected her.<ref name=combinedfleetI401/>

On 29 October 1945, ''I-401'' got underway from Yokosuka southbound for Sasebo with a 40-man American crew aboard in company with ''I-14'', ''I-400'', and the [[submarine rescue vessel]] {{USS|Greenlet|ASR-10}}.<ref name=combinedfleetI401/><ref name=combinedfleetI400/> The ships encountered a heavy storm during their voyage, and the American crews of ''I-400'' and ''I-401'' noted that the ''I-400''-class submarines′ double-hull construction allowed them to ride remarkably smoothly in the heavy seas.<ref name=combinedfleetI401/> The vessels arrived at Sasebo on 1 November 1945.<ref name=combinedfleetI401/>

After loading Japanese [[Motor vessel|motor]] [[Launch (boat)|launches]] onto their decks to serve as [[Lifeboat (shipboard)|lifeboats]],<ref name=combinedfleetI400/> ''I-400'', ''I-401'', and ''I-14'' departed Sasebo on 11 December 1945<ref name=combinedfleetI401/> under escort by ''Greenlet''<ref name=combinedfleetI400/> bound for [[Pearl Harbor]], [[Hawaii]], stopping along the way at [[Apra Harbor]] on [[Guam]] in the [[Mariana Islands]] from 18 to 21 December 1945, then at [[Eniwetok]] in the Marshall Islands, and then at [[Kwajalein]] for food and supplies from 26 to 27 December 1945.<ref name=combinedfleetI401/> They arrived at Pearl Harbor on 6 January 1946 and tied up at the Submarine Base, where a U.S. Navy band and local celebrities welcomed them.<ref name=combinedfleetI401/> On 16 January 1946, ''I-401'' conducted exercises with the submarine {{USS|Puffer|SS-268}} and ''I-401'' and ''I-14'' conducted radar tests with the submarine {{USS|Steelhead|SS-280}}.<ref name=combinedfleetI401/>

==Disposal==

With postwar relations with the [[Soviet Union]] deteriorating rapidly and concerns growing in the [[United States]] that under postwar agreements the Soviets would demand access to the captured Japanese submarines that would provide the [[Soviet Navy]] with valuable information about advanced Japanese submarine designs, the U.S. Navy issued orders on 26 March 1946 to sink all captured Japanese submarines.<ref name=combinedfleetI401/> Accordingly, the U.S. Navy sank ''I-401'' as a target in tests of the Mark 10 Mod 3 exploder off Pearl Harbor on 31 May 1946.<ref name=combinedfleetI401/> She sank by the [[stern]] at 10:59 at {{coord|21|1|N|158|07|W|name=''I-401''}} after the submarine {{USS|Cabezon|SS-334}} hit her with two [[Mark 18 torpedo]]es.<ref name=combinedfleetI401/>

==Discovery of wreck==
On 17 March 2005, the [[Hawaii Undersea Research Laboratory]]'s (HURL) deep-diving submersibles ''Pisces IV'' and ''[[Pisces V]]'' located {{nowrap|''I-401''}} off  [[Kalaeloa, Hawai'i|Kalaeloa]], Hawaii. ''I-401'' lies at a depth of {{convert|820|m|ft|0}} off [[Barbers Point]].<ref>[https://www.wrecksite.eu/wreck.aspx?146997 wrecksite.eu IJN I-401 (+1946)]</ref> The submersibles found ''I-401''′s [[Bow (ship)|bow]] broken off just forward of the aircraft [[hangar]] and lying not far from the rest of the [[Hull (ship)|hull]], connected to it by a [[debris]] field. The submersibles found the hull sitting upright on the sea floor, and the name ''I-401'' was clearly visible on the sides of the [[conning tower]]. ''I-401''′s [[Type 96 25 mm AT/AA Gun|Type 96 25 mm]] [[anti-aircraft gun]]s appeared to be in almost perfect condition.

==References==
{{reflist}}

==Bibliography==
* [[Henry Sakaida|Sakaida, Henry]] and Gary Nila, Koji Takaki. ''I-400: Japan's Secret Aircraft-Carrying Strike Submarine''. Hikoki Publications, 2006. {{ISBN|978-1-902109-45-9}}

==External links==
* [https://web.archive.org/web/20150216111748/http://www.soest.hawaii.edu/HURL/gallery/archaeology/I-401.html HURL I-401 page]
* [https://www.pbs.org/wnet/secrets/episodes/japanese-supersub-watch-the-full-episode/591/ Japanese SuperSub]  Documentary produced by the [[PBS]] Series [[Secrets of the Dead]]

{{I-400 class submarine}}
{{April 1945 shipwrecks}}
{{1946 shipwrecks}}

{{DEFAULTSORT:I-401}}
[[Category:Submarine aircraft carriers]]
[[Category:I-400-class submarines]]
[[Category:1944 ships]]
[[Category:Ships built by Sasebo Naval Arsenal]]
[[Category:World War II submarines of Japan]]
[[Category:Maritime incidents in April 1945]]
[[Category:Maritime incidents in 1946]]
[[Category:Ships sunk as targets]]
[[Category:Shipwrecks in the Pacific Ocean]]