(Sen Toku Type submarine by Takeshi Yuki)
IJN Submarine I-400:
Tabular Record of Movement
© 2001-2015 Bob Hackett & Sander Kingsepp
9 January 1944:
18 January 1943:
Kure Navy Yard. Sen-Toku class I-400 is laid down as the largest submarine class in the world. The class will carry three two-seat Aichi M6A1 "Seiran" (Mountain Haze) float torpedo-bombers capable of carrying either 1,764 lbs. of bombs or a 45 cm. (17.7-inch) torpedo 654 miles.
Cdr Kusaka Toshio (former CO of I-26, I-174, I-180) is posted as the Chief Equipping Officer (CEO) of I-400.
18 January 1943:
During her construction it is planned to use the Sen-Toku to launch a surprise air strike against the Panama Canal. The plan calls for ten Seiran to strike the Gatun Locks from the east with six torpedoes and four bombs. Destroying these locks would empty Gatun Lake and block the passage of shipping for months.
15 December 1944:
Cdr Kusaka is posted as Commanding Officer (CO).
The 631st Kokutai is organized for the purpose of attacking the Panama Canal. Only two M6A1 Seiran
are available for the air unit.
30 December 1944:
I-400 is completed and registered in the Kure Naval District. She is assigned to Vice Admiral Miwa Shigeyoshi's (former CO of CL KINU) Sixth Fleet in Captain Ariizumi Tatsunosuke's (former CO of I-8) SubDiv 1 with I-13, I-14 and I-401.
Western Inland Sea. I-400 begins workup and battle training at SubRon 11 with I-401 and I-13.
9/10 March 1945: The First Fire Bombing of Tokyo:
B-29s of MajGen (later Gen/CSAF) Curtis E. LeMay's Twentieth Air Force's XXI Bomber Command take off from Guam, Tinian and Saipan. 280 B-29's bomb Tokyo by radar at night. Dropping 1,900-tons of incendiaries from altitutes of 4,500 to 9,000 feet, they burn out about one-fourth of the city. At least 83,000 people die in the raid, the highest death toll of any day in the war, including deaths caused by the atomic bombs.
March - April 1945:
In retaliation for the fire bombing of Tokyo, the Imperial Naval General Staff considers a proposal from the Sixth Fleet to use I-400's to bomb San Francisco. The proposal is opposed by Vice Admiral Ozawa Jisaburo (former CO of HARUNA), Vice Chief, NGS.
19 March 1945:
Vice Admiral (later Admiral) Marc A. Mitscher's Task Force 58 carriers USS ESSEX (CV-9), INTREPID (CV-11), HORNET (CV-12), WASP (CV-18), HANCOCK (CV-19), BENNINGTON (CV-20) and the BELLEAU WOOD (CVL-24) make the first carrier attack on the Kure Naval Arsenal. More than 240 aircraft (SB2C "Helldivers", F4U "Corsairs" and F6F "Hellcats") attack battleships HYUGA, ISE, YAMATO, HARUNA, carriers AMAGI, KATSURAGI, RYUHO, KAIYO and other ships. I-13 crash-dives and escapes damage.
I-400, in drydock, and I-401 are strafed. During the attack, I-400 fires back from her Type 96 triple 25-mm AA gun. One gunner is killed in a strafing attack.
1 April 1945:
Vice Admiral (later Admiral) Raymond A. Spruance's Fifth Fleet, including more than 40 aircraft carriers, 18 battleships, 200 destroyers and over 1,000 support ships surround Okinawa. LtGen Simon B. Buckner Jr's Tenth Army (7th, 77th, 96th Infantry, 1st, 6th Marine divisions) makes amphibious landings and begins the campaign to take the island from LtGen Ushijima Mitsuru's 32nd Army.
5 April 1945:
Arrives at Moji.
6 April 1945:
Departs Moji for Kure.
12 April 1945:
I-401 departs Kure for Dairen, Manchukuo (Manchuria) to obtain fuel, but is damaged by a mine and forced to return to Kure for repairs.
14 April 1945:
I-400 departs Kure for Dairen with ComSubDiv 1 Ariizumi aboard.
20 April 1945:
Arrives at Dairen, embarks 1,700-tons of fuel oil made from liquified coal, soybean oil and ammunition.
23 April 1945:
27 April 1945:
Returns to Kure.
A "snorkel" breathing tube is installed to allow operation of the diesel engines while submerged.
1 June 1945:
All four of SubDiv 1's boats are fueled and equipped with snorkels.
2 June 1945:
Departs Kure for Nanao Bay.
5 June 1945:
Arrives at Nanao Bay for battle training. Six Seiran of the 631st NAG follow from Kure via Fukuyama.
6 June 1945:
Night flight training begins. A team of four trained men can prepare a floatplane for launch in seven minutes. All three Seiran carried aboard each submarine can be assembled, fueled, armed and catapulted in 45 minutes.
SubDiv 1's training is hampered by mines, American submarines and shortages of aviation gasoline, material and aircraft, but they manage to launch a number of simulated air strikes.
12 June 1945:
The Imperial High Command decides to use SubDiv 1 to attack the American naval anchorage at Ulithi Atoll because of the imminent fall of Okinawa and the carrier raids on Japan. The Panama Canal operation is formally discarded despite protests by Captain Ariizumi.
13 June 1945:
An M6A1 Seiran, being ferried from the Aichi factory to Nanao Bay crashes destroying the aircraft and killing its two crewmen.
19 June 1945:
Last day of flight training. All Seiran take off from the water, but one aircraft fails to return. Later, the bodies of its two crewmen are wash ashore at Sadoga Island.
21 June 1945: The Fall of Okinawa:
Eighty-two days after the initial landings, Okinawa is declared secure.
25 June 1945: Operation "Arashi" (Mountain Storm) - The Attack on Ulithi:
At 1325, Vice Admiral Ozawa Jisaburo, now CINC, Combined Fleet, issues Battle Order No. 95 that details the impending operation. The bombing attack is designated as Operation Arashi.
The "Hikari" (Shining Light) part of Operation Arashi calls for I-13 and I-14 to proceed to Truk in late July and deliver their Nakajima C6N1 Saiun ("Myrt") long range reconnaissance aircraft. The aircraft will then be assembled and used to reconnoiter Ulithi. The Myrt's will relay target information on American aircraft carriers and troop transports to I-400 and I-401's six Seiran torpedo-bomber crews for a strike on 17 August.
The attack is to be made under a full moon. Prior to the start of the attack, the pilots are to receive a special hormone injection to enhance their night vision. The Seiran are tasked to each carry an 800-kg bomb and land near their submarines. After the attack, all four of SubDiv 1's boats are to proceed to Singapore, refuel and embark new planes for the new attack. Ten Seiran are to be stationed there prior to the attack on Ulithi.
13 July 1945:
Departs Nanao with I-401, enters Maizuru harbor on the evening of the same day to evade air attacks. Embarks provisions for three months and ammunition.
18 July 1945:
Maizuru. A departure ceremony is held at the Shiraito Inn. Vice Admiral, the Marquis, Daigo Tadashige (former CO of ASHIGARA), CINC, Sixth Fleet, greets the 631st Kokutai aviators of I-400 and I-401 for a farewell sake toast and wishes them success.
20 July 1945:
Departs Maizuru for Ominato with I-401, escorted by a minesweeper. Just before the departure, the 631st Kokutai pilots receive their ritual short swords from Captain Ariizumi. Their unit is designated "Shinryu Tokubetsu Kogekitai" (Divine Dragon Special Attack Unit). I-400's Seiran pilots and navigators of Seiran No. 1 are Ensign Fukunaga Masayoshi and Lt Yoshimine Toru (Hikocho of I-400), No. 2 are CPO Wakasa Hideo and WO Shimaoka and No. 3 are CPOs Okuyama and Watanabe.
22 July 1945:
Arrives at Ominato. One-day of liberty is granted to all crews. Japanese markings are deleted from the Seiran and fake American "Stars and Bars" markings are applied. A model of the anchorage at Ulithi is taken aboard as a training aid for the pilots.
23 July 1945:
At 1400, I-400 departs Ominato for Ulithi, followed by I-401 at 1600. They take separate tracks far to the east for a rendezvous at sea on 16 August off Ponape Island, Carolines. I-400 misses a radio message from Ariizumi's flagship and proceeds to the wrong rendezvous point.
28 July 1945:
I-400 endues Typhoon weather conditions.
5 August 1945:
E of Saipan. I-400 suffers an electrical fire in a portside control panel. Cdr Kusaka orders "Emergency! Rapid Surface!" I-400's lookouts soon sight an American convoy in the distance. Kusaka orders a crash-dive. The fire is put out, but the boat is filled with smoke. Kusaka brings 1-400's conning tower to the surface and vents the submarine through open hatches. For the next five hours, I-400 sits just above the surface while her engineers perform repair repairs..
14 August 1945:
Aboard I-401, ComSubDiv 1 Captain Ariizumi decides to make a detour E of the Marshall Islands because of American air and surface activity. He sends a coded message to I-400 of the change and designates a new rendezvous point 100 miles S of Ponape. I-400 fails to receive the message and misses the rendezvous. 
15 August 1945:
The Imperial Palace, Tokyo. Emperor Hirohito (Showa) broadcasts an Imperial Rescript that calls for an end to the hostilities.
18 August 1945:
At 2100 (JST), Captain Ariizumi receives an order from Vice Admiral Daigo to cancel the operation. Later that day, I-400 and I-401 are ordered to return to Kure.
26 August 1945:
I-400 receives an order to hoist the designated black flag of surrender with a black ball and to disarm the boat.
The three M6A1 Seiran, with false American markings, are run out of the hangar, their bombs detached, then the aircraft are assembled, run up and catapulted unmanned into the sea. I-400s derrick drops the bombs into the ocean. All 20 Type 95 torpedoes are fired out and codes, logs, charts and secret documents are also destroyed.
27 August 1945:
At 1200, I-400, flying the black flag, is sighted by one of Task Force 38's aircraft. The plane reports I-400's location at 38-40N, 143-12E. I-400 surrenders to destroyers USS BLUE (DD-744) and MANSFIELD (DD-728) 500 miles NE of Tokyo.
Cdr (later Rear Admiral) Hiram H. Cassedy (former CO of USS SEARAVEN, SS-196 and TIGRONE, SS-419) and a prize crew of four officers and forty men disembark from Captain Charles N. Day's submarine tender USS PROTEUS (AS-19) and proceed towards I-400's location aboard USS WEAVER (DE-741).
28 August 1945:
WEAVER arrives alongside I-400. Cdr Cassedy assumes command of I-400. I-400 proceeds towards Yokosuka escorted by BLUE and WEAVER.
29 August 1945:
Sagami Wan. At 0915, I-400 under Cassedy's prize crew moors to port alongside PROTEUS. At 0955, I-14 arrives under Cdr Clyde B. Steven's prize crew and also moors to port outboard of the I-400.
30 August 1945:
At 0820, PROTEUS, I-400 and I-14 get underway enroute to Tokyo Bay and anchor there at 1458. Immediate1y on anchoring, Vice Admiral Charles A. Lockwood, Jr., COMSUBPAC, arrives on board PROTEUS. Lockwood is to represent the USN submarine forces at a formal surrender ceremony to be held three days later aboard USS MISSOURI (BB-63). Cdr (later Captain) William B. Sieglaff assumes command of I-400.
31 August 1945:
Tokyo Bay. At 0500, the American flag is raised aboard I-400. At 1445, PROTEUS, I-400 and I-14 get underway again to shift berths and proceed to within the breakwater of Yokosuka Naval Base in the lagoon adjacent to the Submarine Base. At 1650, PROTEUS is anchored bow and stern.
Twelve American submarines, also present to represent the submarine force, are tied on either side of Captain J. A. Jordan's PROTEUS. They are USS ARCHER-FISH (SS-311), PILOTFISH (SS-386), CAVALLA (SS-244), RAZORBACK (SS-394), GATO (SS-212), RUNNER (SS-476), HADDO (SS-255), SEA CAT (SS-399), HAKE (SS-256), SEGUNDO (SS-398), MUSKALLUNGE (SS-262) and TIGRONE (SS-419). I-401, an additional war prize, joins the group at this time. The huge Japanese I-boats dwarf the American fleet boats.
2 September 1945: The Formal Surrender of Japan.
Admiral Lockwood, aboard MISSOURI for the surrender, orders his personal flag hoisted over I-400 during the time the ceremony is held.
15 September 1945:
Removed from the Navy List.
29 October 1945:
I-400, under Cdr (later Captain) Joseph M. McDowell and a skeleton 40-man American crew, departs Yokosuka for Sasebo with I-401 and I-14 escorted by submarine rescue vessel USS GREENLET (ASR-10). 
A heavy storm arises while the ships are enroute south. The Americans find that I-400 rides remarkably smoothly even in rough seas due to her double hull construction.
1 November 1945:
Arrives at Sasebo.
11 December 1945:
Japanese motor launches are taken aboard the submarines as lifeboats prior to departure on their trans-Pacific crossing on the surface. I-400, under Cdr McDowell, departs Sasebo for Pearl Harbor with I-401 under Cdr (later Captain) Edward D. Spruance (former CO of USS LIONFISH (SS-298), son of Admiral Raymond A. Spruance and
I-14 under Cdr (later Admiral/ CINCPAC) John S. McCain, Jr. (former CO of USS GUNNEL (SS-253) and DENTUDA (SS-335), son of Vice Admiral (Admiral posthumously) John S. McCain. They are escorted by the GREENLET. Cdr Cassedy is the Squadron Commander.
18 December 1945:
Arrives at Apra Harbor, Guam.
21 December 1945:
Departs Guam for Eniwetok, Marshall Islands.
Arrives at Eniwetok.
26-27 December 1945:
Stops at Kwajalein to take on fuel and supplies.
6 January 1946:
Arrives at Pearl Harbor. I-400, I-401 and I-14 are met by a Navy band and local celebrities.
18 February 1946:
Dry-docked at Pearl Harbor for evaluation.
26 March 1946: Submarine Officers Conference, Washington, DC:
The attendees, including former ComSubPac Vice Admiral Charles A. Lockwood, are told that "orders are being issued to dispose of all Japanese submarines by sinking. Those in Japan will be sunk at once, those in Pearl Harbor when authorized by SCAP and at the discretion of CinCPAC
dispose of all captured Japanese submarines by sinking." 
4 June 1946:
I-400 is a target ship in the Pacific off Pearl Harbor for tests of the Mark 10-3 exploder. At 1210, she sinks by the stern at 21-13N, 158-07W after being hit by three Mark 18-2 electric torpedoes fired by Cdr D. B. Bell's new USS TRUMPETFISH (SS-425).
ComSubPac, Rear Admiral Allan R. McCann (former CO of IOWA (BB-61), ComSubRon 5, Captain (later Vice Admiral) Elton W. Greenfell (former CO of GUDGEON (SS-211) and ComSubDiv 52, Cdr/MOH (later Vice Admiral) Lawson P. Ramage (former CO of PARCHE (SS-384) are embarked on TRUMPETFISH and witness the I-400's sinking.
1 August 2013:
SW Oahu, Hawaii. The Hawaii Undersea Research Laboratory's (HURL) deep-diving submersible Pisces V locates the wreck of I-400 while investigating targets of interest previously identified by Terry Kerby, Steve Price and Chris Kelley of HURL. Pisces V’s crew includes submersible pilot Terry Kerby of HURL and Drs. James Delgado and Hans Van Tilburg of the National Oceanic and Atmospheric Administration’s (NOAA) Maritime Heritage Program.
The hull of the submarine is intact from bow to stern. What appeared to be the tip of the bow is actually about 50 feet back from the tip of the bow. The whole superstructure is missing and there are signs of massive implosion damage. It appears the 115ft long hangar and upper deck structure with conning tower separated from the main deck as I-400 descended to 1826 feet (562m).
For further details and photos of this find, please see our Special Feature Discovery of Imperial Japanese Navy Submarine (I-400) on SENSUIKAN!
30 October 2014:
| I-400's aft hatch and deck gun
|| Twisted launch ramp hanging over I-400's port bow |
| Starboard bow section where I-400's bow broke off
||I-400's stern, rudder, dive planes and screws|
HURL’s deep submersible research vessels Pisces 4 & 5 go back to I-400 with NHK and are able to find its missing hangar bay, conning tower and AA guns. They find the hangar in numerous pieces and mostly destroyed although there is one large section of it near the conn. The bridge tower is lying on its side with all three masts extended. It is in pretty good shape although the numbers on the side are difficult to see. The hangar bay door was one of the first things found. It is lying on the seabed. Of the AA guns, two are upside down and one is on its side. A survey was also done of the side of the hull where the torpedo hit. Researcher Terry Kerby located the ships bell on the seabed. The 70 minute NHK production ran about 7 May 2015.
| I-400 Hangar Door Cover
|| I-400 with HURL DSV at bow |
| “New” pic of I-400 & I-401 at Pearl
|| Covered 5.5 inch (140 mm)/50 cal. deck gun |
| Ship’s bell
|| Triple-mount AA guns |
 Sen-Toku remained the largest submarine class in the world until deployment of the 425-foot USS BENJAMIN FRANKLIN (SSBN-640) class ballistic missile nuclear submarines in 1965.
 See www.combinedfleet.com/ijna/m6a.htm
 The plan was to attack Ulithi on 17 August, but this was postponed until 25 August.
 The I-400 class was designed to normally carry a crew of 157 men; however, for some operations they carried in excess of 200 men.
 Reportedly, the I-400, I-401, I-14 and I-200 class submarines were sunk to prevent their technology being surrendered to the Russians under a war end agreement.
Thanks go to Andrew Obluski of Poland and Dr. Higuchi Tatsuhiro of Japan. Thanks also go to Derek Waller of UK for info about the Submarine Officers Conference.
Special thanks for photos of I-400's wreck go to Steve Price of the Hawaii Undersea Research Laboratory.
– Bob Hackett and Sander Kingsepp
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