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  I-20 Japanese Submarine
Type C I-16 Class

358' 7" x 29' 10" x 17' 6"
2,184 Tons (surfaced)
3,561 Tons (submerged)
6 × 21" Torpedo tubes with 20 Type 95 Torpedoes
1 × 140mm deck gun
2 x 25mm Type 96 AA guns

Sub History
Built by Mitsubishi Shipbuilding in Kobe. Laid down November 16, 1937. Launched January 25, 1939. Commissioned on September 26, 1940 into the Imperial Japanese Navy (IJN) under the command of Commander Yamada Takashi and based in the Yokosuka Naval District. Assigned to SubRon 1's SubDiv 2, Sixth Fleet on January 31, 1941.

On November 17, 1941 at the Kure Naval Club, officers are briefed on "Operation Z" the Hawaii Operation. I-20 is assigned to the Special Attack Unit along with I-16, I-18, I-24 and flagship I-22.

Wartime History
On November 18, 1941 departs Kure as part of the Special Attack Unit for Kamegakubi Naval Proving Ground where each submarines embarks a Type A midget submarine code named "Mato", I-20 embarks her first HA-20 Type A Midget Submarine (Midget A). On November 19, 1941 at 2:15am departs Kamegakubi across the Pacific Ocean passing Midway bound for Oahu. On December 2, 1941 the submarine receives the coded signal to proceed with the attack.

On December 7, 1941 at 2:57am I-20 launches HA-20 Type A Midget Submarine (Midget A) roughly 5.3 miles off the entrance to Pearl Harbor on Oahu. Afterwards, I-20 proceeds to the recovery area south of Lanai. None of the midget submarines arrive and all are presumed lost. On December 8, 1941 in the morning departs for Kwajalein arriving with I-16 on December 20, 1942.

On January 4, 1942 departs Kwajalein to conduct a war patrol in the Samoa-Fiji area. On January 11, 1942 surfaces and shells Pago Pago.

On January 16, 1942 off Suva fires two torpedoes at HMNZS Monowai but both explode prematurely. As I-20 surfaces, she is fired on by the vessel's 6" guns but her deck gun fires and claims a hit on the bridge before the sumarine crash dives when straddled by shells. Both are undamaged, HMNZS Monowai sends a submarine altert signal reporting the contact. On January 24, 1942 returns to Kwajalein then departs for Yokosuka arriving February 1, 1942.

On April 16, 1942 part of the KO ("A") detachment with the I-10, I-18, I-20, I-30 and their support ships, the auxiliary cruisers/supply ships Aikoku Maru and Hokoku Maru. At Hiroshima Bay, Vice Admiral Komatsu, Captain Ishizaki their staffs and midget submarine crews pay a courtesy visit to Admiral Isoroku Yamamoto aboard his flagship Yamato. At 11:00, KO ("A") detachment departs for Penang.

On April 27, 1942 arrives at Penang as part of "A detachment" including I-16, I-18 and I-20 with Nisshin transporting Type A midget submarines. At Penang, each mother submarines is loaded with a Type A midget submarine, the second midget submarine embarked (the first was during "Operation Z" for the Hawaii Operation).

On April 30, 1942 departs Penang with "A detachment" bound for the Indian Ocean and to launch a midget submarine attack. Between May 5-15, 1942 the submarines are refuel at sea by Aikoku Maru and Hokoku Maru.

On May 17, 1942 while surfaced in the Indian Ocean southest of Madagascar heavy seas cause flooding in the engine room through the main induction valve. When the damage is repaired, the same compartment is flooded again and repaired. Despite the damage, the submarine continues the mission. On May 24, 1942 heavy shipping traffic is reported en route to the target area.

On May 29, 1942 Japanese submarines I-10, I-16 and I-20 are in position to attack Diego-Suarez Bay (Antsiranana Bay) on Madagascar. To perform a reconnaissance over the target area, I-10 launches her floatplane at 10:30pm spots HMS Ramillies, destroyers HMS Duncan, HMS Active, corvettes HMS Genista and HMS Thyme, troopship HMS Karanja, hospital ship HMS Atlantis, MV British Loyalty, merchant MV Llandaff Castle and an ammunition ship. Based on this report, Captain Ishizaki orders a midget submarine attack the next night.

On May 30, 1942 launches HA-20 Type A Midget Submarine (No.20b) under the command of Lt Saburo Akieda with crew PO1C Masami Takemoto to attack Allied ships in Diego-Suarez Bay (Antsiranana Bay). At 8:25pm, their midget submarine fires her first torpedo at HMS Ramillies that hits and causes damage. Afterwards, depth charged but at 9:20pm managed to fire her second torpedo at MV British Loyalty and sinks her in shallow water. Afterwards, this midget submarine beached at Nosy Antalikely and the crew were aided ashore by natives and attempt to reach the recovery area near Cape Amber (Cape d'Ambre). When they purchased food, their presence was reported to the British and both were killed in a firefight with Royal Marines three days later.

On May 31, 1942 in an attempt to locate any surviving midget submarine crew members and assess damage, I-10 launched her E14Y1 Glen floatplane piloted by piloted by Lt(jg) Shunshi Araki on another reconnaissance over Diego-Suarez Bay (Antsiranana Bay). On June 1, 1942 at 11:00pm

On June 3, 1942 at the recovery area near Cape Amber (Cape d'Ambre) I-20 surfaces and unsucessfully attempts to locate any surviving midget submarine crews by firing flares and sending radio transmissions without result and by 6:00pm departs the area.

5 June 1942: Commerce Raiding in the Indian Ocean:
The I-20 torpedoes and sinks the 5,086-ton Panamanian-flagged merchant JOHNSTOWN at 13-12S, 42-06E.

8 June 1942:
Indian Ocean. The I-20 torpedoes and sinks the 5,209-ton Greek merchant CHRISTOS MARKETTOS at 05-05S, 40-53E.

11 June 1942:
Indian Ocean. The I-20 torpedoes and sinks the 7,926-ton British merchant MAHRONDA at 14-37S, 40-58E.

12 June 1942:
The I-20 shells and sinks the 2,052-ton Panamanian-flagged merchant HELLENIC TRADER at 14-40S, 40-53E.
Later that day, the I-20 torpedoes and sinks the 5,063-ton British merchant CLIFTON HALL at 16-25S, 40-10E.

19 June 1942:
Refuels from the AIKOKU MARU.

29 June 1942:
Indian Ocean. The I-20 torpedoes the 5,063-ton Norwegian merchant GOVIKEN that is en route from Aden to Lourenço Marques, Mozambique. She sinks within 20 minutes at 13-25S, 41-53E.

30 June 1942:
Indian Ocean. The I-20 attacks the 5,311-ton British tanker STEAUA ROMANA at 09S, 42E. First she fires 15 shells from her deck gun, achieving one hit. The STEAUA ROMANA returns fire. Yamada dives and fires a torpedo, that explodes prematurely. The tanker drops a smoke float and tries to open the range but is sunk by a second torpedo.
Later that day, using Allied radio communication intercepts, LtCdr Yamada ascertains his victim's name.

5 July 1942:
In order to discover the cause of his frequent torpedo prematures, Cdr Yamada orders one Type 95 to be dismantled aboard.

21 July 1942:
The I-20 extends her patrol to the Gulf of Aden, then returns to Penang.

5 August 1942:
Arrives at Penang.

14 August 1942:
The I-20 is in Vice Admiral Komatsu Teruhisa's Sixth Fleet (Submarines) at Truk in Subron 1 with the I-15, -16, -17, -18, -19, -21, -22, -24, -25 and the I-26.

On August 23, 1942 arrives Yokosuka for repairs and overhaul. On September 15, 1942 assigned to commander LtCdr Yoshimura Iwao. On October 24, 1942 departs Yokosuka bound for Shortland.

On November 2, 1942 at Shortland I-20 joins I-16 and I-24 to form an attack group under the command of Captain Ota Nobunosuke that will transport a midget submarine from Chiyoda to operate off Guadalcanal. On November 5, 1942 embarks her third midget HA-11 Type A midget submarine and departs Shortland that evening bound for Guadalcanal.

On November 7, 1942 at 5:20am launches HA-11 Type A Midget Submarine four miles north of Cape Esperance off Guadalcanal. Aboard is commander Lt(jg) Nobuharu Kunihiro and and crew member PO1C Goro Inoue. Afterwards, I-20 returns to Truk.

On November 13, 1942 at Truk embarks her fourth midget HA-37 Type A Midget Submarine and departs bound for Guadalcanal. On November 18, 1942 I-20 arrives at her assigned launch area off Guadalcanal. On November 19, 1942 at 3:00am launches HA-37 Type A Midget Submarine under the command of Lt(jg) Miyoshi Yoshiaki with crew member PO1C Umeda Kiyoshi roughly six miles off Guadalcanal but develops a serious oil leak and unable to find targets is scuttled off Cape Esperance.

On November 26, 1942 at Truk embarks her fifth midget HA-8 Type A Midget Submarine and departs bound for Guadalcanal. On December 1, 1942 I-20 arrives in her launch area off Guadalcanal.

On December 2, 1942 at 11:08pm launched HA-8 Type A Midget Submarine roughly 10.8 miles off Cape Esperance on Guadalcanal. The midget submarine is commanded by Lt(jg) Tanaka with crew member Mitani.

On December 18, 1942 assigned to Lt. Cdr Kudo Kaneo.

On December 31, 1942 transports 25 tons of supplies in rubber containers to Cape Esperance on Guadalcanal.

On January 1, 1943 assigned to SubDiv 1, SubRon 8 along with I-16, I-18, I-21 and I-24.


Damaged HMS Ramillies on 09-05-1942 by Kō-hyōteki.
Damaged RMS British Loyalty on 09-05-1942 by Kō-hyōteki.
Sank Panamanian merchant ship Johnstown on 05-06-1942.
Sank Greek merchant vessel Christos Markettos on 08-06-1942.
Sank RMS Mahronda 11-06-1942.
Sank Panamanian merchantman Hellenic Trader on 12-06-1942.
Sank RMS Clifton Hall on 12-06-1942.
Sank Norwegian merchant ship Goviken on 30-06-1942.
Sank RMS Steaua Romana on 30-06-1942.
Damaged unknown merchant ship on 03-12-1942 by Kō-hyōteki.

Sinking History
On November 18, 1943 presumed lost operating off Espiritu Santo. On December 1, 1943 officially removed from the Navy List.

Fates of the Crew
The entire crew is presumed lost with the submarine.

Other sources state this submarine was sunk by USS Ellet off Vella Lavella on October 1, 1943.
Combined Fleet - HIJMS Submarine I-20: Tabular Record of Movement
Combined Fleet - Midget Submarines at Diego Suarez, Madagascar 1942

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Last Updated
November 19, 2021


November 19, 1942
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