Japanese Auxiliary Submarine Tenders

TOKUSETSU SENSUI-BOKAN!

(Chogei by Takeshi Yuki scanned from "Color Paintings of Japanese Warships")

IJN Submarine Tender
RIO DE JANEIRO MARU: Tabular Record of Movement
© 1998-2005 Bob Hackett, Sander Kingsepp and Peter Cundall.
Revision 1

16 May 1929:
Nagasaki. Laid down at Mitsubishi Shipbuilding as a 9,627 GRT passenger-cargo liner for the Osaka Shosen Kaisha (OSK) Line.
19 November 1929:
Launched and named RIO DE JANEIRO MARU.
15 May 1930:
Completed. RIO DE JANEIRO MARU can accomodate 1,140 passengers.
1 June 1930:
Departs her home port of Kobe on her maiden voyage to OSK's South American ports of call.
April 1934:
Runs aground in the Mississippi River estuary.
January 1937:
Provides around-the-world service. Ports of call include Yokohama, Hong Kong, Singapore, Colombo, Durban, Cape Town, Rio de Janeiro, Santos, Montevideo, Buenos Aires, Belem, Cristobal, Balboa and Los Angeles.
8 October 1940:
Requisitioned by the IJN.
19 October 1940:
Kure Navy Yard. Begins conversion to an auxiliary transport.
1 November 1940:
Registered (commissioned) as an auxiliary transport (Unsosen) in the Sasebo Naval District.
30 November 1940:
Completes conversion that includes installation of two 25-mm Type 96 dual AA guns, signal equipment and new accommodation spaces.
24 February 1941:
Departs Sasebo for the South China coast.
3 March 1941:
Arrives at Keelung, Formosa.
25 March 1941:
Registered as an auxiliary submarine depot ship (Sensuibokan) in the Sasebo Naval District.
Banshu, Hyogo. Begins conversion at Harima's shipyard. Four 5.9-inch (150-mm) guns and a range finder are fitted. A torpedo and depth charge hangar is constructed as are replenishment goods storage and a medical facility. Motor launch loading equipment is also installed.
7 May 1941:
Completes conversion.
24 November 1941:
Sasebo. RIO DE JANEIRO MARU is a tender in Rear Admiral (later Vice Admiral), the Marquis, Daigo Tadashige's (former CO of KINU) SubRon 5 with light cruiser YURA (F), SubDiv 28 (I-59, I-60), SubDiv 29 (I-62, I-64) and SubDiv 30 (I-65, I-66).
Departs Sasebo for Palau with YURA and SubDivs 29 and 30. Enroute, SubRon 5 is diverted to Samah, Hainan Island, China.
8 December 1941: Operation "E"- The Invasion of Malaya:
RIO DE JANEIRO MARU arrives at Camranh Bay, Indochina. That same day, Japanese forces land on the Kra Isthmus of Thailand and NE Malaya.
8 January 1942:
Departs Camranh Bay.
10 January 1942:
Arrives at Singora, Malaya and disembarks personnel and equipment of the 11th Submarine Base Unit. Later, steams to Kota Bharu, Malaya, then Brunei, Borneo.
2 April 1942:
Arrives at Sasebo.
10 April 1942:
Sasebo. RIO DE JANEIRO MARU is in SubRon 5 with SubDiv 19 (I-56, I-57, I-58) and SubDiv 30 (I-64, I-65, I-66). SubDiv 28 is deactivated and I-59 is added to Sub Div 19 and I-62 is added to Sub Div 30.
1942:
Kure. Seven coils are fitted all around the ship's side for magnetic mine degaussing.
7 May 1942:
Captain-Retired (later Rear Admiral) Ohashi Tatsuo (40) (former CO of RO-68) assumes command.
14 May 1942: Operation “MI” - The Battle of Midway:
RIO DE JANEIRO MARU is assigned to Vice Admiral, the Marquis, Komatsu Teruhisa’s (former CO of NACHI) Advance (Submarine) Force’s (Sixth Fleet).
RIO DE JANEIRO MARU departs Sasebo for the Dutch East Indies.
29 May 1942:
Balbac Strait, N of Borneo. LtCdr (later Rear Admiral) Chester C. Smith's USS SWORDFISH (SS-193) operating from Fremantle, Australia, is patrolling the Strait. Smith’s lookouts spot a small convoy and he sets up for a submerged night attack. Smith fires two Mark 14 steam torpedoes at a vessel he identifies as a “5,000-ton” oiler. Smith claims no hits, but one of his torpedoes does hit RIO DE JANEIRO MARU and rips open a 46-foot long by 26-foot wide hole in Hold No. 1. [1]
Smith attacks another ship in the convoy. He fires two torpedoes and sinks cargo ship TATSUFUKU MARU.
Later, six sailors volunteer to enter RIO DE JANEIRO MARU's flooded compartment and seal the leak. For their actions they receive a commendation from Admiral Yamamoto Isoroku (former CO of AKAGI), CINC, Combined Fleet.
The repair ships ASAHI MARU and YAMABIKO MARU arrive later and tow RIO DE JANEIRO MARU to Singapore for repairs. [2] [3]
June 1942:
Singapore. RIO DE JANEIRO MARU is drydocked and repaired at Seletar's No. 1 Shipyard (former King George V Graving Dock).
2 July 1942:
Arrives at Sasebo.
10 July 1942:
SubRon 5 is disbanded.
14 July 1942:
Reassigned to Vice Admiral Takahashi Ibo's (former Co of KIRISHIMA) Southwest Area Fleet as a tender for flagship I-8 and SubDiv 30 (I-162, I-165, I-166).
21 July 1942:
Departs Sasebo.
27 July 1942:
94 miles E of Camranh, Indochina. RIO DE JANEIRO MARU is attacked by LtCdr (later Rear Admiral) James C. Dempsey's (former CO of S-37) USS SPEARFISH (SS-190). Dempsey later claims two hits of four torpedoes he fires in a submerged night attack. He departs thinking the stopped ship is sinking by the stern. The next day, Captain Ohashi reports RIO DE JANERIO MARU suffered "medium" damage, but is able to proceed to Hong Kong for repairs.
3 August 1942:
Arrives at Camranh Bay.
27 August 1942:
Replenishes SubDiv 30.
6 October 1942:
Sub Ron 5 is deactivated. RIO DE JANERIO MARU remains with Southwest Area Fleet.
1 January 1943:
Surabaya, Java. Continues service as a tender in the Southwest Area Fleet's SubDiv 30 (1-162, 1-165, 1-166).
25 January 1943:
Employed in transporting air field construction materials to Kokas on the Bay of Sekar, W Java.
12 February 1943:
Ambon, Moluccas. Attacked unsuccessfully by aircraft.
16 March 1943:
Assigned to the Second Southern Expeditionary Fleet of the Southwest Area Fleet.
1 May 1943:
Departs Java for Ambon carrying 200 Allied POWs. [4]
2 July 1943:
Loads drums and cargo for Balikpapan, Borneo. RIO DE JANEIRO MARU is scheduled to carry 5,000 drums of AvGas to Yokosuka.
16 July 1943:
Departs Balikpapan.
23 July 1943:
At Sorong, Vogelkop Peninsula, New Guinea.
27 July 1943:
Arrives at Balikpapan.
1 August 1943:
Departs Balikpapan.
3 August 1943:
Arrives at Surabaya.
23 August 1943:
Arrives at Ambon.
29 August 1943:
Arrives at Surabaya, Java.
30 August 1943:
Departs Surabaya.
31 August 1943:
Arrives at Tarakan.
3 September 1943:
Arrives at Davao, Philippines.
15 September 1943:
Arrives at Manila. That same day, Captain Ohashi is designated the Supervisor of Modification. RIO DE JANEIRO MARU is demilitarized and rerated a civilian transport in the Sasebo Naval District.
Departs Manila for Balikpapan.
2 October 1943:
Departs Makassar, Celebes for Batavia (Jakarta), Java carrying 200 Allied POWs. [4]
4 October 1943:
Arrives at Batavia.
11 October 1943:
Departs Surabaya escorted by minesweeper W-8 until the following day.
22 October 1943:
At 0900, departs Surabaya at 11 knots with fleet oiler KAMOI escorted by minesweeper W-8 as far as the Banka Straits.
25 October 1943:
At 1600, arrives off Horsburgh Light near Singapore.
31 October 1943:
Departs Singapore for Cap St. Jacques, Indochina.
2 November 1943:
Arrives at Cap St. Jacques.
10 November 1943:
Arrives at Takao, Formosa in convoy with NICHIRAN MARU.
14 November 1943:
Departs Takao.
18 November 1943:
Arrives at Sasebo.
24 November 1943:
Departs Sasebo.
26 November 1943:
Arrives at Kure.
29 November 1943:
Departs Kure.
30 November 1943:
Arrives at Osaka.
5 December 1943:
Recalled Captain-Retired Kanemasu Yoshio (former CO of OI) is posted as Supervisor of Modification. Captain Ohashi is reassigned to the Kure Naval District.
14 December 1943:
Departs Osaka. Arrives at the Aioi Shipyard. Begins modifications of a unknown nature, possibly installation of Type 96 25-mm AA machine guns and search radar as carried out at Aioi on other sub tenders.
13 January 1944:
Departs Aioi at 0700 for Miike. Captain Kanemasu is the CO. Completes modifications.
18 January 1944:
Arrives at Kure Naval Arsenal. Loads thousands of rounds of various sizes of ammunition destined for light cruiser AGANO at Truk undergoing repairs by repair ship AKASHI.
23 January 1944:
Departs Kure. Arrives at Kobe.
27 January 1944:
Departs Kobe.
29 January 1944:
Arrives at Yokosuka. Loads a cargo of depth charges, coastal defense guns, foodstuffs and mail for transport.
3 February 1944:
Departs Yokosuka escorted by YUZUKI.
11 February 1944:
Arrives at Truk.
17 February 1944: American Operation "Hailstone" - The Attack on Truk:
Vice Admiral (later Admiral) Marc A. Mitscher’s Task Force 58's five fleet carriers and four light carriers, supported by six battleships, ten cruisers and 28 destroyers, launch air attacks on airfields, shore installations and ships in the lagoon. Mitscher launches 30 strikes of at least 150 aircraft each. Beginning at dawn, the strikes are launched about every hour for two days.
East of Uman Island. The anchored RIO DE JANEIRO MARU is is hit by 1,000-lb. bombs during TF 58's first attacks, probably dropped by SBDs of YORKTOWN (CV-10) and SB2Cs of BUNKER HILL (CV-17). Captain Kanemasu is KIA. He is promoted Rear Admiral, posthumously.
18 February 1944:
At 0030, RIO DE JANEIRO MARU sinks. She comes to rest on her starboard side at depth of 115 feet.
Task Force 58 sinks 31 transports and 10 naval vessels (two cruisers, four destroyers and four auxiliary vessels), destroys nearly 200 aircraft and damages severely about 100 more. Truk is eliminated as a major fleet anchorage for the IJN.
31 March 1944:
Removed from the Navy List.

Authors' Notes:
[1] Noted WWII American submarine researcher Cdr (Ret) John Alden has expressed reservations to the authors about the attack on RIO DE JANEIRO MARU that we attribute to SWORDFISH. Alden further questions the veracity of certain Japanese sources concerning events subsequent to the attack.
[2] Small auxiliary repair ship ASAHI MARU should not be confused with the large hospital ship of the same name (a common Japanese practice) or repair ship (ex-BB) ASAHI sunk a few days earlier off Indochina.
[3] Many books and Orders of Battle (OOB) on the Battle of Midway list RIO DE JANEIRO MARU as being at Kwajalein during the battle. The source of these OOB's is thought by the authors to be Cdr Fuchida Mitsuo and is subject to question.
[4] Because of the conditions Allied POWs had to endure aboard her, RIO DE JANEIRO MARU was considered a "Hell Ship."
Special thanks go to Cdr (Ret) John Alden for his comments.

- Bob Hackett, Sander Kingsepp and Peter Cundall.

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