Japanese Oilers

YUSOSEN!

(HOZAN MARU sistership of UNKAI MARU No. 5, in wartime)
IJN UNKAI MARU No. 5:
Tabular Record of Movement
© 2016 Berend van der Wal, Gilbert Casse and Peter Cundall
Revision 3

E 1942:
Osaka. Laid down by Osaka Zosensho K.K. shipyard for Nakamura Kisen K.K. as a Standard Peacetime (C) Type 2,841 GRT cargo ship.
10 December 1942:
Scheduled to be requisitioned from 13 December 1942 under Third Secret Military Preparation instructions.
February 1943:
Completed and named UNKAI MARU No. 5. [1]
March 1943:
Completed and registered at Kobe.
31 March 1943:
Registered as a general transport (refueling ship), attached to the Kure Naval District.
1 April ~ 13 April 1943:
Conversion begins to an oil tanker (primary emergency oil tanker).
14 April 1943:
The conversion is completed. Departs Osaka.
14 April ~ 28 May 1943:
Calls at Kure, Dairen, Sasebo and Tokuyama.
15 May 1943:
Due to depart Tokuyama.
29 May 1943:
Arrives at Takao, Formosa (now Kaoshiung, Taiwan).
30 May 1943:
Departs Takao.
10 June 1943:
At 0900, departs in unescorted convoy No. 585 also consisting of transports NICHIRAN, TACOMA, MYOGI and MANSHU MARUs, tankers SHOYO and PALEMBANG MARUs. UNKAI MARU No. 5 is towing No. 23 special tanker.
13 June 1943:
Arrives at Singapore.
16 June 1943:
Departs Singapore .
E 17 June ~ 30 August 1943:
Makes 7 journeys from Singapore to Palembang and back.
17 June 1943:
Arrives at Palembang, Sumatra.
21 June 1943:
Departs Palembang.
24 June 1943:
At 0700, arrives at Singapore.
E 26 June 1943:
Departs Singapore.
28 June 1943:
At 1820, arrives at Palembang.
29 June 1943:
Departs Palembang.
9 July 1943:
Departs Palembang.
17 July 1943:
At 0900, due to depart Singapore with NASUSAN MARU.
18 July 1943:
At 1300, due to arrive at Moesi (Musi) Rivermouth, Sumatra.
23 August 1943:
A message is sent advising the ship will be derequisitioned from 27 August 1943. (New charter planned from 31 August 1943).
30 August 1943:
Arrives at Singapore.
4 November 1943:
Arrives Singapore probably from Palembang.
9 November 1943:
Departs Palembang.
16 November 1943:
At 2130, arrives at Palembang.
21 November 1943:
Derequisitioned and requisitionend again as a Navy supply ship attached to the Kure Naval District.
8 December 1943:
Scheduled to be registered as a Navy supply ship under Third Secret Military Preparation instruction No. 422.
12 December 1943:
Designated the 19th special Naval ship.
12 January 1944:
At 2000, arrives at Palembang.
30 January 1944:
Departs Palembang with CHORAN MARU.
1 February 1944:
Arrives at Singapore.
20 February 1944:
Scheduled to be registered as a Navy supply ship under Third Secret Military Preparation instruction No. 216.
29 February 1944:
Departs Palembang but returns back to port.
1 March 1944:
Departs Palembang with tanker KAIKO MARU.
3 March 1944:
Arrives at Singapore.
5 March 1944:
Departs Singapore.
6 March 1944:
Arrives at Palembang.
7 March 1944:
Departs Palembang.
9 March 1944:
Arrives at Singapore.
11 March 1944:
Departs Singapore.
12 March 1944:
Arrives at Palembang.
13 March 1944:
Departs Palembang.
15 March 1944:
Arrives at Singapore.
18 March 1944:
Departs Singapore.
19 March 1944:
Arrives at Palembang.
20 March 1944:
Departs Palembang.
22 March 1944:
Arrives at Lingga, off the east coast of Sumatra.
23 March 1944:
Departs Lingga.
24 March 1944:
Arrives at Palembang.
25 March 1944:
Departs Palembang.
26 March 1944:
Arrives at Lingga.
27 March 1944:
Departs Lingga.
28 March 1944:
Arrives at Palembang.
29 March 1944:
Departs Palembang.
30 March 1944:
Arrives at Lingga.
1 April 1944:
Departs Lingga.
2 April 1944:
Arrives at Palembang.
3 April 1944:
Departs Palembang.
4 April 1944:
Arrives at Lingga.
9 April 1944:
Departs Lingga.
10 April 1944:
Arrives at Palembang.
11 April 1944:
Departs Palembang.
12 April 1944:
Arrives at Lingga.
16 April 1944:
Departs Lingga.
17 April 1944:
Arrives at Palembang.
20 April 1944:
Departs Palembang.
21 April 1944:
Arrives at Lingga.
23 April 1944:
Departs Lingga.
24 April 1944:
Arrives at Palembang.
25 April 1944:
Departs Palembang.
26 April 1944:
Arrives at Lingga.
27 April 1944:
Departs Lingga.
28 April 1944:
Arrives at Palembang.
30 April 1944:
Departs Palembang.
1 May 1944:
Arrives at Lingga.
2 May 1944:
Departs Lingga.
3 May 1944:
Arrives at Palembang.
4 May 1944:
Departs Palembang.
5 May 1944:
Arrives at Lingga.
8 May 1944:
Departs Lingga and later that day arrives at Singapore.
11 May 1944:
Departs Singapore.
17 May 1944:
Arrives at Pangkalan Susu, Sumatra.
18 May 1944:
Departs Pangkalan Susu and later that day arrives at Aroa Islands, Malacca Straits.
19 May 1944:
Departs Aroa Islands.
20 May 1944:
Arrives at Singapore.
29 May 1944:
Departs Singapore.
31 May 1944:
Arrives at Palembang.
1 June 1944:
Departs Palembang.
3 June 1944:
Arrives at Singapore.
5 June 1944:
Departs Singapore.
7 June 1944:
Arrives at Palembang.
8 June 1944:
Departs Palembang.
10 June 1944:
Arrives at Singapore.
12 June 1944:
Departs Singapore.
14 June 1944:
Arrives at Palembang.
15 June 1944:
Departs Palembang.
17 June 1944:
Arrives at Singapore.
20 June 1944:
At 1000, departs Singapore in convoy SHIMI-04 also consisting of MATSUMOTO, NANSEI, NICHINAN (5175 grt), NICHINAN (1945 grt), KOTOKU, ZUIHO MARUs and OGURA MARU No. 2 escorted by minesweeper W-18, auxiliary minesweepers TOSHI MARU and CHOUN MARU No. 6.
21 June 1944:
Scheduled to be registered as a Navy supply ship under Third Secret Military Preparation instruction No. 558.
24 June 1944:
At 1100, arrives at Miri, Borneo.
27 June 1944:
At 1650, departs Miri in convoy MI-06 consisting also of tankers OGURA MARU No. 2, YAMAMIZU MARU No. 2, KOTOKU, MATSUMOTO, TACHIBANA, TOKUWA, CERAM, NANSEI, ATAGO, NICHINAN (1945 grt), NICHINAN (5175 grt), ZUIHO and BAIEI MARUs escorted by kaibokan CD-14, patrol boat PB-38 and minesweeper W-18.
E 1 July 1944:
At 1140, W-18 responds to an alarm and drops three depth charges. Later that day, W-18 is detached from the convoy.
2 July 1944:
At 0845, arrives at Manila. While entering port CERAM MARU collides with NANSEI MARU and is run aground to prevent sinking.
4 July 1944:
At 1145, departs Manila in convoy now consisting consisting of tankers ATAGO, TACHIBANA, TOKUWA, MATSUMOTO and ZUIHO MARUs, UNKAI MARU No. 5, YAMAMIZU MARU No. 2 and OGURA MARU No. 2 and transports TSUYAMA, AKAGISAN, KANKYO, YAGI and ATSUTA MARUs escorted by kaibokan CD-14, patrol boat PB-38 and minesweeper W-18.
10 July 1944:
At 1445, arrives at Takao. CD-8 and patrol boat TAKUNAN MARU No. 3 join the convoy. RIKKO, GENKAI, IWATO, JUKO, AOBASAN and HIROTA MARUs also join the convoy.
11 July 1944:
At 2000, W-18 transfers to Saei.
12 July 1944:
At 0254, the convoy departs Takao. At 0330, W-18 departs Saei and joins the convoy.
17 July 1944:
At 1450, arrives at Moji. Later that day arrives at Tokuyama.
25 July 1944:
Departs Tokuyama.
26 July 1944:
Arrives at Osaka. Enters drydock.
11 August 1944:
Departs Osaka.
12 August 1944:
Arrives at Tokuyama.
16 August 1944:
Departs Tokuyama and later that same day arrives at Hesaki.
17 August 1944:
Departs Hesaki and later that same day arrives at Moji.
18 August 1944:
Departs Moji and later that day arrives at Mutsure.
19 August 1944:
Departs Mutsure in convoy MI-15 also consisting of URATO, EKKAI, HOKUSEN, TSINGTAO, TOSHIKAWA, RIKKO, TAISHO, NANSEI and CHIYODA MARUs with OKINOYAMA MARU No. 5, escorted by minelayer SHIRATAKA, minesweeper W-21, and destroyers WAKABA, HATSUHARU and HIBIKI.
25 August 1944:
At 1600, arrives at Takao.
30 August 1944:
At 1500, departs Takao for Manila in reorganized convoy MI-15 that now also consists of RIKKO, TAISHO, OKUNI (TAIKOKU), EIKYU, auxiliary storeship SHINYO, NANSEI, HOSEN and CHIYODA MARUs with OKINOYAMA MARU No. 5 and KYOEI MARU No. 10, escorted by minelayer SHIRATAKA, minesweeper W-21, and kaibokan CD-10 and CD-20.
31 August 1944:
Luzon Strait, S of Formosa. At about 0220, LtCdr (later Rear Admiral) Charles E. Loughlin's (USNA ’33) USS QUEENFISH (SS-393) hits CHIYODA MARU with four torpedoes and sets her afire. At 0240, as the moon sets, CHIYODA MARU sinks. She was carrying 430 passengers, coal briquettes and drummed gasoline. 382 passengers and 15 of the crew are KIA. Loughlin also damages oiler RIKKO MARU steaming in ballast but carrying 506 men of the 3rd Aviation Army, 5th Aviation Communication Unit, boy soldiers and others.
LtCdr (later Vice Admiral) Eli T. Reich's (USNA ’35) USS SEALION (SS-315), a member of "Ben's Busters" with USS GROWLER (SS-215) and USS PAMPANITO, enters the Bashi Strait. USS SEALION’s SJ radar picks up the convoy and Reich makes a night surface approach. He sets up and fires six torpedoes, but they all run erratically. About 0500, Reich swings USS SEALION and fires his four stern torpedoes at a large tanker. He claims two hits. About the same time, Oakley’s USS GROWLER makes a night surface radar attack and fires three torpedoes at a large tanker, probably RIKKO MARU. Oakley also claims two hits.
RIKKO MARU is hit by three torpedoes at 21-30N, 121-19E. 117 passengers and eight crewmen are KIA. The ship is enveloped in black smoke with only the stern visible, but does not sink, possibly indicating one or more of the torpedoes were duds.
Alerted by code-breaker's "Ultra" signals, LtCdr (later Rear Admiral) Eugene B. Fluckey's (USNA ’35) USS BARB (SS-220) intercepts the convoy. At about 0700, Fluckey torpedoes OKUNI MARU. She sinks stern first with three of her crewmen dead. Fluckey also sinks the 45th Minesweeper Squadron's HINODE MARU No. 20 that was patrolling in the area. Two crewmen are KIA.
USS SEALION evades the convoy's escorts. Still surfaced, LtCdr Reich makes an “end-around” approach and works his way ahead of the convoy. At 0715 (JST), SHIRATAKA's lookouts spot a submarine on the surface at 21-05N, 121-26E. Reich misidentifies SHIRATAKA as a destroyer. He begins a submerged approach. At 0730, Reich hits SHIRATAKA with two of three torpedoes. At 1115, SHIRATAKA sinks at 20-55N, 121-07E. Captain Miki Takahide (46) is KIA. He is promoted Rear Admiral, posthumously.
1 September 1944:
RIKKO MARU arrives at Takao, probably under tow. At 2120, CD-20 arrives at Tungchiang escorting NANSEI and TAISHO MARUs.
2 September 1944:
At 2355, the convoy departs (less TAISHO MARU that returns to Takao).
5 September 1944:
At 1900, arrives at North San Fernando, Philippines.
6 September 1944:
At 0800, departs North San Fernando.
7 September 1944:
At 1000, the remainder of convoy MI-15 arrives at Manila.
8 September 1944:
Departs Manila.
10 September 1944:
Arrives at Subic Bay, Philippines.
12 September 1944:
Departs Subic Bay.
14 September 1944:
At 0500, convoy MI-17 consisting of SORACHI, SHIMOTSU, NICHIZUI, HOSEN, TAISHO MARUs, SHINYO MARU No. 8, UNKAI MARU No. 5 and KYOEI MARU No. 10 and four unidentified merchant ships escorted by destroyers SHIOKAZE and KURETAKE and minesweeper W-41 leaves Manila because of an anticipated air attack and arrives that evening at Santa Cruz.
15 September 1944:
Departs Santa Cruz, Philippines, and that evening arrives at Masinloc, Philippines.
16 September 1944:
Departs Masinloc.
22 September 1944:
At 0800, departs Singapore in convoy MI-18 consisting of HIYORI, KIKUSUI, RYOFU, HIGANE, KAISOKU and KOKUSEI MARUs escorted by destroyer SHIOKAZE and second class destroyer KURETAKE.
26 September 1944:
Arrives at Miri. The convoy loads cargo. NANSHIN MARU No. 18, that departed Singapore unescorted on 22 September, arrives and joins the convoy.
30 September 1944:
At 0630, the convoy departs Miri.
2 October 1944:
Off Gaya Bay, NW Borneo. At 0030, LtCdr John C. Martin's (USNA ’34) USS HAMMERHEAD (SS-364) attacks the convoy. Martin torpedoes and sinks bauxite ore-carriers HIYORI (four passengers, three escort troops and 27 crewmen KIA), HIGANE transporting in addition of her cargo of bauxite, 36 passengers, trucks and drummed gasoline (seven passengers, two escort troops and six crewmen KIA) and KOKUSEI (31 troops who were passengers on board, one gunner and 15 crewmen KIA) MARUs. The destroyers do not counter-attack. The convoy immediately shelters in Gaya Bay.
3 October 1944:
At 0530, departs Gaya Bay. At 1900, arrives at Kudat, north Borneo.
4 October 1944:
At 0630, departs Kudat and at 1900; arrives at Balabac, Philippines.
5 October 1944:
At 0600, departs Balabac and at 1830, arrives at Eran Bay, Palawan, Philippines.
6 October 1944:
At 0600, departs Eran Bay and at 2000, arrives at St Pauls Bay, Palawan, Philippines.
7 October 1944:
At 0900, departs St Pauls Bay.
8 October 1944:
At 1900, arrives at Lubang, Philippines.
9 October 1944:
At 0700, departs Lubang.
10 October 1944:
At 2308, arrives at Manila.
11 October 1944:
Departs Manila still in convoy MI-18, to seek refuge from anticipated air raids.
13 October 1944:
At 2200, arrives at Bacuit Bay, Palawan, Philippines where the convoy is dissolved.
22 October 1944:
Departs Manila.
24 October 1944:
Arrives at Ulugan Bay, Palawan, Philippines.
25 October 1944:
Departs Ulugan Bay.
26 October 1944:
Arrives at Calandorang Bay, Palawan, Philippines.
27 October 1944:
Departs Calandorang Bay.
29 October 1944:
Arrives at Tarakan, Borneo.
31 October 1944:
Departs Tarakan and later that day arrives at Tawau, British Borneo.
1 November 1944:
Departs Tawau and arrives at Sandakan, British Borneo, before departing later that day.
7 November 1944:
Arrives at Manila.
12 November 1944:
Departs Manila in convoy MATA-32 that consists also of NANKING MARU and fleet supply ship KURASAKI escorted by second class destroyer KURETAKE and kaibokan CD-1, CD-3 and CD-7.
14 November 1944:
At 2218, LtCdr William T. Kinsella’s (USNA ‘34) USS RAY (SS-271) torpedoes and sinks CD-7 with 165 crewmen lost at 17-46N, 117-57E, off Cape Bolinao, Luzon, Philippines.
At 2225, LtCdr Maurice W. Shea’s (USNA ‘37) USS RATON (SS-270) torpedoes and sinks UNKAI MARU No. 5 about 162 nautical miles W of Vigan, Luzon, Philippines at 17-49N, 117-58E. 43 crewmen are KIA.

Author’s notes:
[1] Not to be confused with IJA transport No. 166 (3,330 GRT, ’00).
Thanks go to Gengoro S. Toda of Japan.
- Berend van der Wal, Gilbert Casse and Peter Cundall.

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