Japanese Auxiliary Netlayers

KYUSETSUMOKAN!

HOKAKUMOTEI!

(KOSEI MARU, sister of KOEI MARU, prewar)

IJN KOEI MARU:
Tabular Record of Movement

© 2022 Gilbert Casse, Berend van der Wal and Peter Cundall

1941:
Osaka. Laid down by Amagasaki Dock K.K. as a 863-tons cargo ship for Amakasu Sangyo Kisen K.K.
29 May 1941:
Launched and named KOEI MARU. [1]
20 September 1941:
Completed and registered at Yokohama, with a Gross Registered Tonnage (GRT) of 863-tons and a Net Registered Tonnage (NRT) of 601-tons. Her call sign is JKAO. [2]
10 November 1941:
Requisitioned by the IJN.
1 December 1941:
Registered as an auxiliary netlayer attached to the Yokosuka Naval District under Cabinet Order No. 1571. Navy (Resv) Lt. Asano Ikuo is appointed CO.
10 December 1941:
Conversion for military duty is completed at Tokyo Ishikawajima Zosensho K.K. Attached to 58th Subchaser Division under instruction No. 1619. Attached to Vice Admiral (later Admiral) Inoue Shigeyoshi’s (37) Fourth Fleet in Vice Admiral Moizumi’s (37) 4th Base Force based at Truk, Central Carolines, 58th Subchaser Division.
E10 ~ 30 December 1941:
Attached to Truk Naval Force under Truk Direction Defense Unit Command order No. 8.
30 December 1941:
Departs Yokosuka.
8 January 1942:
Arrives at Truk.
11 January 1942:
Departs Truk on patrol in TA-1 area.
13 January 1942:
Arrives at Truk.
14 January 1942:
Departs Truk on patrol in TA-1 area.
15 January 1942:
Arrives at Truk.
17 January 1942:
Departs Truk on patrol in KA-1 area.
22 January 1942:
Arrives at Truk.
23 January 1942:
Departs Truk on patrol in KA-1 and TA-1 areas.
28 January 1942:
Arrives at Truk.
29 January 1942:
Rated as netlayer No. 581 (ship No. 1 in 58th Subchaser Division).
2 February 1942:
Departs Truk on patrol in KA-1 area.
5 February 1942:
Arrives at Truk.
8 February 1942:
Departs Truk on patrol in KA-1 area.
12 February 1942:
Arrives at Truk.
15 February 1942:
Departs Truk on patrol in KA-1 area.
18 February 1942:
Arrives at Truk.
19 February 1942:
Departs Truk on patrol in TA-3 area.
21 February 1942:
Arrives at Truk.
23 February 1942:
Departs Truk on patrol in KA-1 area.
3 March 1942:
Arrives at Truk.
6 March 1942:
Departs Truk on patrol in KA-1 area.
9 March 1942:
Arrives at Truk.
12 March 1942:
Departs Truk on patrol in LI-1 area.
15 March 1942:
Arrives at Truk.
18 March 1942:
Departs Truk on an anti-submarine patrol in Kuop (Neoch) Atoll, Carolines.
21 March 1942:
Arrives at Truk.
22 March 1942:
Departs Truk on patrol in KA-1 area.
28 March 1942:
Arrives at Truk.
2 April 1942:
Departs Truk on patrol in TA-1 area.
7 April 1942:
Arrives at Truk.
10 April 1942:
Attached to Truk Naval Corps under Truk Direction Defense Unit Command instruction No. 10.
14 April 1942:
Departs Truk on an anti-submarine patrol.
16 April 1942:
Arrives at Truk.
22 April 1942:
Departs Truk on patrol in TA-1 area.
23 April 1942:
Attached to Truk Naval Corps under Truk Direction Defense Unit Command instruction No. 11.
27 April 1942:
Arrives at Truk.
3 May 1942:
Departs Truk on patrol in TA-1 patrol area.
4 May 1942:
Auxiliary merchant cruiser KINJOSAN MARU heading for Truk, sinks after being torpedoed by LtCdr (later Rear Admiral) Henry C. Bruton’s (USNA '26) USS GREENLING (SS-213).
6 May 1942:
Departs area TA-1 searching for missing auxiliary merchant cruiser KINJOSAN MARU. [3]
7 May 1942:
Arrives at Truk.
11 May 1942:
Departs Truk on gunnery training and returns to base later this day.
12 May 1942:
Departs Truk on patrol in KA-1 area.
16 May 1942:
Auxiliary transport GOYO MARU is heavily damaged S Truk after being torpedoed by LtCdr (later Cdr) Joseph H. Willingham’s (USNA ’26) USS TAUTOG (SS-199). Ship is beached on Royalist Reef off Truk to prevent sinking.
18 May 1942:
Departs area KA-1 searching for auxiliary transport GOYO MARU.
19 May 1942:
Auxiliary gunboats HEIJO MARU and CHOAN MARU No. 2 GO commence towing GOYO MARU.
23 May 1942:
Engages in anti-submarine sweeping and then patrols area KA-1.
27 May 1942:
Arrives at Truk.
1 June 1942:
Departs Truk on an anti-submarine sweep and then patrols area TA-1.
6 June 1942:
Arrives at Truk.
20 June 1942:
Departs Truk on an anti-submarine sweep.
24 June 1942:
Arrives at Truk.
1 July 1942:
Departs Truk on an anti-submarine sweep.
4 July 1942:
Arrives at Truk.
7 July 1942:
Departs Truk on escort mission and then patrols area TA-1.
14 July 1942:
Arrives at Truk.
21 July 1942:
Departs Truk on an anti-submarine sweep.
26 July 1942:
Arrives at Truk.
29 July 1942:
Departs Truk on an anti-submarine sweep.
5 August 1942:
Arrives at Truk. That same day, auxiliary transport BRASIL MARU sinks NW Truk after being torpedoed by LtCdr (later Rear Admiral) Henry C. Bruton’s (USNA ’26) USS GREENLING (SS-213).
13 August 1942:
Departs Truk on an anti-submarine sweep.
15 August 1942:
Ends anti-submarine sweeping and starts searching for survivors of sunken auxiliary transport BRASIL MARU. [4]
17 August 1942:
Patrols patrol area KA-1.
20 August 1942:
Arrives at Truk.
22 August 1942:
Departs Truk on an anti-submarine sweep and then escort mission.
24 August 1942:
Arrives at Truk.
27 August 1942:
Departs Truk on an anti-submarine sweep.
29 August 1942:
Arrives at Truk. Departs on an anti-submarine sweep later that day.
21 September 1942:
LtCdr (later Vice Admiral/MOH/COMSUBLANT) Lawson P. Ramage's (USNA ’31) USS TROUT (SS-202) torpedoes and sinks KOEI MARU with 3 torpedoes at 06-54N, 151-51E, about 22 nautical miles of S Passage, Truk. 23 ship gunners are KIA.
20 October 1942:
Detached from 58th Subchaser Division under instruction No. 1936. Removed that same day from the Navy’s list under instruction No. 1938.

Authors' Notes:
[1] Not to be confused with auxiliary minelayer (6,774 GRT, ’34) or IJA shared oiler (Std. 2TL Type - (A/C-AO) No. 5175) - (10,238 GRT, ’44).
[2] NRT is a ship's cargo volume capacity expressed in "register tons", one of which equals to a volume of 100 cubic feet (2.83 m3). It is calculated by subtracting non-revenue-earning spaces i.e. spaces not available for carrying cargo, for example engine rooms, fuel tanks and crew quarters, from the ship's gross register tonnage (GRT). Net register tonnage (NRT) is not a measure of the weight of the ship or its cargo, and should not be confused with terms such as deadweight tonnage or displacement.
[3] Auxiliary repair ship YAMASHIMO MARU rescues three survivors on 13 May ’42.
[4] 212 survivors were rescued by other ships.
Thanks go to Gengoro S. Toda of Japan.

- Gilbert Casse, Berend van der Wal and Peter Cundall.

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