Japanese Auxiliary Netlayers

KYUSETSUMOKAN!

HOKAKUMOTEI!

(SEIKO MARU – believed sistership of KOKKO MARU)

IJN KOKKO MARU:
Tabular Record of Movement

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

1938:
Osaka. Laid down by Nakata Zosensho K.K. shipyard as a 717-tons cargo ship for Sanko Kisen K.K.
November 1938:
Launched and named KOKKO MARU. [1]
24 December 1938:
Completed and registered at Amagasaki with a Gross Registered Tonnage (GRT) of 717-tons and a Net Registered Tonnage (NRT) of 498-tons. Her call sign is JXFM. [2]
4 March 1939:
Civilian Master Sasanuki Ichiji is appointed CO.
4 September 1941:
Requisitioned by the IJN.
11 September 1941:
Uraga. Conversion for military duty begins at Uraga Senkyo K.K.
12 September 1941:
Registered as an auxiliary netlayer attached to the Yokosuka Naval District under internal instruction No. 1049. Navy (Resv) Lt(jg). Ono Narumi is appointed CO.
13 October 1941:
Conversion for military duty is completed.
15 October 1941:
Attached to 57th Subchaser Division under internal instruction No. 1251. Tactically attached to Vice Admiral Inoue Shigeyoshi’s (37) Fourth Fleet, 4th Base Force, 57th Subchaser Division.
7 November 1941:
Depart Yokosuka for the South Seas (Japanese mandated islands).
11 November 1941:
Rated as auxiliary netlaying boat No. 571.
December 1941:
Attached to the Carolines, Truk Defense Force, Ponape Sea Unit.
1 December 1941:
Heads towards Lamotrek Atoll, Carolines.
5 December 1941:
Departs Lamotrek.
9 December 1941:
Arrives at Truk, Central Carolines.
12 December 1941:
Departs Truk on patrol.
18 December 1941:
Arrives at Truk.
23 December 1941:
Departs Truk on patrol.
27 December 1941:
Arrives at Truk.
28 December 1941:
Departs Truk on patrol.
January ~ April 1942:
Patrols Ponape, Carolines waters.
10 April 1942:
Attached to Ponape Maritime Corps under confidential Truk order No. 10.
23 April 1942:
Attached to Ponape Maritime Corps under confidential Truk order No. 11.
25 April 1942:
Heads towards Ponape.
28 April 1942:
Arrives at Truk.
May 1942 ~ January 1943:
Patrols Ponape waters.
21 January 1943:
Departs Ponape.
23 Janaury 1943:
Arrives at Truk.
27 January 1943:
Departs Truk on patrol outside Truk atoll.
31 January 1943:
Arrives at Truk.
February 1943:
Assigned to the Truk Naval Unit, Northern Unit.
2 February 1943:
Departs Truk patrolling Truk vicinity.
3 February 1943:
Arrives at Truk.
10 February 1943:
Departs Truk patrolling Truk waters.
13 February 1943:
Arrives at Truk.
17 February 1943:
Departs Truk on patrol in Truk vicinity.
21 February 1943:
Arrives at Truk.
25 February 1943:
Departs Truk patrolling Truk waters.
1 March 1943:
Arrives at Truk.
6 March 1943:
Departs Truk on patrol in Truk waters.
7 March 1943:
Arrives at Truk.
21 March 1943:
Departs Truk on patrol in Truk vicinity.
25 March 1943:
Arrives at Truk.
26 March 1943:
Departs Truk patrolling Truk waters.
31 March 1943:
Arrives at Truk.
8 April 1943:
Departs Truk and returns to Base later this day.
11 April 1943:
Departs Truk on patrol in Truk vicinity.
13 April 1943:
Arrives at Truk.
16 April 1943:
Departs Truk and returns there later this day.
21 April 1943:
Departs Truk on patrol in Truk vicinity.
23 April 1943:
Arrives at Truk.
25 April 1943:
Departs Truk on patrol in Truk vicinity.
26 April 1943:
Arrives at Truk.
3 May 1943:
Departs Truk patrolling Truk waters.
5 May 1943:
Arrives at Truk.
7 May 1943:
Departs Truk on patrol in Truk vicinity.
8 May 1943:
Arrives at Truk.
10 May 1943:
Departs Truk on an escort mission for Endabi (Puluwat), Carolines.
12 May 1943:
Departs Endabi.
13 May 1943:
Arrives at Truk.
15 May 1943:
Departs Truk on patrol in Truk vicinity.
18 May 1943:
Arrives at Truk.
20 May 1943:
Departs Truk patrolling Truk waters.
24 May 1943:
Arrives at Truk.
9 June 1943:
Departs Truk on patrol in Truk vicinity.
11 June 1943:
Arrives at Truk.
13 June 1943:
Departs Truk patrolling Truk waters.
17 June 1943:
Arrives at Truk.
20 June 1943:
Departs Truk for Mortlock (Nomoi), Carolines.
22 June 1943:
Departs Mortlock and calls at Greenwich (Kapingamarangi), Eastern Carolines. Departs there later this day.
23 June 1943:
Arrives at Truk.
26 June 1943:
Departs Truk.
28 June 1943:
Arrives at Lamotrek and departs there later that day.
29 June 1943:
Departs Mereyon, Carolines.
July 1943:
Attached to the Truk Maritime Patrol Corps under confidential Carolines Front Defense Force order No. 22.
3 July 1943:
Arrives at Lamotrek and departs there later this day.
4 July 1943:
Arrives at Truk. Undergoes engine, generator and anchor repairs.
5 August 1943:
Repairs are completed.
6 August 1943:
Departs Truk patrolling Truk waters and afterwards on escort mission.
13 August 1943:
Arrives at Truk.
23 August 1943:
Departs Truk on patrol in Truk vicinity.
28 August 1943:
Arrives at Truk.
1 September 1943:
Departs Truk on an anti-submarine sweep.
11 September 1943:
Arrives at Truk.
15 September 1943:
Departs Truk patrolling Truk waters.
20 September 1943:
Arrives at Truk.
21 September 1943:
Departs Truk on a rescue mission and afterwards on escort mission.
25 September 1943:
Arrives at Truk.
6 October 1943:
Departs Truk on patrol in Truk vicinity.
9 October 1943:
Arrives at Truk.
11 October 1943:
Departs Truk patrolling Truk waters.
12 October 1943:
Navy Lt. (Resv) Zushi Masafuni is appointed CO.
15 October 1943:
Arrives at Truk.
21 October 1943:
Departs Truk on a gunnery exercise and returns to base later that day.
25 October 1943:
Departs Truk on an anti-submarine sweep.
27 October 1943:
Arrives at Truk.
E 28 October ~ 28 November 1943:
Undergoes repairs.
29 November 1943:
Departs Truk patrolling Truk waters and then escorts a fishing boat.
5 December 1943:
Arrives at Truk.
9 December 1943:
At 0700, departs Truk.
10 December 1943:
At 1000, arrives at Mortlock.
11 December 1943:
Departs Mortlock.
13 December 1943:
Arrives at Truk.
25 December 1943:
Departs Truk on patrol in Truk vicinity and then on escort mission. [3]
28 December 1943:
At 1200, together with auxiliary minesweeper Wa-6 scheduled to meet up with convoy No. 1210 consisting of auxiliary stores ships CHIYO, HOKO, SHINYO and TAIYO MARUs escorted by auxiliry minesweeper FUMI MARU No. 2 and auxiliary subchaser KYO MARU No. 8 and replace FUMI MARU No. 2 and KYO MARU No. 8 as escorts. FUMI MARU No. 2 and KYO MARU No. 8 will return to Saipan, Marianas. [3]
29 December 1943:
At 1217, the convoy reports a torpedo attack in 07-57N, 147-46E but sustains no damage.
30 December 1943:
The convoy is scheduled to arrive at 1530, at Truk South Channel.
1 January 1944:
Arrives at Truk.
4 January 1944:
Departs Truk on patrol in Truk vicinity.
6 January 1944:
Arrives at Truk.
10 January 1944:
Departs Truk on patrol in ‘LC’ area.
15 January 1944:
Arrives at Truk.
19 January 1944:
Departs Truk on an anti-submarine sweep in ‘NA’ area and escorts with kaibokan AMAKUSA, auxiliary subchaser CHa-23, auxiliary minesweeper NOSHIRO MARU No. 2 GO and auxiliary gunboat CHOAN MARU No. 2 departing convoy No. 4119 consisting of Navy storeship KINEZAKI, IJN requisitioned cargo ship (B-AK) TATEBE (KEMBU) MARU and civilian cargo ship (C-AK) HOKOKU MARU and auxiliary collier/oiler MIKAGE MARU No. 18 and one unidentified MARU. [4]
20 January 1944:
At 0900, with auxiliary minesweeper NOSHIRO MARU No. 2 GO detaches from the convoy.
23 January 1944:
At 0441, with auxiliary minesweeper NOSHIRO MARU No. 2 GO meets up with convoy No. 3109 (previously called convoy No. 3107) consisting of KOSHIN (6530 grt) and GOSEI MARUs escorted by kaibokan FUKUE.
27 January 1944:
Arrives at Truk.
28 January 1944:
Departs Truk on an anti-submarine sweep.
6 February 1944:
Arrives at Truk.
15 February 1944:
Departs Truk on patrol in Truk vicinity and then on anti-submarine sweep.
19 February 1944:
Arrives at Truk.
22 February 1944:
Departs Truk for Mortlock.
26 February 1944:
Arrives at Truk.
29 February 1944:
Departs Truk for Ponape.
4 March 1944:
Attached to Vice Admiral Nagumo Chuichi’s (36) Central Pacific Area Fleet, Fourth Fleet, 4th Base Force, 57th Subchaser Division.
6 March 1944:
Arrives at Truk.
10 March 1944:
Departs Truk for Lamotrek.
13 March 1944:
Arrives at Truk.
14 March 1944:
Departs Truk for Lamotrek.
18 March 1944:
Arrives at Endabi.
19 March 1944:
Departs Endabi.
22 March 1944:
Arrives at Truk. Undergoes repairs.
31 March 1944:
Attached to 57th Subchaser Division under internal order No. 503.
6 April 1944:
Departs Truk.
9 April 1944:
Arrives at Mereyon.
10 April 1944:
Departs Mereyon and arrives at Lamotrek later this day.
11 April 1944:
Departs Lamotrek.
13 April 1944:
Arrives at Truk.
23 April 1944:
Departs Truk.
24 April 1944:
Arrives at Mortlock.
25 April 1944:
Departs Mortlock.
26 April 1944:
Arrives at Truk. Later this month reclassified as a Patrol Unit under confidential Caroline Area Defense order No. 14.
13 May 1944:
KOKKO MARU is reported as sailing westward from Yokosuka, alone, at 8 knots. .
11 June 1944:
Saipan. Fear of an imminent Allied invasion causes all navigable ships to flee. At 0400, KOKKO MARU departs Saipan for Tokyo Bay with kaibokan CD-4, torpedo boat OTORI, subchasers CH-33, CH-50 and CH-51, auxiliary subchasers CHa-20 and CHa-50 and TAKUNAN MARU No. 8 and auxiliary minesweeper Wa-6 escorting convoy No. 4611 consisting of IJA transport FUKOKU MARU and IJN transports BATAVIA, HINKO, SHINTO (KAMISHIMA), IMIZU, NITCHO, REIKAI, TENRYUGAWA, KEIYO, BOKUYO (MUTSUYO), MOJI, MAMIYA, INARI and TATSUTAKAWA MARUs and 16 other unidentified ships.
12 June 1944: American Operation “Forager” – The Invasion of Saipan:
Vice Admiral (later Admiral) Richmond K. Turner’s (USNA ’08) Task Force 52 lands Marine LtGen Holland M. Smith’s V Amphibious Corps and the invasion of Saipan begins. Vice Admiral (later Admiral) Marc A. Mitscher’s (USNA ’10) Task Force 58 launches aircraft from 15 carriers to attack airfields, defenses and shipping in the Marianas.
At 0935, that same day, at 17-32N, 144-10E, TG 58.4’s carriers USS ESSEX (CV-9), USS LANGLEY (CVL-27) and USS COWPENS (CVL- 25) find and decimate convoy No. 4611.
They sink torpedo boat OTORI, and BATAVIA (59 crewmen and 18 passengers KIA), HINKO (actually sank after air attack 25 June and submarine attack 19 July nine crewmen and 12 passengers KIA including those KIA when sunk later in month by air attack), SHINTO (KAMISHIMA) (53 crewmen and 54 passengers KIA), IMIZU (67 crewmen KIA), NITCHO (14 crewmen KIA), REIKAI (40 crewmen and 42 passengers KIA), TENRYUGAWA (seven crewmen KIA), BOKUYO (45 crewmen KIA), FUKOKU (51 crewmen and 31 passengers KIA) and MOJI (53 crewmen and five gunners KIA) MARUs and damage TATSUTAKAWA MARU, CD-4, CH-33, CH-50 and CH-51, CHa-20 and Wa-6.
TATSUTAKAWA MARU is left drifting and is finished off by gunfire of US destroyers BOYD (DD-544) and CHARRETTE (DD-581) three days later. 15 crewmen and two passengers are KIA. MAMIYA MARU is detached and sunk three days later by USN carrier based aircraft near Iwo Jima with the loss of seven of her crew.
Task Force 58’s planes also sink KOKKO MARU at 17-32N, 144-10E, about 100 nautical miles W Alamagan Island, Marianas. Two crewmen are KIA.
10 August 1944:
Removed from the Navy’s list under internal instruction No. 949.

Authors' Notes:
[1] Not to be confused with ore carrier (5,486 GRT. ’42).
[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] The 901 air Kokutai reports on 27 December that it provided air cover for a convoy consisting of six ships that departed Saipan probably late on 26 December 1944. The convoy likely consisted of CHIYO, HOKO and TAIYO MARUs and three unidentified vessels. Depending whether or not escorts are included in this total number, these unidentified vessels could be auxiliary stores ship SHINYO MARU with escorts auxiliary minesweeper FUMI MARU No. 2 and auxiliary subchaser KYO MARU No. 8 or SHINYO MARU and IJA auxiliary transport MOMOKAWA MARU and one unidentified vessel. SHINYO MARU supposedly departed Saipan at 1300 on 26 December and arrives 0715 at Truk on 31 December 1944. MOMOKAWA MARU supposedly departed Saipan at 27 December 1944 escorted by minelayer NASAMI and arrives at Truk on 31 December 1944. Authors assume escorts were included in the report about the six ship convoy.
[4] Auxiliary subchaser CHa-23 and auxiliary gunboat CHOAN MARU No. 2 may only have proceeded as far as Chichi-Jima.
Thanks go to Gengoro S. Toda of Japan.

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

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