Japanese Auxiliary Netlayers

KYUSETSUMOKAN!

HOKAKUMOTEI!
(SEIKO MARU Plan, Peter Cundall’s Collection)

IJN SEIKO MARU:
Tabular Record of Movement

© 2024 Gilbert Casse, Berend van der Wal and Peter Cundall

E 1938:
Osaka. Laid down by Endo Zosen Tetsu Kosho as a 708-tons cargo ship for Sanko Kisen K.K.
July 1938:
Launched and named SEIKO MARU.[1]
. 26 September 1938:
Completed and registered at Amagasaki. Her gross registered (GRT) tonnage and net registered tonnage (NRT) respectively are 708-tons and 511-tons. Her call sign is JQSM. [2]
6 September 1941:
Requisitioned by the IJN.
20 September 1941:
Registered as an auxiliary netlayer attached to the Sasebo Naval District under internal order No. 1093.
15 October 1941:
Attached to the Mako, Pescadores, Formosa (now Magong, Penghu Islands, Taiwan) Guard District under instruction No. 1253. Tactically assigned to Vice Admiral Yamamoto Koki (36) Mako Guard District, Mako Naval Base, Mako Base Defense Unit.
17 October 1941:
Wakamatsu. Conversion for military duty is completed at Tochiki shipyard.
20 November 1941:
Tactically assigned to the Mako Guard District, Mako Base Defense Unit. Attached to Takao, Formosa (now Kaoshiung, Taiwan) Area Defense Force under secret Mako Guard District Order.
25 December 1941:
Assigned to anti-submarine sweeping in the second channel from 1000 until submarine depot ship CHOGEI has passed through.
December 1941: January 1942:
At Mako.
13 January:
Scheduled to carry out an anti-submarine sweep in the first channel on 14 Jan ‘42 from 0800 until fleet departure.
15 January 1942:
Attached to Takao Area Defense Force under secret Mako Guard District Order No. 7.
Receives secret Mako Guard District Order No 8:
Secret Mako Base Defense Unit Order No. 7 attachment 1 shows Mako Guard District Military Force Department table with auxiliaries to be transferred to Takao and Kirun (now Keelung) Area Defense Units. Ships to be transferred on 28 Jan ‘42 from Mako are auxiliary gunboat SENYO MARU, auxiliary subchasers AKITSU and ENSUI MARUs and auxiliary netlayer SEIKO MARU.
28 January 1942:
Departs Mako for Takao.
E 1 ~ 13 February 1942:
Departs Takao to her patrol area.
14 February 1942:
Arrives at Takao.
15 February 1942:
Departs Takao to patrol area.
18 February 1942:
Adrift off Haikow (Haikou), Hainan Island, China because of a main engine failure.
Receives Mako Guard District Order No. 11:
Commander of Mako Base Defense Unit sends one of her attached vessels in Mako port to Haikow’s coast as soon as ready and takes auxiliary netlayer SEIKO MARU which has a main engine failure to Haikow port. Thereafter she should be towed to Takao.
10 April 1942:
Attached to Mako Base Defense Unit under internal Order No. 658.
17 April 1942:
Be vigilant from 22 ~ 23 April of Prince Takamatsu’s aircraft in Takao under Mako Police Department Secret Message No. 486. Depart as soon as preparations are completed on rescue mission of a mud barge towed by auxiliary gunboat SENYO MARU.
20 April 1942:
At 0730, starts towing mud barge.
23 April 1942:
At 0650, hands over current towing to auxiliary gunboat SENYO MARU. Then, heads towards Takao where she arrives later this day.
14 July 1942:
Attached to Takao Base Defense Unit under secret Mako Guard District Order No. 43.
14 ~ 31 July 1942:
At Takao.
7 August 1942:
Receives secret Guard District Order No. 74: Commander of Takao Base Defense Unit sends auxiliary netlayer SEIKO MARU as soon as possible to a 100-tons vessel built by Tainan Suda Tetsu Kosho. It should be towed from Anping, Formosa (now Taiwan) to key location F and handed over to Mako director of naval design. director of the Mako naval engineering and director of Mako naval architecture will cooperate.
E 8 August ~ 12 August 1942:
Departs Anping district towing a mud barge.
13 August 1942:
Arrives at key location F.
25 August 1942:
At 1405, auxiliary gunboat SENYO MARU sinks at 22-23N, 120-10E about 16 nautical miles WSW Takao harbor after being torpedoed by Lt.Cdr. (Cdr/MOH, posthumously) Howard W. Gilmore's (USNA'26) USS GROWLER (SS-215). One crewman is KIA. Conducts rescue mission for torpedoed auxiliary gunboat SENYO MARU. Drops six depth charges.
26 August 1942:
Drops six depth charges.
31 August 1942:
Rated as Sea Defense Force Unit under Secret Mako Guard District Order No. 51.
7 ~ 9 September 1942:
Undergoes First combined training exercise.
28 September ~ 1 October 1942:
Undergoes Second combined training exercise.
21 October 1942:
At around 0120, at 24-26N, 120-26E IJA transport AFRICA MARU carrying 7,568-ton of corn and general cargo, sinks after being torpedoed by LtCdr Jesse L. Hull’s (USNA ’26) USS FINBACK (SS-230) on the previous day. Three crewmen are KIA.
Receives telegram No. 74 from Mako Guard District (amended partly by Mako Secret Guard Office Message No. 211620): 1 – Army transport AFRICA MARU has been torpedoed and sank at around 0120, on the 21st at 24-26N, 120-26E. 2 – Commander of Base Defense Unit should use all his ships to search and destroy enemy and rescue as much as possible survivors.
Departs Mako on anti-submarine sweep later that day.
23 October 1942:
Receives Mako Guard District Telegram No. 76: 1 - From 0800 onwards, sweeping under telegram No. 72 and No. 74 ends. 2 - Base Defense Unit ships should return to Mako while continuing with their anti-submarine sweep.
28 ~ 30 October 1942:
Undergoes Fourth combined training exercise.
December 1942:
In drydock.
28 December 1942:
LtCdr (later Vice Admiral) Vernon L. Lowrance's (USNA '30) USS KINGFISH (SS-234) torpedoes and sinks civilian merchant ship CHOYO MARU (5,388 GRT) off Formosa NW coast. One crewman is KIA.
29 December 1942:
Receives Mako Guard District Telegram No. 68: 1 - Kirun Defense Base Unit ships are rescuing civilian merchant ship CHOYO MARU (5,388 GRT) which was hit by a torpedo at 298° and 5 nautical miles of Baishajia Lighthouse, Formosa (now Taiwan).
2 - SEIKO MARU, minelayer ENJIMA and Port Affairs Department No. 6 and No. 5 tugboats will leave port as soon as they are ready and rescue team commander will be designated as the SEIKO MARU CO.
Receives Mako Guard District Telegram No. 93:
1 - Telegram No. 92: civilian merchant ship CHOYO MARU (5,388 GRT) is torpedoed by an enemy submarine and sank. 2 - Minelayers SOKUTEN and ENTO and auxiliary netlayer SEIKO MARU attack the enemy submarine. 4 - Rescue mission cancelled under Headquarters Order No. 68.
Receives Mako Guard District Telegram No. 94:
1 - From 29th afternoon classified anti-submarine sweep patrol will be carried out under Mako Guard District Order No. 57. 2 – Anti-submarine sweep continues under telegram No. 93.
29 ~ 31 December 1942:
Carries out assigned anti-submarine sweep.
31 December 1942:
Patrols as well as anti-submarine sweeps carried out under telegrams No. 93 and No. 94 are cancelled under Mako Guard District Telegram No. 96.
11 ~ 13 January 1943:
Undergoes third combined training exercise.
25 ~ 28 January 1943:
Undergoes fourth combined training exercise.
4 ~ 6 February 1943:
Undergoes fifth combined training exercise.
24 ~ 26 February 1943:
Undergoes sixth combined training exercise.
11 March 1943:
Receives Mako Guard District Telegram No. 16: 1 - On 11 Mar ‘43 at 0735, an enemy submarine is detected at a convex angle of 155° and approximately 15 feet away.
2 - Commander of the Base Defense Unit should attack with all his might.
15 March 1943:
Anti-submarine sweep carried out under Mako Guard District Telegram No. 16 ends under Mako Guard District Telegram No. 17.
17 March 1943:
Lt.Cdr. (later Vice Admiral) Vernon L. Lowrance's (USNA '30) USS KINGFISH (SS-234) torpedoes and damages IJN general requisitioned transport TENRYUGAWA MARU in the Formosa Strait.
18 March 1943:
Receives Mako Guard District Telegram No. 19: 1 – On 17 Mar ’43, at 2335, IJN general requisitioned transport TENRYUGAWA MARU was torpedoed by an enemy submarine at 24-30N, 120-09E.
2 – Commanders of Sea Defense Bases Units should entrust them with mop up attacks using ships.
19 March 1943:
Rescue work and anti-submarine sweeping carried out under Mako Guard District Telegram No. 19 is cancelled under Guard District Telegram No. 23.
1 April 1943:
Attached to the Mako Guard District, Mako Naval Base Force under internal order No. 588.Tactically assigned to Takao Base Defense Unit, Mako Guard District Special Base Unit. Attached to Mako Guard District, Defense Unit under secret Takao Base Defense Unit Order No. 6.
12 ~ 15 April 1943:
Undergoes ninth combined training exercise.
26 ~ 30 April 1943:
Undergoes tenth combined training exercise.
20 ~ 22 May 1943:
Undergoes twelfth combined training exercise.
1 June 1943:
Attached to Kirun Base Defense Unit, to be implemented on 8 Jun ‘43 under secret Takao Base Defense Unit Order No. 15.
3 ~5 June 1943:
Undergoes thirteenth combined training exercise.
8 June 1943:
Attachment to Kirun Base Defense Unit under secret Takao Base Defense Unit Order No. 15 is implemented.
8 ~ 10 July 1943:
Undergoes fifteenth combined training exercise.
28 ~ 31 July 1943:
Undergoes sixteenth combined training exercise.
9 ~ 11 August 1943:
Undergoes seventeenth combined training exercise.
13 August 1943:
Departs Kirun escorting tug KIRUN MARU (1901).
14 August 1943:
Arrives at Takao.
25 ~ 28 August 1943:
Undergoes eighteenth combined training exercise.
6 ~ 11 September 1943:
Undergoes nineteenth combined training exercise.
15 ~ 18 September 1943: On an aircraft rescue mission.
22 September 194:
Attached to Kirun Base Defense Unit, to be implemented on 1 Oct ‘43 under secret Takao Base Defense Unit Order No. 21.
27 ~ 29 September 1943:
Undergoes twentieth combined training exercise.
1 October 1943:
Attachment to Kirun Base Defense Unit under secret Base Defense Unit Order No. 21 is implemented.
2 October 1943:
Assigned to carry out an anti-submarine sweep at 25-15N, 121-46E under Takao Base Defense Unit Telegram No. 312.
5 October 1943:
current anti-submarine sweep will be cancelled if enemy is not destroyed by 1600 under Takao Base Defense Unit Telegram No. 317.
7 ~ 10 October 1943:
Undergoes twenty-first combined training exercise.
10 October 1943:
Assigned to carry out an anti-submarine sweep under Base Defense Unit Telegram No. 336.
12 October 1943:
Current anti-submarine sweep will be cancelled if enemy is not destroyed by 1600 under Takao Base Defense Unit Telegram No. 340.
13 ~ 14 October 1943:
Escorts a convoy.
15 October 1943:
Assigned to carry out an anti-submarine sweep at 24-30N, 120-30E under Takao Base Defense Unit Telegram No. 344.
16 October 1943:
Assigned to carry out an anti-submarine sweep at 25-13N, 121-57E under Takao Base Defense Unit Telegram No. 352.
19 October 1943:
Current anti-submarine sweep will be cancelled if enemy is not destroyed by 1200 under Takao Base Defense Unit Telegram No. 362.
26 ~ 28 October 1943:
Undergoes twenty-second combined training exercise.
10 November 1943:
Attached to Vice Admiral Mikawa Gunichi’s (38) Second Southern Expeditionary Fleet under internal order No. 2381. Tactically assigned to Vice Admiral (later Admiral) Takasu Shiro’s (35), Southwest Area Fleet, in Vice Admiral Mikawa Gunichi’s (38) Second Southern Expeditionary Fleet.
15 November 1943:
Detached from Kirun Base Defense Unit under secret Takao Base Defense Order No. 27.
November 1943 ~ December 1943:
Undergoes ship hold modification for transportation mission.
24 January 1944:
At 0700, arrives Waingapu with auxiliary transport CHOI MARU.
13 February 1944:
Departs Kendari, Celebes, Netherland East Indies (now Sulawesi, Indonesia) with auxiliary transport CHOI MARU escorted by auxiliary subchaser SHONAN MARU No. 17.
15 February 1944:
At 1600, arrives at Ambon, Moluccas, Netherlands East Indies (now Indonesia) with auxiliary transport CHOI MARU escorted by auxiliary subchaser SHONAN MARU No. 17.
19 February 1944:
At 0300, departs Ambon escorted by auxiliary subchaser SHONAN MARU No. 17.
20 February 1944:
At 1400, arrives at Tua (Tual or Toeal), Kai (Kei) Islands, Netherlands East Indies (now Indonesia) escorted by auxiliary subchaser SHONAN MARU No. 17.
25 May 1944:
Attached to Vice Admiral Yamagata Seigo’s (39) Fourth Southern Expeditionary Fleet under internal order No. 708. Tactically assigned to Admiral Takasu Shiro’s (35), Southwest Area Fleet, in Vice Admiral Yamagata Seigo’s (39) Fourth Southern Expeditionary Fleet.
5 June 1944:
Departs Kau, Halmahera, Moluccas, Netherlands East Indies (now Indonesia) and arrives at Wasile, Halmahera later this day.
6 June 1944:
At 0500, departs Wasile escorted by destroyer HOKAZE.
10 June 1944:
At 1400 arrives at Ambon. Rated as attached under secret Fourth Southern Expeditionary Fleet order No. 20. Rated as northern attached unit under secret Combined Fleet Order No. 8 .
17 June 1944:
At 0300, departs Ambon escorted by auxiliary subchaser TAKUNAN MARU No. 5.
19 June 1944:
At 0750, arrives at Boeroe (Boela or Buru), Moluccas, Netherlands East Indies (now Indonesia) escorted by auxiliary subchaser TAKUNAN MARU No. 5.
21 June 1944:
At 0500, departs Boeroe escorted by auxiliary subchaser TAKUNAN MARU No. 5.
23 June 1944:
At 1800, arrives at Ambon escorted by auxiliary subchaser TAKUNAN MARU No. 5.
July 1944:
Navy Lt. Oguri Saburo is appointed CO.
1 July 1944:
Rated as attached under secret Fourth Southern Expeditionary Fleet Order No. 22.
7 July 1944:
At 0500, departs Ambon escorted by subchaser CH-53.
9 July 1944:
Temporarily anchors at Woka anchorage (between W side of peninsula Woka and Woka Island, Obi Island, Moluccas (now Indonesia) because of mechanical problems.
11 July 1944:
Departs Payahi (now Payahe), Halmahera and calls at Ternate, Moluccas, Netherlands East Indies (now Indonesia). Departs there escorted by auxiliary subchaser NITTO MARU No. 18 and arrives at Loloda Bay, Halmahera later this day.
13 July 1944:
At 1200, arrives at Kau escorted by auxiliary subchaser NITTO MARU No. 18.
21 July 1944:
Departs Kau.
23 July 1944:
Arrives at Ternate.
25 July 1944:
Rated as attached northern unit under secret Combined Fleet Order No. 14 .
26 July 1944:
Departs Tawa (Tawang) Island, Moluccas, Netherlands East Indies (now Indonesia).
27 July 1944:
At 1630, arrives at Ambon.
1 August 1944:
Lt Norman L. Paxtons’ USN PBY-5 (Black Cat) of VP-34 attacks a Japanese transport (auxiliary ammunition ship SEIA MARU) and two escorts (minesweeper W-12 and subchaser CH-53). He sinks auxiliary ammunition ship SEIA MARU 20km E of N entrance of Chapalulu (Tjapaloeloe) Strait, Sula (Soela) Islands, Netherlands Indies (now Indonesia). 41 passengers and 22 crewmen are KIA.
Assigned to rescue auxiliary ammunition ship SEIA MARU as soon as ready under secret Combined Fleet Order No. 169 .
Departs Ambon with auxiliary subchaser CHa-116 (ex-Netherlands minesweeper C) on auxiliary ammunition ship SEIA MARU rescue mission.
3 August 1944:
At 01-47S, 126-15E auxiliary subchaser CHa-116 ends escort. At 0225, outside Tobabi Port, Tobabi Island, N coast of Mangole Island, Sula Islands LtCdr James A. Adkins’ (USNA ‘26) USS COD (SS-24) at 01-46S, 126-15E, fires 4 torpedoes of which three hit SEIKO MARU. She sinks within half an hour. Auxiliary subchaser CHa-116 drops 4 depth charges and then leaves sinking area. At 0304, USS COD surfaces and circles through oil slick. A lot of debris, a lifeboat and many survivors in the water are seen. Around 0400, USS COD departs. 56 passengers and two crewmen are KIA.
10 March 1945:
Removed from the Navy’s list under internal instruction No. 232.

Authors' Notes:
[1] Not to be confused with civilian cargo ship (6,890 GRT, ’45) and general requisitioned (B-APK) passenger/cargo ship (5,385 GRT, ’40).
[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.
Thanks go to Gengoro S. Toda of Japan.

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

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