TOKUSETSU KOKAI HOKAN!

Stories and Battle Histories of the IJN's Converted High Seas Auxiliary Gunboats

1 April 2024

By Berend Van der Wal, Gilbert Casse and Peter Cundall

with Bob Hackett

Discussion & Questions

(Auxiliary gunboat CHOSA MARU in wartime from Berend van der Wal collection)

Prior to and during the Pacific War, the Imperial Japanese Navy enlisted some of Japan's merchant fleet's cargo, passenger-cargo ships and liners. They were converted to military use and became Tokusetsu Kokai Hokan, (Converted High Seas Gunboats). They were used to escort ships, to patrol, to lay mines, to guard, to pilot ships, to transport people and goods to other ships and bases and to execute anti-submarine warfare. Between 1937 and 1945 eighty five merchant ships were used as Tokusetsu Kokai Hokan by the IJN. Some were later released to their owners or reconverted to perform other military tasks.

Other ships were also requisitioned by the IJN but not enlisted. They were called Ippan Choyosen (General Requisitioned Ships) and manned by civilian crews. IJA and the civilian shipping administration requisitioned many other ships.

To summarize, during the war employment of ex-merchant ships was divided into three main administrative categories:
A = requisitioned and operated by the Japanese Army and named Rikugun Yusosen (IJA Transports). They include Cargos, Passenger-Cargos, Liners and Tankers.

B = requisitioned and operated by the Japanese Navy with civilian crew (captain often being Navy Reserve). These are named Ippan Choyosen.

C = controlled and operated by the Senpaku Un´eikai (Civilian Shipping Administration).

X = requisitioned by the IJN and converted into armed Naval Auxiliaries with IJN crews (gunboats, minesweepers, etc.) and named Tokusetsu Kansen followed by another suffix for the ship’s use.

Beside the above categories, there were many shared employments Army/Civilian (A/C) and Navy/Civilian (B/C). These ships were respectively called Rikugun Haitosen and Kaigun Haitosen. Normally, this meant that the vessel on its outbound journey was under Army or Navy control carrying troops, military supplies, etc. and on its return voyage was carrying cargo for the benefit of the civilian owner of ship. While used by the Army, the Haitosen also received Army transport numbers like Army requisitioned vessels (A). Employments by Army or Navy could also be expanded, meaning that the ship was used by Army/Navy for one full turn (outward and homeward voyage) or even a series of voyages.

This page will cover the activities of the eighty five IJN Converted Auxiliary High Seas Gunboats.



Tabular Records of Movement (TROMs):
IJN High Seas Auxiliary Gunboats (Kokai Hokan)
(Classes link to specifications summaries)

SHINKYO MARU Class

Shinkyo Maru (revised 24 September 2020)
Anshu Maru (revised 24 September 2020)
Seikyo Maru (revised 5 October 2020)
Nikkai Maru (revised 5 October 2020)
Daido Maru (posted 3 February 2021)
Kanko Maru (posted 2 October 2022)
Keiko Maru (posted 6 April 2023)

PEACETIME STANDARD TYPE (D) Class

Hirotama Maru (revised 19 March 2023)
Shoko Maru (revised 24 January 2017)
Katori Maru (posted 6 October 2012)
Shoei Maru No. 2 Go(posted 27 December 2017)

Meiji Maru No. 1 Go(posted 2 June 2018)

Choun Maru (posted 2 June 2018)
NACHI MARU Class

Nachi Maru (revised 20 August 2020)

RYOTOKU MARU Class

Ryotoku Maru
(posted 1 June 2014)

IKUTA MARU Class

Nagata Maru (revised 19 March 2023)

Ikuta Maru (posted 2 April 2022)

Manyo Maru (posted 2 October 2023)

SANTO MARU Class

Santo Maru (revised 6 May 2018)

UKISHIMA MARU Class

Ukishima Maru (revised 25 November 2017)



SHOEI MARU Class

Fukuyama Maru
(revised 21 September 2014)

KAZAN MARU Class

Tozan Maru
(posted 1 June 2014)
Kazan Maru
(posted 1 February 2023)

SHOEI MARU Class

Shoei Maru (revised 6 May 2018)

Shoho Maru (posted 1 August 2014)
HYAKUFUKU MARU Class

Hyakufuku Maru
(revised 17 August 2018)
TOSHO MARU Class

Tosho Maru
(revised 23 September 2018)
Daigen Maru No. 7
(revised 17 August 2018)
UNKAI MARU No. 10 Class

Unkai Maru No. 10
(revised 23 September 2018)
FUKUEI MARU No. 10 Class

Fukuei Maru No. 10(revised 17 August 2018)
KOWA MARU Class

Kowa Maru (revised 7 May 2016)

CHOJO MARU Class

Choan Maru No. 2 Go (revised 17 September 2017)
Choko Maru No. 2 Go (posted 1 November 2014)
HIROTA MARU Class

Yoshida Maru (revised 14 May 2016)
HIYOSHI MARU No. 2 GO Class

Hiyoshi Maru No. 2 Go (posted 1 December 2014)

Hokoku Maru (posted 8 December 2021)
FUKKEN MARU Class

Busho Maru (posted 1 February 2015)

Chosa Maru (posted 7 December 2020)

NISSHO MARU No. 2 Class

Nissho Maru No. 2 (posted 1 February 2015)

NISSHO MARU No. 16 Class

Nissho Maru No. 16 (posted 1 February 2015)
JUZAN MARU Class

Juzan Maru (posted 1 March 2015)



KIRI MARU No. 8 Class

Shinko Maru No. 1 Go(revised 9 December 2017)



SHOSEI MARU Class

Shosei Maru (revised 23 September 2018)

KAIHO MARU Class

Kaiho Maru (posted 2 May 2018)

USSB 1023 type (Sub Boats - RAMON MARU) Class

Ramon Maru (posted 4 October 2019)

KEISHIN MARU Class

Keishin Maru (posted 5 January 2020)

Peacetime C (HEIJO MARU) Class

Heijo Maru (posted 3 February 2020)

Keijo Maru (posted 5 March 2020)
KATSURA MARU No. 2 GO Class

Katsura Maru No. 2 Go (posted 3 April 2020)

SHOWA MARU Class

Kosho Maru (posted 5 May 2020)

HINO MARU No. 2 Class

Hino Maru No. 2 (revised 30 April 2016)

FUJI MARU Class

Aso Maru (revised 2 June 2020)

Kiso Maru (posted 3 July 2020)
CHITOSE MARU Class

Chitose Maru (posted 4 August 2020)

KONGOSAN MARU Class

Kongosan Maru (posted 4 June 2023)

Chohakusan Maru (posted 2 September 2020)

Chojusan Maru (posted 3 November 2020)

DELHI MARU Class

Delhi Maru (posted 10 March 2021)

HAKUTETSU MARU No. 11 Class

Edo Maru (posted 6 April 2021)

KOTO MARU No. 2 GO Class

Eifuku Maru (posted 2 June 2021)

HAKKAI MARU Class

Hakkai Maru (posted 2 August 2021)

KINSEN MARU Class

Hakkaisan Maru (posted 1 October 2021)

HONG KONG MARU Class

Hong Kong Maru (posted 8 February 2022)

KANAN MARU Class

Kahoku Maru (posted 3 June 2022)

KAMITSU MARU Class

Kamitsu Maru (posted 3 August 2022)

MAYA MARU Class

Kasagi Maru (posted 5 December 2022)

KOGANE MARU Class

Magane Maru (posted 6 August 2023)

MYOKEN MARU Class

Myoken Maru (posted 2 December 2023)

NAMPO MARU Class

Nampo Maru (posted 1 February 2024)

NISSHO MARU No. 12 Class

Nissho Maru No. 12 (posted 1 April 2024)



Bibliography of Sources

About the Authors

Mr. Berend van der Wal got interested in the Japanese Navy through his hobby ship modelling. He researches the Japanese Navy since 1978. He is an IT support engineer and resides in the Netherlands.

Mr. Gilbert Casse is a maritime historian and researcher. Retired from the aerospace industry, and later from managing Le Mans racing cars and drivers, his advocation is ship modelling, maritime photos and paintings. He resides on the SW coast of France.

Mr. Peter Cundall is a maritime historian and researcher who specializes in merchant ships. He resides in Australia and works in the transport industry.

Mr. Robert Hackett is a military historian and researcher. Retired from the United States Air Force and later from the aerospace industry, he resides on the coast of Florida.

Questions to the authors concerning these TROMs should be posted on the Discussion and Questions board.