Stories and Battle Histories of the IJN's Converted Small Minelayers

3 September 2019

By Berend van der Wal, Gilbert Casse and Peter Cundall

with Bob Hackett

Discussion & Questions

(KATSURA MARU under air attack 31 January 1944)

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 some became Tokusetsu Fusetsutei, (Converted Small Minelayers). The main task of a minelayer is to lay mines. During the war these ships were also used for minesweeping, patrol, escort, anti submarine and transport tasks. Between 1937 and 1945 eight merchant ships were used as Tokusetsu Fusetsutei by the IJN.

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 UnŽeikai (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.

Tabular Records of Movement (TROMs):
IJN Converted Fusetsutei :

(Classes link to specifications summaries)


Kinjo Maru
(posted 1 March 2018)

Choan Maru
(posted 1 August 2018)


Kosei Maru
(posted 2 May 2019)


Minsei Maru
(posted 6 June 2019)


Urara Maru
(posted 6 June 2019)


Takachiho Maru
(posted 3 September 2019)

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 and convoys. He resides in Australia and works in the maritime industry.

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