(UNYO MARU No. 2 prewar)
IJN UNYO MARU No. 2:
Tabular Record of Movement
© 2013 Gilbert Casse, Bob
Hackett and Peter Cundall
22 March 1937:
Tama. Laid down by Mitsui Bussan K.K. Zosensho shipyard for
Nakamura Kisen K.K. as a 2,827-ton cargo ship.
25 July 1937:
Launched and named UNYO MARU NO. 2.
6 August 1937:
Completed and registered in Kobe.
2 November 1941:
Requisitioned by the IJN.
4 November 1941:
Begins conversion to military duty at Yokosuka Naval
10 November 1941:
Registered in the IJN as an auxiliary transport,
(Otsu) category and attached to the Yokosuka Naval District with Yokosuka as
homeport under internal order No. 1391. 
26 November 1941:
Conversion is completed.
Arrives at Camranh Bay, Indochina (now Vietnam).
13 December 1941: Operation "B" - The Invasion of British Borneo
The occupation of British Borneo is a combined IJN/IJA operation
which involves Gen (later Field Marshal) Count Terauchi Hisachi’s command’s
Southern Expeditionary Army. The 25th Army, under LtGen Yamashita Tomoyuki
fields MajGen Kawaguchi Kiyotake’s “Detachment” of about 2,500 men consisting of
the 35th Infantry Brigade HQ, the 124th Infantry Regiment led by Col Oka
Akinosuke, 18th Signal Unit platoon, 18th Medical Unit and 18/4 Field Hospital
Medical Unit. In addition, five specialized and supply units are embarked on the
transports: 21st Field Ordnance Depot Company and 1st, 2nd, 3rd & 4th Field Well
drilling companies of about 120 men each (oil well repairs). Finally,
one AA and one Signal Regiment are stationed on IJA transports.
The invasion units are embarked on IJA transports KATORI, HIYOSHI, MYOHO,
KENKON and NICHIRAN MARUs.
The Navy force consists of Vice Admiral (later Admiral) Kondo Nobutake's
(35)(former CO of KONGO) Southern Force, Borneo Invasion Group that includes
Rear Admiral (later Vice Admiral) Kurita Takeo's (38), Support Unit. Rear
Admiral (later Vice Admiral) Hashimoto Shintaro's (41) Invasion Unit consists of
UNYO MARU No. 2 transporting equipment material and supplies, the 4th Naval
Construction Unit of about 260 men and materials aboard TONAN MARU No 3, the
No.2 Yokosuka Special Naval Force (SNLF) aboard HOKKAI MARU. Other transports
are KAMIKAWA and MITAKESAN MARUs transporting equipment, material and supplies.
The convoy’s close escort consists of minesweepers W-3 and W-6 and
subchaser CH-7. Other escorts include CruDiv 7’s KUMANO and SUZUYA, light
cruisers YURA and KINU, Desdiv 11’s FUBUKI, DesDiv 12’s MURAKUMO, SHINONOME,
SHIRAKUMO and USUGUMO and DesDiv 20’s SAGIRI. Seaplane tender KAMIKAWA MARU with
six Mitsubishi Type 0 F1M “Pete” (plus two in reserve) and four Aichi E13A1
“Jake” (plus one in reserve) provides air cover.
At 0730, the Invasion Convoy departs Camranh Bay.
14 December 1941:
The Invasion Convoy crosses the South China Sea
without being sighted. MITAKESAN MARU is detached to the Philippines.
15 December 1941:
At 2330, the main body of the convoy arrives at
Miri anchorage. At midnight, HIYOSHI MARU arrives at Seria anchorage. About the
same time, all IJN transports arrive at Lutong. Because of a rainstorm, three
Daihatsu barges capsize when lowered into the water. 19 IJA landing troops are
KIA and 15 are MIA.
16 December 1941:
At 0440, troops land at Miri, Seria and Lutong.
Despite worsening weather conditions, landings are made without opposition from
British defending units and Miri, Seria and Lutong oilfields as well as Miri
airfield are all secured in the morning.
17 December 1941:
N of Miri, near Seria. Destroyer SHINONOME is
attacked by Dutch Dornier Do-24 K-1 flying-boat X-32 of Aircraft Group GVT-7
based at Tarakan, E Borneo. Of five 200-kg bombs she drops, the X-32 scores two
direct hits and a near-miss. An explosion severs SHINONOME's stern and she sinks
quickly with all hands - the first FUBUKI-class destroyer sunk in WWII.
A Do-24 X-34 flying boat of GVT-7 attacks a vessel, but is intercepted by
a Type O Mitsubishi F1M2 ‘Pete’ floa fighters from KAMIKAWA MARU. The Dornier is forced to
make an emergency landing with two of its crew dead. Two hours later, in bad
weather conditions, six Dutch Glenn Martin bombers of 2-VIG-I also attack. A
Pete from KAMIKAWA MARU attacks the Dutch bomber formation, but they escape. 
19 December 1941:
Miri. In the morning, Martin B-10 medium bombers
from 1-VIG-I and 2-VIG-I based at Samarinda and Singkawang attack the invasion
shipping. Four KAMIKAWA MARU’s F1M2 “Pete” fighters intercept separate trios
of bombers that appear at 15-minute intervals. The Petes’ pilots claim downing
Martin M-571 of 2-VIG-I.
20 December 1941:
Miri. About midday, six Martins of 2-VIG-I escorted
by two obsolete Brewster “Buffalo” fighters attack Japanese shipping off Miri.
The bomber crews miss a cruiser. F1M2s from KAMIKAWA MARU intercept and claim
one bomber. The Buffaloes escape with heavy damage.
That same day, an E13A1 Jake from KAMIKAWA MARU fails to return from a
22 December 1941: Operation “Q” - The Invasion of Sarawak (British
The main body of the Japanese invasion force (two battalions)
re-embarks at Miri. The invasion convoy departs for Kuching, Sarawak. The
invasion convoy consisting of UNYO MARU No. 2, HOKKAI, KATORI, HIYOSHI, MYOHO,
KENKON and NICHIRAN MARUs, TONAN MARU No. 3 and KAMIKAWA MARUs escorted by light
cruiser YURA, DesDiv 12's SHIRAKUMO, MURAKUMO and USUGUMO and minesweepers W-3
The invasion convoy is transporting the Kawaguchi Detachment (minus one
battalion) and the Yokosuka No. 2 Special Naval Landing Force (SNLF) aboard
HOKKAI MARU. UNYO MARU No. 2 is carrying material, equipment and supplies, TONAN
MARU No. 3 is carrying the 21st Field Ordnance Depot, the 48th Anchorage HQ, the
4th Naval Construction Unit of about 260 men.
CruDiv 7/1's KUMANO and SUZUYA, light cruiser KINU and destroyers FUBUKI
and SAGIRI provide the covering force. West of the covering force is CruDiv
7/2's MIKUMA and MOGAMI with destroyer HATSUYUKI. Seaplane tender KAMIKAWA MARU
provides air cover.
23 December 1941:
Early morning, about 150 miles from Kuching, a
Dutch reconnaissance aircraft spots the Invasion Convoy.
At 1140 that morning twenty-four Japanese aircraft bomb Singkawang II
airfield, so damaging the runways that a Dutch striking force which had been
ordered to attack the convoy is unable to take off with a bomb load.
At 1800, the convoy approaches the mouth of the Santubong river.
Subsequent landings are made again with little opposition from British Forces
although four Daihatsu landing craft are sunk. Moreover, both convoy and escorts
do not escape unscathed.
Off Kuching. At 2040, Dutch Ltz I Carel A. J. van Well Groeneveld's
submarine K-XIV attacks the anchored transports. He torpedoes and sinks in
sequence IJA transport HIYOSHI MARU with five crewmen KIA, and IJN transport
KATORI MARU with the loss of 10 crewmen and many troops. IJN transports HOKKAI
MARU and TONAN MARU No. 3 are also damaged by K-XIV’s torpedoes. HOKKAI MARU is
heavily damaged and beached to prevent her sinking. 
23/24 December 1941:
Near Kuching. About midnight, LtCdr L. J.
Jarman's Dutch submarine K-XVI torpedoes destroyer SAGIRI. The destroyer's own
torpedoes catch on fire and SAGIRI blows up, killing 121 officers and men. W-3
and destroyer SHIRAKUMO rescue 120 survivors.
25 December 1941:
Off Kuching. At 2300, Dutch Ltz I Carel A. J. van
Well Groeneveld's submarine K-XIV torpedoes and damages IJA transport NICHIRAN
MARU. At about 1640, the Japanese troops completely secure Kuching airfield.
26 December 1941:
Off Kuching. Three Dutch Army Glenn Martin B-10
bombers from Samarinda, Borneo bomb, set on fire and sink UNYO MARU No. 2 with
the loss of eight of her crew, and minesweeper W-6 at 01-34N, 110-21E.
Minesweeper W-3 participates in the rescue of an unknown number of W-6’s
15 January 1942:
Removed from the Navy’s list under instruction No.
 There were two categories of Zatsuyosen. (Ko) category
with an IJN Captain as supervisor aboard and (Otsu) category without.  The
survivors float in their dinghy for three weeks, finally getting ashore 260
miles to the south, where they become POWs. In 1945, shortly before the Japanese
capitulation, the crew is executed.
 One source indicates that TONAN MARU No. 3 made Saigon a few days
later for temporary repairs.
Thanks go to Gengoro S. Toda of Japan, Erich Muelthaler of Germany and
Allan Alsleben of Oregon.
Gilbert Casse, Bob Hackett and Peter Cundall
IJN Transports Page