She was laid down on 12 July 1941, at the Hong Kong shipyard of Taikoo Dockyard and Engineering Company as HMS Portland.[3][2][4] In September 1941, while still under construction, she was renamed HMS Taitam.[3] On 26 December 1941, still unfinished, she was seized by the Japanese after the Fall of Hong Kong.[3] The Japanese continued construction and she was launched on 20 February 1943 and renamed W-101.[3] On 10 April 1944, she was completed, commissioned, and attached to the Yokosuka Naval District under Lieutenant Commandeer Ginji Yamashita.[3][5]
On 17 November 1944, in the Yellow Sea off Cheju Island, MI-27 was spotted by US submarines Sunfish and Peto which were operating in a wolfpack with Spadefish.[3]Sunfish torpedoed and damaged both Edogawa Maru and Seisho Maru while Peto torpedoed and sank Osakasan Maru (killing 142).[3] Nearby, Spadefish spotted Shin'yō of HI-81 and fired six torpedoes four of which hit causing the carrier to burst into flames and sink (killing 1,130).[7]W-101 and CD-61 were disattached from MI-27 to pick up survivors.[7] On 18 November 1944, Sunfish torpedoed and sank the damaged Seisho Maru (killing 448) and the damaged Edogawa Maru (killing 2,083); while Peto torpedoed and sank Chinkai Maru (killing 39).[3] After losing four of the eight ships being escorted, the remainder of convoy MI-27 arrived at Sijiao Island on 19 November 1944.[3]
Convoy Tama-33
On 30 November 1944, W-101 departed Takao for Manila escorting landing craft depot ships Shinshū Maru and Kibitsu Maru along with escorts Tsushima, the Ukuru-class escort shipDaito, and four Type D escort ships (CD-14, CD-16, CD-46, and CD-134). The convoy diverted and disembarked its troops at San Fernando, Luzon due to enemy air attacks at Manila.[3]
Convoy HI-85
On 29 December 1944, she joined convoy HI-85 in the South China Sea consisting of the light cruiser Kashii, two Ukuru-class escort ships (Ukuru and Daito), and three Type C escort ships (CD-23, CD-27, CD-51) in escorting nine tankers (Enkei Maru, Yamazawa Maru, Engen Maru, Encho Maru, Daigyo Maru, Otususan Maru, Fuei Maru, Oei Maru, Seria Maru) and one cargo ship (Shinyu Maru).[3] After several unsuccessful attacks by B-24 Liberator bombers, the convoy arrived at Cap Saint-Jacques on 4 January 1945.[3]