Osaka Iron Works K.K. for Dairen Kisen K.K. as a 5,461-tons cargo vessel. Launched on February 12, 1939 as Sanko Maru. Completed on May 8, 1939 and registered at Dairen (Dalian).
On December 3, 1940 requisitioned by the Imperial Japanese Navy (IJN) instruction No. 980 for use as a auxiliary collier/oiler attached to the Kure Naval District based at Kure.
On February 5, 1944 arrives at Palau and the next day HA-52 Type B midget submarine was transfered from Kizugawa Maru to Sanko Maru.
On February 12, 1944 departs Palau towing HA-52 Type B midget submarine as part of "Convoy SO-903" with Tatsukiku Maru, Shinto Maru No. 1 escorted by subchasers CH-22, CH-39 and CHA-16 bound for Rabaul. Off Mussau Island, Sanko Maru towing HA-52 escorted by subchaser CH-39 detach for Kavieng.
On February 16, 1944 off Three Island Harbor on the northeast side of New
Hanover, Sanko Maru towing HA-52 escorted by CH-39 were spotted and attacked by B-25 Mitchells from the 345th Bombardment Group, 500th Bombardment Squadron that strafe and sink Sanko Maru, HA-52 and CH-39.
Later that afternoon, the same B-25 return and again strafe CH-39 exploding it and further strafe HA-52 claiming it as sunk.
This vessel is lying on its starboard side on a sandy bottom covered with sea fans and soft corals at a depth of 22m. During 1987, HA-52 Type B midget submarine was discovered 50m off the main mast.
Some sources incorrectly identify this vessel as "Taisyo Maru" incorrectly.
Combined Fleet - IJN SANKO MARU: Tabular Record of Movement
Combined Fleet - Midget Submarines in the Bismarcks 1943-1944
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August 18, 2018