Taisei Maru was owned by Osaka Shoen K. K. with the number "4" painted on the smoke stack. Prewar, used as a cargo vessel. During the Pacific War, this vessel was chartered by the Imperial Japanese Navy (IJN) as cargo vessel.
On April 6, 1943 at 1630, convoy "Hansa No. 28" departs Palau bound for Hansa Bay. The convoy includes subchaers CH-26 and CH-34 destroyers Tanikaze and Amatsukaze plus transports Teiryu Maru, India Maru, Toho Maru, Sydney Maru, Taisei Maru and Taiyu Maru.
On April 12, 1943 the convoy arrives at Hansa Bay and is attacked, and the Sydney Maru is sunk. The next day at 9:00am the convoy departs Hansa Bay and splits up with Teiryu Maru, Toho Maru and Amatsukaze and CH-34 proceeding to Palau and arriving on April 18, 1943. The other ships CH-26, Tanikaze, Taisei Maru and Taiyu Maru proceeded to Wewak to unload their remaining supplies on April 14, 1943. The next day while underway to Palau, the India Maru is sunk. The remainder of the convoy reaches Palau on April 20, 1943.
On September 19, 1943 "Wewak No. 9" convoy departs Palau consisting of Taisei Maru, Aden Maru and Yasukuni Maru escorted by subchaser CH-26 and CH-32. On September 23, 1943 the convoy arrives at Wewak and begin unloading cargo. The subchaser escorts depart on the 24th for Palau.
On September 27, 1943 B-25 Mitchells from the 3rd Bombardment Group, attacked the Taisei Maru at low level, sinking it into Victoria Bay west of Kairuru Island. During the attack, twenty-three soldiers and two crewmen are killed.
This shipwreck is upright on a sandy bottom. Reported as 90m long, on a 37m bottom, with the deck at 25m. The superstructure shows bomb damage, and a lot of fish and coral life. The bow section with an anchor still attached, hanging down to the sand.
It is possible this wreck was salvaged in the 1950s by Japanese for scrap metal and removing the masts.
David Morgan adds:
"The Taisei Maru and the name was visible on the stern at the time of my dive."
Ken Howard dove in 2004:
"I can't compare this Maru to other PNG wrecks, but it was certainly one of the highlights of our 12 days of diving from Madang to Wewak, and ranks up there (photographically). The viz wasn't all that great (maybe 50 feet)--despite this wreck's size, you had to start down the line attached to the marker buoy because you couldn't spot the wreck from the surface. I was first in the water on both dives, and as I mentioned didn't venture inside the wreck. The second (bow) dive had noticeably worse viz, after the other eleven divers had been in the water. Water conditions were calm, however."
Justin Taylan dove in 2006:
"Locals refer to this wreck as Musao Maru, and charge 5 Kina per diver. It appears the wreck was salvaged post war. The propeller is missing, and appears that it might have had salvage done on it. The remains of the kingpost is present, but collapsed into the wreck."
Other sources state this ship was sunk off the Schouten Islands incorrectly
Combined Fleet IJA MAYA MARU Tabular Record of Movement
Combined Fleet ADEN MARU Tabular Record of Movement
X Marks The Spot research by David Pennefather
Thanks to David Pennefather, David Morgan, Ken Howard and Justin Taylan for additional information
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August 4, 2020