Built by Fujimagata Dockyard, Osaka and launched in 1921 as Shin-ai Maru.[1] She was renamed Sin-ai Maru in 1938.
She left Rabaul, New Britain on 1 March 1943, as part of Operation 81, carrying a cargo of troops, equipment, fuel, landing craft and ammunition for Lae, New Guinea.[2] The convoy was attacked by aircraft of the United States Army Air Forces and Royal Australian Air Force from 2 March 1943, known as the Battle of the Bismarck Sea. Sin-ai Maru was bombed on 3 March and sank at 07°15'S., 148°30'E.
18 crew, 45 gunners and an unknown number of troops were KIA.[3]