The troopship was part of convoy HI-72 and transporting 1,317 Australian and British prisoners of war (POWs) from Singapore to Formosa (Taiwan).Another ship in the convoy was SS Kachidoki Maru with another 950 Allied POWs and 1,095 Japanese on board.[1]
On the morning of 12 September 1944, the convoy was attacked in the Luzon Strait by a wolfpack consisting of three US submarines:, and . Rakuyō Maru was torpedoed by Sealion and sunk towards the evening. The Kachidoki Maru was also sunk with 488 people killed, mostly POWs. The Japanese survivors of the Rakuyō Maru were rescued by an escort vessel, leaving POWs in the water with rafts and some abandoned boats. A total of 1,159 POWs died, including sportsman Winston Ide and Brigadier Arthur Varley. 350 of the dead were bombarded in lifeboats and killed by a Japanese navy vessel the next day when they were rowing towards land.[2] On 15 September, the three submarines returned to the area and rescued 149 surviving POWs who were on rafts.[3] Four others died before they could be landed at Tanapag Harbor, Saipan, in the Mariana Islands.[2] [4]