On October 19, 1944, Toun Maru departed Shanghai en route to Takao. She temporarily anchored Pinghai Wan, and at 1650 on October 22, 1944, weighed anchor. On October 23, 1944, at 0337 in position 24.49N 120.26E, about 100km ESE of Nanri Dao, the ship was torpedoed and set on fire. The ship did not sink and drifted till the vessel arrived at Mako. At the time of attack the ship was carrying 297 landing troops of whom 131 were killed, along with 5 passengers, 12 ship’s gunners and 16 crew.

The wreck was not able to be repaired and was discarded. The submarine was USS Tang. It is probable there were 229 troops and the rest were passengers. The wreck was scrapped on December 13, 1944, after first being towed to Mako and then to Takao.