On 6 July, "Ōi" departed Surabaya for Manila. On 19 July, she was sighted in the South China Sea, south of Hong Kong by the United States Navy submarine . When the cruiser was astern, "Flasher" fired her four stern tubes, hitting "Ōi" with two torpedoes portside aft. One was a dud, but the other torpedo exploded and flooded "Ōi"s aft engine room. "Flasher" then fired four bow torpedoes from , but all missed. At 17:25, "Ōi" sank by the stern at . The destroyer "Shikinami," which had attempted to tow the stricken cruiser to safety before she broke in two and sank, rescued Captain Shiba and 368 crewmen, but another 153 crewmen went down with the ship.