The submarine's sixth war patrol, 23 September to 8 December, took her to the familiar waters of the South China Sea. On 6 October and 7 October, she twice torpedoed a tanker, inflicting undetermined damage. Five days later, she destroyed the cargo ship "Toko Maru" with two direct hits and escaped a subsequent depth charge attack. On 14 October, while making a crash dive to escape a Japanese patrol plane, "Ray"'s conning tower was flooded by an improperly secured hatch, but she was brought under control before reaching . However, the damage forced the submarine to put into Mios Woendi for repairs during the last week of October.