On 27 October 1943, "Ro-105" began her third war patrol, departing Rabaul bound for a patrol area off Mono Island in the Treasury Islands. On 1 November 1943, the Bougainville campaign began with U.S. landings at Cape Torokina on Bougainville, and a Japanese attempt to bring reinforcements to Bougainville resulted in the Battle of Empress Augusta Bay on 2 November 1943. "Ro-105"′s lookouts observed star shells and gun flashes from the battle in the distance early in the morning of 2 November. The Japanese light cruiser and destroyer were sunk during the battle, and later on 2 November 1943 "Ro-105" received orders to search for their survivors. She found bodies in the water but no living Japanese, although she did rescue two downed Japanese naval aviators from a life raft southeast of New Britain on 6 November 1943. She arrived at Rabaul on 9 November 1943.