 Following the sinking of sister gunboat off Nanking by Japanese planes 12 December 1937, "Oahu" picked up the survivors and carried them to Shanghai, returning to the scene of the incident to conduct salvage operations.As the Japanese campaign in China grew, the gunboat operated only on the lower river as far as Wuhu and Hankow, in addition serving as station ship and radio relay vessel for American officials at the temporary U.S. embassy at Nanking.Whenever the warship attempted to cruise the river on regular patrol, she was convoyed by Japanese minesweepers that kept watch on her movements while protecting her from attacks by their planes.