For her second patrol, "Robalo" went to the South China Sea, with the job of stopping Japanese oil tankers sailing from French Indochina to the fleet anchorage at Tawi Tawi. On 24 April 1944 off Indochina she was bombed by a Japanese antisubmarine aircraft. The "Robalo" had been seen by Japanese aircraft carrier Kaiyō which was escorting convoy Hi-58. In trying to escape the submarine dived quickly down to 350 feet (110 m), but the main entry hatch was not closed properly. The periscopes were damaged and flooded, her radar stopped working. A similar failure to close the main hatch had caused the submarine "Squalus" to sink with the loss of 26 sailors in 1939. 