"Robalo" departed Fremantle on 22 June 1944 on her third war patrol. She set a course for the South China Sea to conduct her patrol near the Natuna Islands. After leaving Makassar Strait and Balabac Strait (which was known to be mined), she was meant to arrive about 6 July and remain there until dark on 2 August 1944. On 2 July, a contact report stated "Robalo" had sighted a "Fusō"-class battleship, with air cover and two destroyers for escort, just east of Borneo. No other messages were ever received from the submarine and when she did not return from patrol, she was presumed lost.