Completing shakedown training at New London, Connecticut, "Sea Devil" departed that port on 11 July 1944 and arrived at her home port, Pearl Harbor, on 9 August to join Submarine Division (SubDiv) 281 and prepare for her first war patrol. On 3 September, she sailed west. By 15 September, she was off Honshū, and, during the early morning darkness, made contact with her first enemy ships — two sampan-type patrol vessels. Rough seas, however, precluded an attack, and she continued on to patrol in the shipping lanes to Japan's major ports: Yokohama, Kobe, and Osaka.