She was launched on 27 October , sponsored by Mrs. After a six-week training period in New London, Conn. At the end of a brief refit alongside submarine tender Fulton , Balao got underway on 25 July to begin her first war patrol. She topped off her fuel tanks from submarine rescue vessel Coucal on 29 July, and on 7 August took station in the scouting line in the sealanes between Truk and the Bismarck Archipelago. However, she made only five enemy contacts and was unable to launch a single attack.
The scouting line was discontinued on 26 August, and Balao shifted to patrol the Palau β Rabaul shipping route where she fared no better. The submarine trained in emergency dives, and her crew frequently went to battle stations upon the sighting of enemy aircraft; but the patrol was not enlivened by action with surface ships before the boat moored alongside Fulton in Brisbane on 13 September for refit.
Her second war patrol began on 4 October when Balao sailed in company with Silversides for Tulagi. After refueling there on 11 October, the submarine got underway for her assigned area north of the Bismarck Archipelago and again covered the Palau-Rabaul routes. Balao sighted a convoy on 17 October, but it escaped her salvo of six torpedoes by making a radical zig-zag maneuver and increasing speed to open the range. The convoy's escorts counterattacked with depth charges , but Balao came away unscathed.
Her targets moved out of range at high speed, preventing her from regaining contact. Balao joined Silversides in a coordinated attack on a seven-ship convoy on 23 October, firing 10 torpedoes at three ships that presented an overlapping target. She scored six hits. One ship was seen down by the bow, with her stern in the air; another listed heavily; and a third was riding low in the water. While Balao was maneuvering into position for a second attack, the convoy's escorts fired on her, forcing the submarine to dive.
Balao lost contact with the convoy and failed in her attempts to reach Silversides to exchange information. She later learned, however, that her consort sank three of the seven ships.
