"Barbero" embarked on her first war patrol from Pearl Harbor on 9 August 1944. She reached her patrol area, located east of the central Philippines off San Bernardino Strait, on 24 August. Though she had been stationed there to report and to interdict any attempt by the Japanese to use the strait to contest the Allied invasion of the Palau Islands, they tried no such move. Moreover, during the 31 days that she spent in the area, she encountered no large target. The high point of the patrol came when "Barbero" lobbed 25 rounds at a radar station on Batag Island with her 5"/25 caliber gun deck gun. Though she obtained no definite results, her failure to detect radar activity the following night prompted her claim to have neutralized the station. The submarine cleared the area on 24 September 1944 and headed for western Australia, concluding a disappointing 56-day patrol at Fremantle on 4 October.