Twelve days later, she departed on her fourth war patrol. Moving westward, she hunted in the Japanese traffic lanes between Kiska and Attu during the first week of the patrol. On 28 July, leaks developed in the after trim tank, but were compensated for by placing nine tons of water in the forward trim tanks. Although this meant that space was left to accommodate water for only one torpedo reload, depth control was regained, and with fuel suction shifted forward, reload capability slowly improved. On 29 August, she was off Amchitka to check for enemy shipping in sheltered areas on that island's north coast; then, on 31 August, she headed east to cover the Allied occupation of Adak. On 14 September, she returned to the junction of Rat Island and Amchitka where she continued her patrol for another six days. On 20 September, she headed for Dutch Harbor.