She continued to patrol the Truk area until 20 September, when she decided to leave the southwest part of the patrol area and explore south of the Namonuito Atoll. Under a bright moon and clear sky, the submarine sighted a freighter and her escort. "Wahoo" fired three torpedoes; all missed. A fourth hit the target, which was thought to take a port list and settled by the stern. Four minutes later, a series of three underwater explosions wracked the freighter. "Wahoo" was chased by the escort but escaped by radically changing course in a rain squall. Though credited at the time with a freighter of , postwar analysis of Japanese shipping records by JANAC showed no sinking at this time or place.