Morton, smarting from that last luckless patrol, asked to return to the Sea of Japan, and permission was granted. He elected to take a full load of the newly arrived Mark 18 electric torpedo rather than take the risk that further production runs of the Mark 14 steam torpedoes might still be defective. "Wahoo" got underway from Pearl Harbor, topped off fuel and supplies at Midway on 13 September, and headed for La Perouse Strait. The plan was to enter the Sea of Japan first, on or about 20 September, with following by a few days. At sunset on 21 October, "Wahoo" was supposed to leave her assigned area, south of the 43rd parallel, and head for home. She was instructed to report by radio after she passed through the Kurils. Nothing further was ever heard from "Wahoo".