"Thresher" later surfaced at 23:00 and proceeded on a course which took her north to Pearl Bank. There, in the northernmost reaches of the Gulf of Siam, she made one of the first mine plants by a submarine in the Pacific War. These strategic mine fields laid by "Thresher" and her sisters in subsequent patrols, covered Japanese shipping lanes in areas of the Southwest Pacific Command previously unpatrolled by submarines. Later, these minefields filled the gap between patrol zones along the coastal waters of Malaya, Siam, and Indochina, when many boats were diverted to participate in the Solomon Islands campaign.