Before dawn on "D-Day," 20 November 1943, "Thuban" arrived at her assigned position in the transport area off Betio Island and began lowering boats and "amph-tracs" for the initial assault on Tarawa. All of her boats were in the water by 0435, and "Thuban" prepared to unload cargo. At 0551, as she maneuvered to maintain her station in the transport area, enemy shore batteries found the range of the transports, and a shell landed between "Thuban" and attack transport . The transports quickly headed out to sea, beyond range of the shore batteries, but not before additional shells landed among them, providing many anxious moments.