On 5 August, she commenced exercises at Adak and on the 15th anchored off Quisling Cove, Kiska, to take part in what was expected to be an assault on a Japanese stronghold.

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.

Discharging cargo on call, Thuban remained off Betio until 27 November, when she departed the Gilberts in company with Task Group (TG) 53.8 and headed for the Hawaiian Islands.

During "Operation Flintlock", Thuban's boats were constantly busy; and, because of the nature of the seas and the beaches, the landing craft took a beating, often requiring repairs after only two trips.

On 1 May, she departed San Francisco to rejoin the 5th Amphibious Force, encountered foul weather and mountainous seas during the passage to Hawaii, and arrived at Pearl Harbor on the 6th.

Ships of the screen reported the sinking of a submarine as Thuban steamed around the northern tip of the island and headed south, sighting Saipan for the first time at 0445.

As the first assault waves hit the beach in the faint light of early dawn, Thuban's crew enjoyed a grandstand view of "D-day" on Saipan, especially of the shoreline south of Charankanoa where her own landing craft were operating.

Anchored off Susupe Point on the morning of the 27th, Thuban embarked 91 injured men filling sick bay, the main deck, and many quarters areas to overflowing with stretcher cases.

Returning to Saipan on the 19th, she provided fuel, water, and ammunition to ships of the Marianas invasion force, took on empty brass, and repaired landing craft.

There, following amphibious exercises off Maui, she embarked Army troops; rendezvoused with TG 33.3; and headed via the Marshalls for the Admiralty Islands, arriving at Manus on 3 October.

In the early hours of "A-day," 20 October, the formation fought the strong currents of the Surigao Strait and drove off a Japanese dive bomber before arriving in the outer transport area.

Although interrupted by calls to general quarters and the necessity to make smoke when an air attack was imminent, for three days she discharged a steady stream of vital ammunition, engineering equipment, trucks, trailers, and rations for the troops on shore.

On the morning of the 21st, two enemy planes came in low, evading detection, and dropped bombs near the attack transport Custer (APA-40), 1,000 yards (900 m) astern of Thuban.

During this period, a number of aerial dogfights occurred in her area and, although Thuban was not attacked directly, she helped to repel enemy raiders on four occasions.

Thuban then joined Transport Division 7 during rehearsals for the impending Lingayen Gulf landings, embarked troops of the 43rd Artillery, and on 29 December 1944 departed New Guinea with Task Group 78.1, bound for the Philippines.

The passage was marked by the sighting of an enemy aerial snooper and the sinking of a Japanese midget submarine by destroyer Taylor (DD-468) south of Apo Island.

During a twilight air alert that day, enemy attackers dropped bombs nearby, and Thuban fired on a Japanese fighter plane.

After loading elements of the Army's 41st Division, she departed New Guinea on 2 February, paused briefly in Leyte Gulf, and arrived off Mindoro Island on the morning of the 9th.

Arriving at a point 70 miles (110 km) southeast of Iwo Jima in company with TG 12.6 on 9 March, she remained there until the morning of the 17th when she proceeded to the hard-won island and embarked tired, battered, but victorious Marine units.

She stopped at Ulithi on 4 August, rendezvoused with elements of Service Squadron 6 on the 8th, and throughout that month provisioned ships of the 3rd Fleet off the coast of Honshū as they awaited the occupation of Japan.

After the formal surrender ceremony in Tokyo Bay, she continued to supply American ships, visiting anchorages on the Korean and China coasts into the new year.

Transferred to the Naval Transportation Service early in 1946, she operated between the west coast of the United States and various Pacific island groups, including the Marianas and Japan, participating in occupation duties until the outbreak of the Korean War in the summer of 1950.

After combat loading and embarking Army and Navy personnel, Thuban proceeded to Kobe and, on 11 September 1950, got underway with TG 90.2 bound for Operation "Chromite" – the assault on Inchon.

Throughout the 1950s, she continued the familiar round of east coast and Caribbean ports, varied by a voyage to Japan in 1953 and by participation in various fleet exercises in the Atlantic.

Increasing tension in the Middle East exploded into war on 30 October, and Thuban was called upon to evacuate American nationals from Egypt early in November.