Following shakedown in the Chesapeake Bay, Appalachian headed south; transited the Panama Canal; and reached San Diego, California, on 26 November 1943.

There, after elements of the 4th Marine Division had embarked, and Rear Admiral Richard L. Conolly had broken his flag in Appalachian, she got underway on 13 January 1944, bound for Hawaii.

The attack opened on 31 January; and the next day, Appalachian entered Kwajalein lagoon and began disembarking the men and equipment of the headquarters battalion of the 4th Marine Division.

Appalachian returned to Guadalcanal in late April, spent the next six weeks preparing for the impending assault on the Marianas, then, early in June, sailed to Kwajalein, the final staging area for the operation.

On 12 June, Appalachian with Major General Roy S. Geiger, USMC, embarked, sortied in a group of transports carrying troops of his III Amphibious Corps.

When the force had progressed to within 50 miles of its objective, it was ordered to reverse course to avoid a powerful Japanese fleet which was then approaching the Marianas to contest the American landings.

After her troops had gone ashore, the ship stood by to supply provisions and freshwater to smaller craft in the area until the 23rd, then headed for New Guinea, and arrived in Humboldt Bay five days later.

Appalachian sailed for the Solomons on 17 December, engaged briefly in invasion rehearsals at Guadalcanal, and stood out to sea on Christmas Day bound for Manus.

Appalachian sailed east on 18 January and made port calls at Ulithi and Pearl Harbor before reaching San Francisco, Calif., on 13 February.

The ship set out for occupation duty in Japan on 18 September, arrived at Aomori at the northern end of Honshū on the 25th, and landed troops who took possession of the town.

After reaching the United States, she remained at San Francisco until 12 April 1946[citation needed] when she was assigned to Joint Task Force 1 which was being established for Operation Crossroads, the atomic bomb tests to be carried out that summer at Bikini Atoll.