During this first American land offensive of the war, Fomalhaut lay anchored in such a position as to observe the Battle of Savo Island 9 August, and that day sailed for Noumea to load additional men and supplies for Guadalcanal.

As two other destroyers sank Blue to prevent her from possibly falling into enemy hands, Fomalhaut was ordered underway with all but a quarter of her cargo unloaded.

Through one year and a half, Fomalhaut carried out continuous cargo operations in the southwest Pacific, going through some of the hottest fighting of the war supporting the many landings and shore campaigns in the battle for Guadalcanal and the other islands of the southern Solomons.

After tests and training along the Maine coast, Fomalhaut arrived at Norfolk 7 November 1944 for conversion to an underway ammunition replenishment ship, and in her new role she reported for duty at Ulithi 10 January 1945.

Aside from the period 19 to 28 February, when she was at San Pedro Bay, Leyte, arming amphibious ships for future operations, Fomalhaut sailed out of Ulithi to deliver ammunition at sea to combatants and their auxiliaries.