She served again during World War I in the dangerous North Atlantic Ocean, delivering general goods and ammunition to American Expeditionary Force troops in Europe.

On 12 October, she cleared New York to round Cape Horn on the long route to the Asiatic Station, arriving at Cavite, Philippine Islands, 30 March, for service as storeship.

Supporting the quelling of the Philippine–American War, Celtic carried stores and passengers between the Philippines and Australian ports until 16 July 1903, when she weighed anchor for Puget Sound Navy Yard.

At the suggestion of her commander, President Roosevelt ordered the Celtic to earthquake-damaged Sicily because she was already full of Christmas provisions, where she set up a tent city at Messina.

She cruised the west coast carrying and issuing stores to the Fleet until 22 March 1921, when she was assigned to duty as cold storage station ship at Apra, Guam.