From December 1942 to April 1943, James O'Hara served as an Army transport, steaming from the West Coast to Australia, thence via the Panama Canal to New York.

Despite heavy seas and an enemy air attack, she debarked her troops as Allied forces sought to wrestle the strategic island from Axis control.

During almost the next 2 months James O'Hara shuttled troops from North Africa to Sicily; then she prepared to take part in the Allied invasion of Italy.

Undaunted by German air attacks, the veteran transport discharged cargo at the Paestrum beaches before departing for Oran 11 September.

As part of Vice Admiral R. K. Turner's Northern Attack Force, she departed Pearl Harbor 29 May; touched at Eniwetok; and carrying troops of the 4th Marine Division, arrived off Saipan in the early hours of 15 June.

After embarking casualties and enemy prisoners, she departed 17 June and cruised northeast of Saipan while Vice Admiral Marc Mitscher's Fast Carrier Task Force defeated Admiral Ozawa's Mobile Fleet in the Battle of the Philippine Sea, the greatest carrier battle of the war.

Assigned to the Northern Attack Force, she entered Leyte Gulf 20 October, closed about 7 miles off San Ricardo and debarked five waves of assault troops.

As part of Vice Admiral D. E. Barbey's San Fabian Attack Force, James O'Hara departed Sansapor, New Guinea, 30 December with troops of the 6th Infantry Division embarked.

Departing the same day, she steamed via Leyte and Ulithi to Guam where she arrived 6 February to stage for the amphibious invasion of Iwo Jima.

After arriving 17 November, between 22 December and 4 February 1946 she made another Operation Magic Carpet run to Saipan and back to the West Coast.

During the struggle to repulse Communist aggression in South Korea, James O'Hara transported troops and supplies from the West Coast to the Far East.