This was followed by a series of similar operations, shepherding convoys between U. S. ports and: Casablanca, French Morocco; Bizerte, Tunisia; and Belfast, Northern Ireland.

Arriving in the forward area in December, she joined the 3rd Fleet under Admiral Halsey, and took part in the operations which culminated in the reconquest of Luzon in the Philippines.

In February 1945, O'Neill became a unit of the 5th Fleet under Admiral Spruance, and served as an escort for the transports which landed the 3rd Marine Division at Iwo Jima.

In the prolonged fight for the island, she served almost continuously for 60 days on ASW picket duty – shooting down a Japanese twin-engined bomber on 25 May, and being hit by a kamikaze suicide plane on the 26th.

O'Neill was placed out of commission in reserve on 2 May 1946, and berthed at Green Cove Springs, Florida, until 23 October 1950, at which time she was transferred to the Netherlands under the Mutual Defense Assistance Program.