Six days later, she took Army artillery observers along the coast to Sarmi where she shelled enemy emplacements and an air strip.

She remained at Kossol Passage for a month, serving as harbor entrance control ship before returning to Hollandia.

Thomason headed for the Philippines on 9 November in the screen of a large convoy of landing craft and supply ships.

The destroyer escort then conducted intensive antiaircraft and antisubmarine training at Mios Woendi and landing exercises at Aitape with attack transports that were scheduled to participate in the invasion of Lingayen Gulf.

On 28 December 1944, the destroyer escort sortied for Luzon with Task Group 78.1 (TG 78.1), the San Fabian Attack Force.

At 22:22 on 7 February, Thomason's SL surface radar made a contact at a range of 14 miles (26 km), which was thought to be a small boat.

On both runs, a large submerged mass, outlined by phosphorescence, was seen moving through the water at a depth of between 25 and 50 feet.

The two ships patrolled until late in the morning, in an expanding search pattern, but never regained contact with the Japanese submarine.

From March through August, the ship was engaged in antisubmarine patrols and escort duty between various Philippine ports, Palau, and Hollandia.