Between 5 December 1943 and 13 February 1944 "Sumner" participated in the occupation of Tarawa and conducted a survey of the newly acquired area. She sailed to Kwajalein in February 1944 where she was engaged in improving the harbor facilities until 11 April. The ship then stood out for San Francisco, via Pearl Harbor, arriving 7 May. Repairs completed, "Sumner" returned to the Hawaiian Islands in August. In September she steamed to Ulithi where until February 1945 she conducted survey operations. On 1 February she sailed for Guam where she remained until 27 February. On 4 March she arrived at Iwo Jima and commenced surveying operations under very adverse conditions. On 8 March she was hit by an enemy shell which killed one of her crew and injured three others. The shell failed to explode and material damage was light. "Sumner" continued surveying the area until 3 May when she departed for Guam. She remained at Guam until 17 June when she sailed to Leyte Gulf, Philippine Islands.