"Newcomb" shook down in the West Indies for a month, then made passage to the Marshall Islands, arriving 4 April 1944 for two months duty on antisubmarine patrol off the Japanese held Mille, Wotje, and Jaluit atolls. She next joined the assault on Saipan as flagship for the screen from 29 May until 5 August, serving as fire support and patrol ship at both Saipan and Tinian. On 22 June, while guarding transports, she and sank Japanese submarine , and on 4 July her well-directed fire broke up a Japanese banzai attack north of Garapan on Saipan.