"Sigourney" then made escort trips between Guadalcanal, Cape Gloucester, Purvis Bay, Majuro, Eniwetok and Kwajalein. On 11 May, the destroyer sortied from Kwajalein with Task Group 51.18 (TG 51.18), the Joint Expeditionary Force, Reserve, for the amphibious assault on Saipan and Tinian in the Mariana Islands. "Sigourney" arrived off Saipan, on 16 June, and participated in operations there and on Tinian until she withdrew from the operations area on 20 August. During her time on station, she bombarded beaches on both islands, supplied call-fire support for the forces ashore, and served as a picket ship and as an antisubmarine screen.