"Sumter" stood out of San Diego on 13 January 1944 en route to Lahaina Roads, Hawaii, to rendezvous with other units of Task Force (TF) 53, the Northern Attack Force for the Marshall Islands operation. She arrived there on 21 January and the force sortied the next day. "Sumter" and three other transports landed three battalion landing teams of the 25th Marines on the atolls of Ennumennet and Ennubirr on 31 January to establish field artillery positions in support of the main landings at Roi and Namur.