The mission of the fast carrier forces had by this time evolved into sealing off designated enemy-held atolls and islands which the Allies intended to take and interdicting others to isolate and keep to a minimum Japanese resistance at the target. Now a third mission was to be added, the pounding of major enemy bases without the aid of land-based aircraft, leaving little or no need for a return visit. Thus, to ease the occupation of Eniwetok and to aid in the encirclement of Rabaul, TF 58 departed Majuro and sailed for the Carolines. On 16–17 February, they devastated Truk, the best fleet anchorage in the Mandated Territories, the base of the Japanese combined fleet and the center for air and sea communications between Japan and the Bismarck Archipelago. The force then sailed northwest to the Mariana Islands for strikes on Saipan, Tinian, and Guam, encountering heavy aerial resistance there on 21–22 February. After a brief respite for replenishment at Majuro, "Mobile" sailed to Espiritu Santo, where the ships of TG 58.1 were reorganized as TG 36.1 on 12 March. On 15 March, they steamed northwest to cover Marine forces as they landed on Emirau on 20 March.