 After the Battle of the Coral Sea, the area covered by the 4th Fleet was reduced to an “inner core” of Japanese possessions, while the new IJN 8th Fleet was assigned to confront the advancing American forces in the Solomon Islands and New Guinea.However, in November 1943, the Americans attacked the Gilbert Islands and captured the major naval base of Tarawa, which brought the 4th Fleet and its various garrison forces back into the front lines of combat.The Americans continued to advance through the Marshall Islands in early 1944, neutralizing the Japanese bastion at Truk Atoll in the Carolines, headquarters of the IJN 4th Fleet, by means of powerful naval air strikes in February, and forcing the removal of Japan's major naval units to Palau, which also proved vulnerable to air attack.