McCampbell formed Fighter Squadron 15 (VF-15) on September 1, 1943 and led the squadron before being reassigned as Commander of Air Group 15 (CAG-15) in February 1944 to September 1944. As Commander, Carrier Air Group (CAG) 15, he was Commander of the "Essex" Air Group (fighters, bombers, and torpedo bombers) when the group was aboard the aircraft carrier . From April to November 1944, his group saw six months of combat and participated in two major air-sea battles, the First and Second Battles of the Philippine Sea. During the more than 20,000 hours of air combat operations before it returned to the United States for a rest period, Air Group 15 destroyed more enemy planes (315 airborne and 348 on the ground) and sank more enemy shipping than any other Air Group in the Pacific War. Air Group 15's attacks on the Japanese in the Marianas and at Iwo Jima, Taiwan, and Okinawa were key to the success of the "island hopping" campaign.