Next on the timetable of conquest in Micronesia were the Marianas, and "Harrison" sailed 4 June for the Marshalls to prepare for that operation. Arriving Kwajalein 8 June, she engaged in patrolling and readiness operations until 17 June, when she sailed for Guam. "Harrison" arrived 21 July and lent fire support to Marines ashore in addition to patrolling the transport areas. This operation not only constituted a break in Japan's inner ring of defenses, but dealt a death blow to the Empire's naval air arm at the Battle of the Philippine Sea. "Harrison" sailed back to Espiritu Santo via Eniwetok 16 August.