Now "Chauncey" was assigned to guard the escort carriers assembling and rehearsing for the Marianas operation, and on 8 June 1944, arrived at Kwajalein for final preparations. She got underway two days later to screen carriers supporting the landings on Saipan with preassault raids on 13 and 14 June, and air cover during the assault on 15 June. Next day "Chauncey" joined the group operating off Guam for bombardments and air strikes, and her guns aided in driving off enemy air attacks on the 16th and 17th. Returning to Saipan, she screened carriers there until the 25th, when she got underway to escort transports to Eniwetok. She returned to operate with the carriers off Saipan and Guam from early July, and on 9 July began her part in the continuous bombardment of Guam before the landings there 21 July.