On 13 June 1944 the Combined Fleet activated Operation A-Go for the defense of the Mariana Islands, and the Battle of Saipan began with U.S. landings on Saipan on 15 June 1944. On 5 July 1944, "Ro-48" departed Kure, Japan, to begin her first war patrol, assigned a patrol area in the Marianas off Saipan. She arrived in her patrol area, within of Saipan, on 12 July 1944, and that date received orders to stand by to rescue Imperial Japanese Navy Air Service pilots stranded on Tinian. While she was north of Saipan at 21:30 Japan Standard Time on 14 July 1944, her commanding officer reported U.S. forces had forced him to submerge and that he was moving to a new position. On 16 July 1944, 6th Fleet headquarters ordered "Ro-48" to return to Japan.