"Lipan" departed Guadalcanal on 4 June with Rear Admiral Reifsnider's Southern Transport Attack Group for the scheduled assault on Guam. When the invasion of Guam was postponed by the Battle of the Philippine Sea, the ship joined Service Squadron 10 at Eniwetok on 3 July supporting the invasion of Saipan. Departing on 8 July with barge in tow, she arrived at Saipan on 15 July and remained under constant enemy fire until 20 July, then rejoined Admiral Reifsnider's group at Agat Bay, Guam, on D-Day, 21 July. During the two weeks of fierce fighting after D-Day, "Lipan" rescued landing craft grounded by the treacherous surf ringing Agat Bay. Once the U.S. Marines had gained a foothold, the tug towed supply ships bringing in reinforcements to liberate the island and transform Guam into an advanced base for the Philippine campaign.