For the first part of her second patrol, "Piranha" joined 9 other submarines in offensive reconnaissance covering the Third Fleet during the assault on Peleliu, patrolling 30 August to 25 September. When Peleliu, deemed essential for the liberation of the Philippines, had been seized, "Piranha"’s group dissolved and she searched for targets westward along the 20th parallel, engaging an enemy patrol craft 9 October. She endured a heavy depth charge attack, but outsmarted the patrol vessel, returning to Pearl Harbor 23 October.