Peleliu and Angaur Mertz participated in the occupations of Peleliu and of Angaur in the Palau Islands, arriving 10 September. She retired to Manus, Admiralty Islands, on 23 September to prepare for the invasion of Leyte, Philippines. Philippines campaign On 20 October, D-Day for the Leyte landing forces, Mertz escorted landing craft through air attacks to the beach and later in the day patrolled off Dinagat Island at the entrance to Leyte Gulf. Early in the morning of 25 October as the Japanese Southern Force approached Leyte Gulf through the Mindanao Sea, Mertz and patrolled between Desolation Point and Homonhon Island, lest the enemy fleet choose to steam north along the east coast of Dinagat Island to attack the Allied beachhead. When the Japanese entered Surigao Strait, Rear Admiral Jesse B. Oldendorf’s force met and destroyed the enemy armada in the classic “crossing-of-the-T” maneuver known as the Battle of Surigao Strait, part of the overall Battle of Leyte Gulf. Later that same day Mertz splashed a Zero at several hundred yards with heavy machinegun fire. With the Leyte beachhead established, the destroyer got underway 26 October for Hollandia, New Guinea, anchoring in Humboldt Bay on the 30th to replenish. She got underway for Leyte again 9 November escorting a reinforcement convoy arriving 5 days later. Mertz then continued on to Seeadler Harbor, Manus, to join a task unit staging for the daring expedition through the Sulu Sea, controlled by the enemy since early 1942, to capture Mindoro. The American ships had to contend with both a typhoon and heavy air attacks. Mertz splashed a Ki-43 ("Oscar") 15 December and assisted in the destruction of several others. Departing San Pedro Bay 4 January 1945, she made another voyage through the Sulu Sea, to support the invasion of Luzon at Lingayen Gulf on 9 January before returning to San Pedro Bay on 16 January. Attacks on Japan On 10 February, Mertz steamed from Ulithi for three months at sea with the Fast Carrier Task Force. During this time, she played a role in the airstrikes on the Tokyo area 16 February, the landings on Iwo Jima 19 February, and the raids on Okinawa 1 March. While screening the flattops off Kyūshū, Japan, in March, she downed two more enemy planes. While operating off Okinawa Mertz helped sink the on 18 April. The destroyer retired to Ulithi 14 May, before returning to Okinawa