USS Mertz (DD-691) was a Fletcher-class destroyer of the United States Navy. The designation DD-691 marked her as a destroyer, and she was built to the Fletcher design.
She was launched on 11 September 1943. Commissioning followed on 19 November 1943, a little more than two months after the launch, and on that day she entered service.
William Sears Estabrook Jr. was her captain from 19 November 1943. His command dates from the commissioning, and Mertz began her commissioned life under him.
On 25 October 1944, Mertz took part in the Battle of Surigao Strait. She was in the destroyer torpedo attack, the attack in which the destroyers used their torpedoes.
Mertz survived the war. The hull was sold for scrap on 16 December 1971. The destroyer launched in September 1943, and present in the torpedo attack at Surigao Strait, ended in that sale.