From January to March 1965, "Duchess" was deployed to the Far East, and undertook numerous patrols of the Malaysian and Borneo coasts. In late May, "Duchess" was assigned to the escort screen for the troopship as she made her first of twenty-five Vietnam War troop transport runs to Vũng Tàu. "Duchess" escorted the former carrier for the entire voyage, with the two ships returning to Sydney on 5 July. After a maintenance period, "Duchess" was deployed to the Far East Strategic Reserve (FESR) on 11 August. After a short period of patrols, the destroyer and were detached to meet "Sydney" off Manus Island on 20 December, and joined the troopship on her second voyage to Vietnam. The three ships reached Vũng Tàu on 28 September, and departed two days later: after clearing the Market Time area, the two destroyers broke off and headed for Hong Kong. A brief period of maintenance concluded on 26 October, and "Duchess" resumed patrols until the end of the year. 1966 commenced with more Borneo patrols and a stint at guardship at Tawau. The destroyer returned to Darwin on 2 March, then sailed to Sydney for a seven-month refit. The rest of the year was spent exercising in eastern Australian waters.