On 1 March 1967, the ensign flown by RAN ships was changed from the British White Ensign to the Australian White Ensign. "Sydney" became one of only two RAN ships to undergo wartime service under both ensigns—the other being —and the only RAN ship to fly two ensigns during the same conflict. With 7 RAR embarked, "Sydney" departed her namesake city on 8 April for her fifth voyage to Vietnam. With "Vampire" escorting and Westland Wessex helicopters aboard for the first time, the troopship spent 20 April disembarking 7 RAR in Vũng Tàu before arriving in Singapore two days later. On 28 April, the two ships left Singapore on the sixth voyage, to collect 5 RAR. The battalion was embarked on 30 April, with "Sydney" arriving home on 12 May. Although the fifth and six voyages are officially recorded separately, they are sometimes counted as a single trip, because "Sydney" did not return to Australia in between.