During the 1956 Suez Crisis, Duchess operated as plane guard and escort to the British carrier force, and was the last ship to leave Port Said after the British-French invasion failed.

The ship was deployed to the Far East Strategic Reserve throughout the 1960s, and operated as an escort for the Vietnam War troopship Sydney on several occasions.

[2] The main armament of a Daring-class destroyer consisted of six QF 4.5-inch Mk I – V naval guns, arranged in three twin turrets, two located forward, the third aft.

[11] On 26 January, while alongside in Portland Harbour, a furnace explosion and oil fire in A boiler room killed a stoker and severely burned three others.

[11] At the end of May, Duchess, Daring, and Swiftsure sailed to London, where they participated in the opening celebrations of the coronation of Queen Elizabeth II.

[12] Duchess returned to Portsmouth in July, underwent six weeks of maintenance, then sailed on 1 September to rejoin Eagle and other ships for exercises in the Denmark Strait.

[12] The exercise ended on 3 October, and after transporting personnel of 812 Naval Air Squadron to Loch Goyle, Duchess joined Eagle while the latter undertook flying training.

[12] On 29 April, the destroyer departed for Gibraltar to meet the royal yacht Britannia, which was carrying Queen Elizabeth II on the final legs of her Commonwealth Tour.

[15] Resuming operations on 28 September, Duchess sailed to Scottish waters for exercises: first anti-submarine and torpedo firing training off Clyde, then plane guard duties near Rosyth while Eagle's aircraft practiced high-altitude intercepts.

[16] During the exercise, the naval correspondent for The Daily Telegraph was convinced by the officers to place a small article in the paper jokingly asking for "any spare coronets" to decorate the wardroom with.

[17] The Mediterranean Fleet began gearing up to retaliate, with Duchess undertaking shore bombardment and convoy escort training during August and September, and also serving as plane guard to Eagle as the carrier worked up.

[17] On 6 November, the joint British-French invasion commenced, with the destroyer escorting one of the landing craft groups into shore, then standing by off Port Said for anti-air and anti-submarine defence.

[17] From 27 November to 16 December, the destroyer was sent to Cyprus for more anti-smuggler patrols, but the ship was recalled to cover the final withdrawal of British forces from Port Said.

[18] After spending Christmas at Grand Harbour, Duchess sailed from Malta on 1 January 1957 with sister ships Decoy and Diamond, bound for Portsmouth.

[18] The destroyers were then assigned to escort the carrier Ark Royal, with the three ships departing on 30 May for the International Naval Review at Hampton Roads in the United States.

[21] Workups were conducted at Silema Creek during September, followed by port visits to Tripoli and Civitavecchia in October, then self-maintenance and day sails from Malta for the rest of the year.

[21] Work concluded in September, and Duchess spent the next three months undertaking exercises and port visits in British, Dutch, and French waters.

[21] Modifications during this period included the deletion of the aft torpedo launcher and its replacement with a deckhouse for additional accommodation, introduction of centralised messing arrangements, and fitting of air-conditioning to the operations room and sickbay.

[24] From April until July, she was involved in a program of anti-submarine warfare training and general exercises, interspersed with short maintenance periods.

[24] On 7 August, while en route, a port visit to Ajaccio was almost cancelled when a possible mutiny aboard a British merchant ship was reported: the destroyer was to sail to assist, but was not required.

[26] In addition to the schedule of Home Fleet exercises, Duchess made official visits to Stockholm and Helsinki with Bermuda in May, underwent refit from July to October, as in November was part of the search for the helicopter that crashed off St David's Head carrying Lord Windlesham.

[29] Further patrols of North Borneo occurred in October, and on 7 November, the destroyer was called to assist the British merchantman Woodburn, which had run aground off Singapore's Horsburgh Lighthouse.

[30][31] The Admiralty suggested Defender because she had just completed a major modernisation, and Duchess because her location in South East Asia meant she could be handed over quickly.

[33] In late May, Duchess was assigned to the escort screen for the troopship Sydney as she made her first of twenty-five Vietnam War troop transport runs to Vũng Tàu.

[32] After a short period of patrols, the destroyer and Vendetta were detached to meet Sydney off Manus Island on 20 December, and joined the troopship on her second voyage to Vietnam.

[32][35][36] 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.

[32] Official visits to ports in South Korea and Japan followed, with Duchess back in Hong Kong for the Christmas-New Year break.

[32] Maintenance and local exercises dominated the ship's schedule until November, when she headed north to escort Sydney on the latter's fifteenth voyage.

[42] Duchess sailed to Hong Kong, then on 8 June departed for Australia, arriving on 25 May and commencing a mid-cycle docking which ran until 13 November.

[32] From January 1975 to July 1976, Duchess operated on a sequence of training cruises, visiting ports along the eastern Australian coast, as well as New Zealand and the South Pacific.