On 3 September, "Duchess" left Portsmouth to join the Mediterranean Fleet as leader of the 5th Destroyer Squadron. 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. 1958 commenced with a seven-week Cyprus patrol. By the end of the patrol on 21 February, the destroyer had developed a leak in her hull, but was able to reach Malta without difficulty. March consisted of participation in Exercise Marjex, followed by port visits to Taranto and Ancona, joint exercises with the Italian Navy, and a visit to Venice before returning to Malta. Major fleet exercises occurred in April and early May. "Duchess" was due to return to the United Kingdom in May, but unrest in Lebanon (which would escalate into the 1958 Lebanon crisis) required the destroyer to join a response force off Cyprus, which she remained with until 4 July. The destroyer sailed to Malta, then Portsmouth, and was docked for maintenance after arriving on 11 July. Work concluded in September, and "Duchess" spent the next three months undertaking exercises and port visits in British, Dutch, and French waters. The destroyer reached Spithead on 9 December, and was paid off into reserve later that day. The destroyer was taken into Portsmouth Dockyard hands for a two-year refit. 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. Intentions at the time were to install a Sea Cat missile launcher on the roof of the new deckhouse during a later refit, but in 1964, the decision was made to fit the launcher to new-build ships only.