As one of the ship's final duties with the Navy, "Australia" was tasked with transporting Field Marshal Sir William Slim, the Governor-General of Australia, along with his wife and their staff on a cruise around the Coral Sea, the Great Barrier Reef and the Whitsunday Passage. The voyage embarked on 4 May, and two days later "Australia" fired its 8-inch guns for the final time. While in the Coral Sea, a Dutch naval ship was discovered to be incapacitated off the coast of Hollandia, Netherlands New Guinea, and was consequently towed by "Australia" to Cairns. McNicoll was later appointed a Commander of the Order of Orange-Nassau by the Dutch government for his rescue of the ship. McNicoll relinquished command of HMAS "Australia" in July 1954 before the cruiser was paid off and marked for disposal the following month, and he briefly returned to duties at the Navy Office. In November, he embarked for London to attend the Imperial Defence College as part of the 1955 course intake, which signified that he had been marked for senior command. McNicoll and his wife, Ruth, had separated in 1950 and their divorce, which cited adultery as the cause, was finalised in October 1956, while the former was still in London. On 17 May the following year, McNicoll wed Frances Mary Chadwick, a journalist, in the Hampstead register office. Made acting rear admiral in January 1957, McNicoll was appointed as Head of the Australian Joint Service Staff in London. He returned to Australia in February 1958 and was selected to serve as Deputy Secretary (Military) at the Department of Defence; McNicoll's rank was made substantive in July that year. On 8 January 1960, McNicoll was posted to the Naval Board in Canberra as Second Naval Member and Chief of Personnel. As noted by historian Ian Pfennigwerth, McNicoll held this position at a time in which recruitment and retention in the Navy particularly lagged behind targets. McNicoll was additionally appointed as a trustee of the RAN Relief Trust Fund during this period. Completing his term on the Naval Board, McNicoll was posted as Flag Officer Commanding HM Australian Fleet on 8 January 1962 and hoisted his standard aboard , the flagship of the RAN. The Australian government had designated the role of the RAN to be primarily one of anti-submarine warfare, a posture which McNicoll thought unwise. McNicoll argued that surface and air weapons posed a threat equal to that of submarines toward vessels in modern naval warfare.