Fifty-five years ago today, December 18, 1967, Australia experienced a singular event. For the only time since Federation in 1901, a whole day passed without a prime minister in office.

The day before, December 17, prime minister Harold Holt disappeared in the sea off Cheviot Beach, in Portsea, Victoria. On December 18, a search for his body was continuing, but little hope was held for its recovery. It was not until December 19 that Holt’s successor, John McEwen, was sworn in as prime minister.

Dec 18, 1967: Country Party leader John McEwen, ahead of his appointment as prime minister the next day.

Constitutional convention requires that there must always be a prime minister to advise the Governor-General. Two previous prime ministerial deaths in office were followed by same day or next day appointments of a new prime minister.

Prime ministerial resignations following retirement, party leadership challenges or electoral defeat always take place at the precise moment the new prime minister is sworn in. In this way, continuity prevails.

In 1967, Christmas was only a week away. Parliament had adjourned for the year. Politicians had left Canberra. Holt disappeared on a Sunday. Speedy appointment of a new PM was difficult.

An important complication arose because there was no such office as Deputy Prime Minister at that time. Who was the deputy to the prime minister? The deputy leader of the Liberal Party? The leader of the junior coalition party?

Ultimately, the decision about who to appoint had to be made by the Governor-General. Lord Casey, formerly Richard Casey, was a former long-time Liberal Party politician. He served as Treasurer for three and a half years under Lyons in the 1930s. In 1940, he was Minister to the United States, effectively ambassador. In 1944, he was appointed Governor of Bengal. In 1949, he returned to the Commonwealth Parliament as the Liberal member for La Trobe, a new seat in Melbourne’s outer east. Until 1960, he held portfolios in the Menzies government, including ten years as Minister for External Affairs, now called Foreign Affairs. In 1965, Menzies appointed him Governor-General.

Casey’s decision on Holt’s successor was informed by his understanding of politics, the Liberal Party and the coalition relationship. He had served alongside all the key players in the Liberal-Country Party coalition government since 1949.

Two days after Holt’s disappearance, on December 19, the Country Party leader, John McEwen, was sworn in as Australia’s 18th prime minister.

Dec 19, 1967: John McEwen is sworn in as PM by G-G Lord Casey.

McEwen’s appointment by Casey was in accordance with the precedent established in 1939, following the death of PM Joseph Lyons on April 7. The Country Party leader, Earle Page, was appointed prime minister the same day. As the leader of the junior coalition partner, he was deemed appropriate as a temporary stand-in.

Page held office over 20 days, from April 7 until April 26, 1939. He relinquished office to the newly-elected leader of the United Australia Party, Robert Menzies.

When Labor prime minister John Curtin died in office in 1945, the choice of replacement was much easier. The deputy leader of the ALP, Frank Forde, was sworn in the next day. He served as PM over 8 days from July 6 until July 13, when he relinquished the prime ministership to the new ALP leader, Ben Chifley.

McEwen held office over 23 days as prime minister from December 19, 1967 until January 10, 1968, when he relinquished the post to the new Liberal Party leader, Senator John Gorton. Gorton subsequently won the by-election for Holt’s Melbourne electorate of Higgins and moved to the lower house. He is the only senator to have ever served as prime minister.

In 1968, the position of Deputy Prime Minister was officially created. John McEwen was the first person to hold the title, even though it had been used unofficially for many years.

Upon taking office in 1967, McEwen paid tribute to Holt. The official statement is shown below: