At some point, Australians stopped grieving Harold Holt’s death and many started to laugh about it instead. The sudden disappearance of a prime minister at a Victorian beach in December 1967 has furnished many wisecracks and memes. Former Cronulla Sharks coach Jack Gibson famously said that waiting for the team to win was like “leaving a porch light on for Harold Holt”.

The Harold Holt Memorial Swimming Pool in Malvern, commemorated in his honour in 1969, attracts its fair share of mirth. So do the conspiracy theories, deeply unserious as they are, of “double agent” Holt’s abduction by a Chinese submarine. A few years ago, Holt’s grandson pointed out that Cheviot beach was “too shallow for such a vessel”, and the late prime minister “wasn’t a fan of Chinese cuisine” anyway.

For all its comic potential today, Harold Holt’s disappearance was no joke at the time.

Holt had not enjoyed 1967. The war in Vietnam – effectively his war – was increasingly divisive. Old questions about the HMAS Voyager disaster in 1964 had caused political mayhem for him in parliament. Another scandal, this one about the misuse of VIP flights, had damaged his standing and that of his government.

In the final weeks of Holt’s life, he had faced off against his deputy prime minister, Country Party leader John McEwen, over Australia’s decision not to devalue the dollar in line with Britain’s devaluation of sterling. The exchange rate affected primary and secondary producers and was politically controversial enough to almost split the Liberal-Country Party Coalition.

There were personal challenges, too. Holt’s brother Cliff died in March, and by December the prime minister was suffering with shoulder and back pains. On Saturday December 16, the front page of The Australian reported that Holt’s doctor had advised him to “swim less”.

The prime minister was a man who thrived on physical risk and loved the water, so he ignored the advice. On Sunday morning he and a few companions, including lover Marjorie Gillespie and friend Alan Stewart, went to Portsea to catch a glimpse of the world-famous sailor Alec Rose’s yacht.

They then went to Cheviot beach,........

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