Harold Holt was the Prime Minister of Australia from 1966 until his mysterious disappearance in December 1967. On December 17, he went swimming at Cheviot Beach near Portsea, Victoria, but failed to return. The absence of both body and evidence of an incident intensified speculation about his fate, leading to a massive search operation conducted by the Australian Navy and air force, along with volunteers and local authorities. The search spanned several days but ultimately yielded no results, leading to heightened public interest and various rumors regarding his disappearance.

On December 19, after days of search and speculation, the government held a press conference where it was announced that Holt was presumed dead, marking the first time in Australian history that a sitting Prime Minister was officially presumed dead following a disappearance. As Holt was a popular political leader and had a significant role in promoting Australia's liberal policies, this announcement had profound implications for both his party and the nation's political landscape. It resulted in the Liberal party leader's loss of confidence and authority amongst peers and constituents.

The aftermath of Holt's disappearance led to the election of John Gorton, who became the new Prime Minister after a party vote. The incident shook the political landscape, as it occurred during a turbulent time in Australian politics, characterized by social change and a move toward progressive policies. Holt’s legacy, particularly his advocacy for Australian involvement in the Vietnam War and his push for greater immigration, was firmly shaped by this tragic episode in his life.