It was suggested Harold Holt disappeared on a Chinese submarine but the former prime minister's grandson reckons that story is "madness", noting his grandfather didn't even like Chinese food.
Holt went for a swim at Victoria's Cheviot Beach 50 years ago on December 17, 1967 and was never seen again.
It's believed he drowned but the 59-year-old's body was never recovered and conspiracy theories swirled, including a wild allegation he was a Chinese spy and was secreted away on a submarine.
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But grandson Robert Holt says Cheviot Beach was too shallow for such a vessel to get in, and in any case his grandfather wasn't a fan of Chinese cuisine.
"Every year there are people who drown in Australian waters and we never find the body," Robert told Channel Nine on the 50th anniversary of Holt's disappearance.
"If you look at the beach here and how shallow it is, the idea that a submarine could have got in here is absolute madness.
"My grandmother said he didn't even like Chinese food. So it's unlikely (he was) taken away by a Chinese submarine."
Robert hoped his grandfather, who was the political heir to Robert Menzies, would be remembered for his achievements rather than the way he vanished.
Holt oversaw the dismantling of the White Australia policy and drove the historic referendum to ensure Aboriginal people were included in the census.
"He was very progressive in his thinking," Robert said at Cheviot Beach.
"So we are very keen that he is remembered for his achievements, not just the last few minutes of his passing."
A memorial service will be held for Mr Holt at the former barracks near Point Nepean on Sunday, the 50th anniversary of his disappearance, with tributes expected from Flinders member Greg Hunt and federal Speaker Tony Smith.
Malcolm Turnbull earlier this month led tributes in Canberra's lower house, calling Holt's disappearance one of the most "confounding" events in the country's history.
"He ushered in many of the reforms that we now consider so crucial, such watersheds in our evolution to the modern nation that we are today," Mr Turnbull said.
Holt also introduced dollar currency and the child endowment scheme, which was the first time mothers were paid a benefit for raising children.
He also ramped up Australia's commitment to the Vietnam War and some conspiracy theories about Holt's disappearance have been linked to his war leadership.
