Robyn Thorn grew up in the rural town of Kingaroy in Queensland, Australia. After breaking her arm after falling from a pony, Thorn began swimming as part of her rehabilitation, eventually being selected to represent her country at the British Empire and Commonwealth Games whilst still only 17-years-old. At her home Games in Perth in 1962 she won gold in the 4 × 110 yards freestyle with compatriots Dawn Fraser, Lyn Bell, and Ruth Everuss. Thorn also won silver in the 110 yards freestyle in Perth, finishing second to Fraser. Two years later she was part of the Australian team that won silver in the 4 × 100 metres freestyle relay at the Tokyo Olympics. Thorn retired from swimming shortly after the Olympics, later getting married and having four daughters.
AUS