5 October 1960
The South African government led by National Party (NP) held a referendum in which white voters  decided whether South Africa should remain a member of the British Commonwealth of Nations or declare  a republic. The voting age restriction was lowered to eighteen years and included the white voters in South West Africa (now Namibia). The two former Boer republics, Transvaal and Orange Free State (now Free State), and South West Africa, voted in favour, while the Cape Province, though also in favour, had a smaller majority. Natal (now kwaZulu Natal), which was inhabited by more English-speaking whites than Afrikaners, voted against it. The opposition United Party (UP) actively campaigned for a 'No' vote, while the smaller Progressive Party appealed to supporters of the proposed change to 'reject the republic', arguing that South Africa's membership of the Commonwealth, with which it had privileged trade links, would be threatened. The result was 52 per cent in favour of a republic. Further reading: on SA becoming a Republic.
References

Saskatoon Star-Phoenix,(1960), ‘Secession Talk By Some Anti-Republicans’, in 11 October, [online], Available at news.google.com (Accessed: 4 October 2013)|Muller, C.F.J. (ed)(1981). Five Hundred years: a history of South Africa; 3rd rev. ed., Pretoria: Academica, p. 507.