They also had a test site in the Kalahari desert. The plan was to detonate a nuclear weapon within the territory of South Africa in case they where threatened by communist Angola, to show that they had and was serious about using nuclear weapons. The idea was that this would force Western powers to intervene on the side of South Africa, to avoid nuclear weapons being used against Angola.

There is a great book detailing the nuclear program in South Africa: https://www.amazon.com/South-Africas-Weapons-Mass-Destructio...