The SAC was raised during the Boer War, and, in spite of their name, they functioned as mounted infantry, hence the use of 'Trooper' for the lowest rank. Even in peacetime in South Africa, there was a need for mounted police, and many of the SAC men deployed in the Orange Free State and Transvaal were mounted. The same applied to the police in the Cape Colony and Natal, and the tradition of using 'Trooper' continued. In the case of Natal, 'Constable' referred to policemen employed in court duties, and their rank was equivalent to that of Sergeant in other branches of the force.
Brett