Jan Viljoen served in the Schoonspruit Ward of the Potchefstroom Commando. He saw service during the Siege of Mafeking and at the Battle of Magersfontein and was taken POW at Paardeberg on 27 February 1900 when Gen. Cronje and his force surrendered. He was sent to St. Helena (POW No 2976, age 24) and was repatriated on 4 September 1902.
An interesting speculation: could he be the J.A. Viljoen who is named as a ZAR Secret Service Agent in the 1999 Doctoral Thesis of H.J.G. Kamffer? A “start of service” date of 18 November 1899 is quoted for that Viljoen: could the Potchefstroom Viljoen have been recruited during the period of his Mafeking service?