In June 1921, the South African Railways placed a single experimental Class GB Garratt articulated steam locomotive with a 2-6-2+2-6-2 Double Prairie type wheel arrangement in service.

The main differences between these locomotives and the original were revised boiler proportions and a larger water bunker capacity.

It proved to be a successful locomotive, having good riding qualities and flexibility on light track with poor ballasting and many curves of 300 feet (91 metres) radius.

[1][2] A couple of the second batch of locomotives joined the first one on the South Coast line for a brief period, but most went directly to the Eastern Cape where they were used on the Port Alfred branch and the Aliwal North to Barkly East line, famous for its reverses and its 1 in 30 (3⅓%) compensated ruling gradients.

The Natal locomotives were soon also relocated to work there when the Class GC Garratts replaced them on the South Coast line later in 1924.