From Festipedia, hosted by the FR Heritage Group
For more detail see NG15 on Wikipedia.

The NG15 class of locomotives were developed for use on the 60 cm gauge lines of South African Railways and were a development of previous classes of locomotive.

The origin of the design was the three locomotives of the Hd class built for the Otavi Railway in German South West Africa (now Namibia). Needless to say these locomotives were German built being constructed by Henschel & Sohn in Kassel. The design progressed in 1922 with a further six locomotives, again built by Henschel & Sohn, that became the NG5 class.

After trials of one of the locomotives on the Avontuur line the design was altered again to become what is now known as the NG15 class. The preceding classes made use of flangeless driving wheels on one set of the eight coupled driving wheels, however this still proved unsuitable for the tighter curves on the Avontuur line. Therefore what differentiated the NG15s from their preceding classes was the use of a Krauss-Helmholtz pony truck for the leading wheels. This system allows the front driving axle some sideways movement so that only the rear three axles form a rigid wheelbase. The front axle is guided around curves by the front pony truck to which it is attached via a pivoted linkage. In spite of its size and weight, the class is remarkable for its axle load of less than 7 tons.

NG15s on the WHR[edit]

Three NG15s have been associated with the various incarnations of the Welsh Highland Railway

See also[edit]