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The NG15 class of locomotives were developed for use on the 60cm gauge lines of South African Railways (SAR) and were an enhancement of an earlier design of 1922 that were designated NG5.
Initially the design started out as 3 locomotives of the Hd class for the Otavi Railway in what is now Namibia but at the time was German South West Africa. Needless to say these locomotives were German built being constructed by Henschel & Sohn in Kassel. The design progressed in 1922 with a further 6 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 we now know 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.
The distinctive
feature therefore, that differentiated the NG15s from their preceding
classes was the use of the Krauss-Helmholtz pony truck for
the leading wheels. This system allows the front driving axle
some sideways movement so as 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.
The following pictures show the bogie and pivot after removal from 134
in
January 2009.
In total 21
locomotives of the NG15 class were built in 5 Lots between 1931 and
1957 with construction shared between Henschel & Sohn in
Germany and
Societe Anglo-Franco-Belge in Belgium
. See table below.
| Year | Quantity | Builder | Builder's №s | SAR №s |
| 1931 | 3 | Henschel & Sohn | 21905 - 21907 |
17 - 19 |
| 1934 | 3 | Henschel & Sohn | 24475 - 24477 | 117 - 119 |
| 1941 | 5 | Societe Anglo-Franco-Belge | 2667 - 2671 | 120 - 124 |
| 1952 | 5 | Societe Anglo-Franco-Belge | 2682 - 2686 | 132 - 136 |
| 1957 |
5 | Henschel & Sohn | 29585 - 29589 | 144 - 148 |