In 1931 the first three locomotives of what became Class N15 were designed by the SAR and built by Henschel and Son of Kassel for the 352 mile long 600mm gauge Otavi Mining and Railway Company in South West Africa, linking Swakopmund on the Atlantic coast with Tsumeb and Grootfontein across the Namib desert.
The new Mikados were based both on SAR's existing NG5 and the Otavi company's Hd Classes. The drawing board work for the future Class NG15 has been attributed to the one time Chief Mechanical Engineer of the Otavi Railway, a German known in South West Africa as Mr. Peters, who was also employed as a draughtsman South African Railways. The usual practice of the SAR at the time was to design locomotives in their own drawing offices and to then go out and find a builder. In South West Africa the Otavi Class Hd, Class NG5 and Class NG15 Mikado locomotives all operated in a common pool.
The three Otavi Class Hd 2-8-2 locomotives, built by Henschel with builder's works numbers 10720 to 10722, were supplied on lease to the Otavi Mining and Railway Company in Deutsche-Sudwest-Afrika (DSWA) by the German government in 1912 and numbered 40 to 42 in the Otavi fleet. These locomotives had piston valves and, at 59.9 tonnes were considerably larger than earlier main line Otavi locomotives, which typically weighed less than 23.4 tonnes in full working order.
The Otavi Class Hd locomotives came into SAR ownership in 1923 when the Otavi Railway was nationalised and ex Otavi Railway locomotives had the prefix SW (for South West) added to their existing numbers to distinguish them from SAR narrow gauge locomotives that bore the same number.
Among these SW40 is believed to have been the last locomotive in steam on the narrow gauge Otavi Railway during September 1961, shortly before the demolition of the line was completed. It was then placed on display at Usakos station, which had become the southern terminus and works location of the narrow gauge line after World War I.
Meanwhile, SW41 was retained with the intention to display it in a museum in the Namibian capital Windhoek. In 1960 it was plinthed at Otijiwarongo station, where it remained in August 2007. Number SW42 was sold as scrap in 1962.
Six similar Henschel built locomotives were placed in service in 1922, subsequently classified as Class NG5 by the SAR who had become responsible for operating all railways in South West Africa after World War I. These locomotives had slide valves instead of the piston valves that were used on the Class Hd and the driving wheel suspension arrangement also differed.
One of these Class NG5 locomotives was regauged and sent to the two foot (610 mm) gauge Port Elizabeth to Avontuur line. Lightly laid through magnificent scenery of the Langkloof Valley, this 150 mile line into a fruit growing area of the Drakensburg escarpment was only busy during the harvest season of Cape apples and despite the NG5 having one set of flangeless driving wheels the tight curves proved too much for it and the 2-8-2 returned to South West Africa. All six Class NG5 locomotives were sold for scrap in 1962.
The original 1931 Mikados were numbered 17 to 19 while the three locomotives of the next batch - built in 1939 - were numbered 117 to 119. Eventually five batches of similar 2-8-2s were purchased for the Otavi and for the Tsumeb Copper Corporation, bringing the total number up to twenty-one by the end of production in 1958.
Ten more of these locomotives were built for the Otavi line by Societe Franco-Belge and delivered in two batches of five in 1950 and 1953, numbered 120 to 124 and 132 to 136 respectively. In 1958 the last five locomotives, once again built by Henschel, were delivered to the Tsumeb Copper Corporation, numbered TC1 to TC5, for use by the SAR in terms of an agreement between the SAR and the Corporation.
Since the earlier trials with the Class NG5 locomotive, the sharpest curves on the Avontuur line had been eased and the experience gained in the process was taken into consideration during the design of the future-designated Class NG15. The leading pair of driving wheels had a limited amount of sideplay and were linked to the leading pony truck while the axle of the leading driving wheels still remain parallel to the other three driving axles at all times.
This linking of a pony truck and driving axle is known as a Krauss-Helmholtz bogie, an invention of Richard von Helmholtz who was the chief designer at the Krauss works in Munich from 1884 to 1917. On 4' 8 1/2" gauge railways in Europe the inclusion of a Krauss-Helmholtz bogie has allowed the use of large 2-10-0 locomotives on sharply curved mountain sections. Some early electric locomotives also used Krauss-Helmholtz bogies.
However in 1960 the Otavi Railway was, like many similar narrow gauge lines in southern Africa, regauged to the Cape standard of 3'6".
As a result the NG5 and Hd 2-8-2s were retired and the Krauss-Helmholtz bogie Mikados were taken over by South African Railways ( later Spoornet and Transnet Freight Rail ) and re-gauged and transferred to the Eastern Cape for further service on the Port Elizabeth to Avontuur line. Here they were officially designated Class NG15 but known as Kalaharis despite working across the Namib desert and being anything but pygmy!
Indeed, during the last years of steam traction on the Avontuur line the Class NG15 was unique in being the only non-Garratt steam locomotive working in the Langkloof Valley. Outside the apple season the Class NG15 became well known for hauling the Apple Express from the Humewood Road railway station to Loerie and back every Saturday to cater for tourists. It gained further fame when the Apple Express instituted an annual train race marathon where athletes could compete against an Apple Express filled with spectators.
During the 1970s steam traction in the Langkloof began to be replaced by diesel power with the introduction of General Electric built Class 91-000 diesel-electric locomotives in 1973. Diesel and steam served the Langkloof together for some years, but by the mid 1980s road transport had triumphed over rail transport on the apple route as well, and the narrow gauge steam fleet was retired.
However, a number of Class 15s have been preserved, including number 120 on the Welsh Highland Railway and number 17 on Sandstone Estates in South Africa.
