Between 1898 and 1905, more than fifty pairs of Zwillinge twin 0-6-0T steam locomotives were delivered to the Swakopmund-Windhuk Staatsbahn (Swakopmund-Windhoek State Railway) in German South West Africa.

The 382-kilometre long (237-mile) Swakopmund-Windhuk Staatsbahn, later named the Northern State Railway or Nordbahn, was officially opened to traffic nearly five years later, on 1 July 1902.

[2][3] The railway was initially intended for temporary military purposes only, to be worked by means of animal power such as Argentine mules or Cape donkeys, but steam traction was soon adopted.

The track was laid on steel sleepers with 19 pounds per yard (9 kilograms per metre) rail and had very severe curves and gradients.

This created an alternative line from Windhoek to the Atlantic Ocean at times when the section through the Khan River gorge suffered from the occasional flooding.

[1][2] They were built by six manufacturers, Krauss and Company, Henschel and Son, L. Schwartzkopff, Egestorf, Machinenbau Anstalt and Arnold Jung.

[5] As indicated by their name Zwillinge (twins), they were actually two separate locomotives which were designed to be semi-permanently coupled back-to-back at the cabs, allowing a single footplate crew to fire and control both engines.

[2][6][7] The principle of using two tank locomotives which are semi-perma­nently coupled at their cab ends was patented in 1855 by the English loco­motive builders Robert Stephenson and Company.

[5][7] Shortly after the first Zwillinge locomotives were placed in service, it was found that the tank engine's fuel and water capacities were insufficient for the distances which had to be covered in the German colonies in Africa, especially in the harsh conditions presented by the Namib Desert which had to be crossed between Swakopmund and Windhoek.

154A was employed in Windhoek as a non-revenue departmental locomotive and was finally withdrawn from service in 1939, after logging a total mileage of about 371,000 miles (597,000 kilometres).

169B, built in 1904 by Maschinenbau-Anstalt Humboldt, was shipped to Cape Town after the First World War and placed in non-revenue service at the Bellville quarry into the side of the Tygerberg.

Apart from the twelve Brigadeloks, the first of another type of small twin locomotives known as Pugs by the enginemen and probably employed on shunting duties, were delivered in 1901 from Machinenbau Anstalt of Breslau, with boilers supplied by Krauss and Company.

The boiler pitch was 3 feet 7+5⁄16 inches (1,100 millimetres) and the engine weight in working order was 7 long tons 0 hundredweight 3 quarters (7,150 kilograms).