Some early electric locomotives also used Krauss-Helmholtz bogies. The Class NG15 had larger tenders than the Class NG5 with a working order weight of , compared to the of the Class NG5's tender. The tenders had low-slung sides, with the bottom part of the water tank extending down to below axle level on either side of the tender bogies to lower the vehicle's roll centre on the narrow track gauge. The original tenders were built as flat-sided box-shaped vehicles. A second tender version was delivered with the later batches of locomotives, with the coal bunker sides set inward for reasons unknown. The new shape made no difference to the crew's rearward field of vision and the only likely benefit was a reduced axle load as a result of the reduced coal capacity. In SWA, the Class Hd, Class NG5 and Class NG15 Mikado locomotives operated in a common pool. They were the most powerful non-articulated narrow-gauge steam locomotives in SAR service. In 1960, when all the SWA narrow-gauge lines were widened to Cape gauge, the Class Hd and Class NG5 locomotives were withdrawn from service while the 21 Class NG15 locomotives were all shipped to Port Elizabeth for use on the Langkloof line to Avontuur. The first one was offloaded in Port Elizabeth in April 1961, still equipped with a single central buffer and side chains, the preferred drawgear on the ex-German lines in SWA. Their arrival increased the number of locomotives on the Avontuur Railway from a total of 23 in March 1961 to 43 by July. As a result, all but one of the Class NG10 as well as Class NG G11 no. 51, South Africa’s first Garratt, were withdrawn from service by July 1962. On the Avontuur Railway, the Class NG15 was nicknamed "Kalahari", inappropriately so since its previous stamping ground was across the Namib desert to the west of the Kalahari. Garratts initially continued to operate in the Langkloof since the Class NG15 was not allowed to work beyond Humansdorp from Port Elizabeth because of a lack of turning facilities, the only existing triangle at the time being the one at the end of the line at Avontuur. More turning facilities had not been required until then since the Langkloof had for years been the domain of bi-directional Garratt locomotives.