Day's predecessor as CME, A.G. Watson, as part of the latter's standardisation policy. To maintain approximately the same tractive effort as the Class 15E, the boiler pressure was raised to , at the time the highest yet used on the SAR since the SAR loading gauge did not permit horizontal cylinders of greater bore diameter than with normal cylinder spacing. The locomotives were delivered without smoke deflectors, but after the war they were fitted with standard elephant ear smoke deflectors based upon the Deutsche Reichsbahn design. The inner firebox was of steel and was fitted with five diameter arch tubes, which supported the brick arch. The rocking grate, with two drop-grates, was actuated by a steam shaker. As was the practice with Watson Standard boilers, the hopper type ashpan was secured to the main frames instead of to the boiler foundation ring, with a air gap all round. Drench pipes were fitted to facilitate cleaning and the bottom of the ashpan was fitted with a hand-operated sliding door. To enable them to negotiate radius curves, the leading coupled wheels were given a total side-play in their horn blocks, while the tyre flanges of the intermediate coupled wheels were of reduced thickness and the leading coupling rods were provided with spherical bearings at the knuckle joints and crank pins. In addition, largely also as a result of the decision to use the shorter Watson Standard boiler, it was decided to reduce the coupled wheel diameter from the originally intended to , which shortened the coupled wheelbase and would further ease passage on sharp curves. Tender Since these locomotives were intended for working in the Karoo where good quality water is a scarce resource, they were equipped with very large Type EW tenders which rode on six-wheeled bogies to enable longer runs to be undertaken between watering stops or to skip bad watering places. They were the largest tenders to have been used in South Africa up to that time and as originally designed, would have had a water capacity of and a coal capacity of . Owing to axle load restrictions, however, it was necessary to reduce the water capacity to . The first batch of twenty locomotives were delivered with such tenders. The second batch of 116 locomotives were delivered with a modification to the tender's underframe. To improve the weight distribution, both tender pivot centres were relocated towards the