still being ordered prior to 1929. The Class 19C was the first to be built new with Watson Standard boilers. The no. 1A boiler had a larger superheater than the Class 19B. In a break with prior custom, the ash pan and running boards were affixed to the locomotive frame instead of to the boiler to facilitate easier removal of the boiler for repairs. The Class 19C was also built with Watson's altered cab with a slanted front to facilitate access to the firebox stays on the sides ahead of the cab. The Watson cab, like the Watson Standard boiler, was to become standard on later SAR steam locomotive classes. The first five Watson Standard boilers to be designed were the numbers 1, 1A, 2, 2A and 2B. The no. 1 boiler was suitable for the Classes 5, 5B, 10A, 10B and 10C locomotives. The no. 1A boiler was similar to the no. 1, but with the boiler barrel lengthened by , and was suitable for the Classes 19, 19A and 19B. Like the Class 19C, the Class 19D would also be built new with no. 1A boilers. The no. 2 boiler was suitable for the Classes 3, 3B, 4A, 12, 12B, 14, 14A and 14C locomotives. The no. 2A boiler was similar to the no. 2, but with the boiler barrel lengthened by , and was suitable for the Classes 15, 15A and 15B locomotives. The no. 2B boiler was also similar to the no. 2, but with the boiler barrel shortened by , and was suitable for the Classes 16, 16B and 16C locomotives. These were later followed by the numbers 3A and 3B boilers. The no. 3A boiler was suitable for the Class 16E locomotive, while the no. 3B boiler was longer and suitable for the Classes 15E, 15F, 21 and 23 locomotives. Copper and steel fireboxes Some of the locomotives were built with steel fireboxes for use in those areas where good or treated water was readily available, while others were still equipped with copper or composite fireboxes for use in areas with poor water quality. Copper or composite fireboxes are considerably more expensive to manufacture and repair than steel ones. It was only by the late 1960s, when severe corrosion was no longer a big problem as a result of the availability of water treatment facilities throughout the country, that copper and composite fireboxes were