In 1929, when Mr Allan G. Watson became the Chief Mechanical Engineer of the SAR, one of his earliest tasks was to provide additional motive power for express passenger traffic on the section Beaufort West - Kimberley - Johannesburg.
He decided to take an existing design as the basis for a new locomotive. The Pacific (4-6-2) type with its very large driver wheels was, at that stage, still regarded as a suitable type for fast passenger working over the easier graded sections. Thus the existing class 16DA served as the basis for the design of the new locomotives.
The major modification to the original design was changing to a wide firebox (just over 5½ square meters). To accomplish this, the main frame was shortened to end at the front of the firebox. This allowed a much larger ashpan and firegrate area. Apart from the wide fireboxes, the new locomotives were so similar to the original 16DA's that they were also classified 16DA, and numbered 874 - 879. Fitting wide fire-boxes to these engines was obviously a seen as a beneficial venture by Mr Watson as literally 100's of later main line locomotives of various classes had wide fire-boxes incorporated in their designs.
Had normal SAR conventions been followed, the Henschel build version of the 16DA should have been known as the 16DB. Later, when 879 was re-boilered, the naming convention would have required an addition of an 'R', so by rights 879 would have been classed as a 16DBR. This however did not happen, so the 16DA class has a wide variety of variations.
At that time, the price paid per locomotive was £7,445 0.0d. Of the six wide-box 16DA locomotives, five were provided with Walschaerts valve motion, but the sixth engine  was fitted with Caprotti valve gear, and ran with this until 1940, when she was converted at the Bloemfontein mechanical workshops to Walschaerts motion.
The 'wide-box' 16DA's all entered traffic with five foot coupled wheels and a boiler pressure of 195psi. Four of the six engines [No's 874,875,878 and 879] subsequently had their coupled wheels increased in size to five feet three inches. The boiler pressures of these locomotives were also increased to 205psi which resulted in a tractive effort to 33,570 lb at 75% boiler pressure.
Initially, these locomotives were stationed in Kimberley and worked fast passenger trains like 'The Union Limited' between Beaufort West, Kimberley and Johannesburg. Together with the earlier 16DA's and the later 16E's, the wide firebox 16DA's remained on the work already detailed until the arrival of air-conditioned stock for the 'Union Limited' in 1939. Together with their sister Pacifics, these engines were transferred to Bloemfontein to work passenger traffic in the Orange Free State, and up until 1953 they worked passenger trains through to Johannesburg. The 'wide-box' DA's also worked the Orange Express for quite a few years, particularly between Bloemfontein and Kimberly.
However, the 'Pacific' type locomotive lost favour on the SAR, as it could not be regarded as a general mixed traffic type with the accent on goods working. Being more of a passenger locomotive, the Class 16DA 'wide-box' was ultimately relegated to lesser and lesser duties such as 'pick-up' goods work until final retirement of the class in 1973.
Three of the wide-box 16DA have been preserved. 876 "Lettie Uys" and 879 "Theodora" (as she was called then) were restored as a 'Live Steam' exhibits of the Transnet Museum, while 878 is plinthed at the Transnet Rail Engineering workshops in Bloemfontein. 876 and 879 were operated as part of the Transnet Heritage Collection where 879 was given a blue "Union Limited" livery. As luck would have it, 879 was sent to Dal Josafat Depot and had undergone a full boiler refurbishment when the THF steam safaris were ended. 879 was towed to the Epping Market and left in the care of the Cape Western Railway Preservation Society.
After a few years at the Epping Market, Atlantic Rail took over the task to preserve/restore the locomotive. Since 879's boiler had been overhauled completely just before she was mothballed, re-certification of the boiler was a viable option. As luck would have it, at this point in time a major factory in the Cape was in desperate need of a steam boiler as theirs had to be shut down for maintenance. Previously, Atlantic Rail had been able to use SAR Class 24 #3655 to help out in such cases but she was scheduled for quite a few passenger trips and was not available. The factory agreed to help pay towards getting the 879 roadworthy while she was fired to produce steam for the factory. Initial work was completed at the factory site, but she was dangerously exposed to metal thieves at that site. Although the thieves did not get away with much metal. Their cutting and smashing caused considerable damage and it was with the help of crowd-sourcing donations that Atlantic Rail could afford to hire a security company and repair the damage done.
On the 3rd May 2013, Atlantic Rail finally managed to bring 879 to their home base station where she is now kept safe together with 3655. She has had extensive further repairs and tunings.
6 April 2014 saw her do her first test run on the open line, hauling a complete eight car 10M3 Metrorail set as a load. At the controls was Mr Frikkie Gerber and he was assisted by fireman Brett Radloff. The test was passed with flying colours. The same team took her on her first trip to Simon's Town on 27 April 2014. A ceremony was held where she was renamed "Katie" in honour of Atlantic Rail Director Ian Pretorius' grand-daughter and daughter of Atlantic Rail Director Sarah-Jane Nielsen.
879 is important as a preserved locomotive, as it is the only current running passenger main line steam locomotive in South Africa.
The focus can now shift to more cosmetic repair and maintenance and since the loan agreement with Transnet Freight Rail (the owners) has been signed she can now become one of the staple of regular engines that lead Atlantic Rail trips.