The Rhodesian Railways had been using the 16th class since 1929, which was a Garratt with 2-8-2+2-8-2 wheel arrangement and showed good running characteristics. However, there was a desire for a locomotive with larger wheels that could also be used to pull faster trains on flatter routes. The 4-6-2+2-6-4 wheel arrangement was initially considered. However, the 15th class developed as a result was ultimately based on the class 250 of the Sudan Railways, which had the 4-6-4+4-6-4 wheel arrangement, which is also known as “Double Baltic” or “Double Hudson”.
The first production lot was just four engines, delivered by Beyer, Peacock & Co. in 1940. They were intended for the almost 800 km long line between Bulawayo and Mafeking in South Africa, which led through Bechuanaland (now Botswana). However, the bridges on this route could not be upgraded due to the war. Instead they were used on the Salisbury-Gwelo route, replacing the 12th class 4-8-2 locos.
Another 30 engines were made between 1947 and 1949. From 1949 another 30 engines of a modified variant followed, which had an increased boiler pressure of 200 instead of 180 psi and were designated class 15A. In 1952 there were ten more of this design, the production of which had been handed over to Franco-Belge and which, thanks to thermic syphons, had a larger firebox heating surface. The total number of 74 made them the second most built Garratt locomotive.
They were later used on the originally planned line through Botswana and were the only locomotives there until the DE2 class diesel locomotives arrived on this line in 1973. They could haul passenger trains weighing 550 tons at more than 50 mph and were also used in front of freight trains weighing 1,000 tons. The boilers of the engines of 15th, 15A and 16th classes were often exchanged.
After the founding of Zambia on the territory of the former Northern Rhodesia, some examples went to the Zambia Railways. In Southern Rhodesia, the state of Zimbabwe was only formed in 1980, so the remaining engines went to the National Railways of Zimbabwe. Since the planned retirement had to be postponed for financial reasons, the class 15A locomotives were modernized between 1980 and 1983. They were named after African animals.
After the non-modernized 15th class locomotives were soon phased out, the class 15A was renamed the 15th class. The modernized locomotives were not retired until after the turn of the millennium and ten were even reactivated in 2006 and 2007 and underwent some necessary repairs. Two of these were leased to the Hwange Mining Company until 2018, making them the last steam locomotives in Africa to be in regular service.