The class 59 of the East African Railways wasn't only the most powerful and heaviest Garratt locomotive ever built for meter gauge, but most likely also heavier than all built for cape gauge and nearly as heavy as the heaviest standard gauge Garratts in Australia and the Soviet Union. They were designed to accelerate freight traffic on the 330 miles between Mombasa and Nairobi. While Mombasa is located on the coast, Nairobi's elevation is 1.661 m or 5.450 ft above sea level.

Their wheel arrangement 4-8-2+2-8-4 is also called “Double Mountain”, since it resembles two 4-8-2 “Mountain” locomotives coupled back to back. In fact, the 34 locomotives built by Beyer-Peacock in 1955 were named after mountains. Their task was to haul 1,200 ton trains up long inclines of 1.5 percent. When needed, they also had to take over express trains with 35 coaches.

For the whole of their lives, they operated on the same line. Many of their crews only consisted of Sikhs. These always kept their locomotive in the best and cleanest condition and decorated their cab in a special way. After all had been withdrawn between 1973 and 1980, No. 5918 “Mount Gelai” was overhauled at the Nairobi Railway Museum. Until 2005, it wasn't only used to haul excursion trains, but sometimes even had to stand in when there was a shortage of diesel locomotives.