The 4-6-4+4-6-4 was the fifth most common Garratt wheel arrangement, with 84 locomotives constructed, 74 by Garratt patent owner Beyer, Peacock & Company between 1936 and 1950 and ten under sub-contract from Beyer, Peacock by Belgian manufacturer Société Franco-Belge in 1952.[1][2]
In 1964, ten ex-Sudanese 250 class locomotives were purchased by the Caminhos de Ferro de Moçambique from the Rhodesia Railways, who had acquired them from Sudan c. 1949 and used them as their 17th class. In Mozambique, they were used on the Beira railway from the port city of Beira to the Rhodesian (now Zimbabwean) border at Umtali (now Mutare). They remained in use into the 1980s, but their ultimate post-civil war fate is unclear and all of them are presumed to have been scrapped.[3]
The 15th class was a development of the RR 16th class 2-8-2+2-8-2 Garratts, to meet a requirement for a locomotive with a larger driving wheel diameter for higher speed train service on the more level parts of the railway. After examining the Sudan Railways 250 class, the RR settled on a design with the same wheel arrangement and the same 57 inches (1,448 millimetres) diameter driving wheel diameter as that of the Sudanese Double Baltics.[3]
Initially four locomotives were ordered in 1940, and having proved their worth, a further seventy locomotives were ordered in five batches after the Second World War. The last forty locomotives were designated as the 15A class, since they had boilers with the rated pressure increased from 180 to 200 pounds per square inch (1.24 to 1.38 megapascals).[3]
Sudan
Ten 4-6-4+4-6-4 Garratt locomotives of the Sudan Railways 250 class were built in two batches for the Sudan Railways by Beyer, Peacock in 1936 and 1937. They were the only Garratt types on the Sudan Railways and were used on the Port Sudan to Atbara and Atbara to Wad Madani routes, until they were made redundant by diesel locomotives in 1949.[3]
They were then sold to the Rhodesia Railways, where they were designated 17th class and used alongside the RR’s 15th and 15A classes. In 1964, all ten locomotives were sold to the Caminhos de Ferro de Moçambique.[3]