Under the Whyte notation for the classification of steam locomotives by wheel arrangement, represents the arrangement of four leading wheels, ten powered and coupled driving wheels and two trailing wheels. In South Africa, where the wheel arrangement was first used, the type was known as a Reid Tenwheeler. In the United States of America it was known as a Southern Pacific on the Southern Pacific Railroad and as an Overland on the Union Pacific Railroad.
Overview
This wheel arrangement was first used on the Natal Government Railways (NGR) in the Colony of Natal in 1899, on a tank locomotive that was designed to meet the requirement for a locomotive that could haul at least one and a half times as much as an NGR Dübs A 4-8-2T locomotive.
Usage
Brazil
thumb|Brazilian 4-10-2 at the Museum of Technology, São Paulo
Brazil had 5 1600mm gauge 4-10-2 tender locomotives, built by Henschel in 1938.
South Africa
Between 1899 and 1903, the Natal Government Railways (NGR) placed 101 tank locomotives in service. The locomotive was designed by G.W. Reid, the Locomotive Superintendent of the NGR at the end of the nineteenth century, and built in Scotland by Dübs and Company and the newly established North British Locomotive Company. On the NGR, the locomotive type became known as the Reid Tenwheeler and was officially designated Class C.
The locomotive used saturated steam and was equipped with Allan straight link valve gear. The trailing wheels were of the Cartazzi type that allowed the axle some lateral movement. In order to negotiate sharp curves, both the first and fifth sets of coupled wheels were flangeless, but since the blind trailing coupled wheels had a tendency to derail while reversing, particularly over points, their tyre width was later increased from to . In 1912, after the establishment of the South African Railways, the surviving unmodified NGR locomotives were designated Class H.
thumb|[[CSAR Class E 4-10-2T|CSAR Class E]]
In 1901 and 1902, towards the end of the Second Boer War, the Imperial Military Railways also acquired 35 Reid Tenwheeler locomotives from Dübs and Company and Neilson, Reid and Company. After the war, they came onto the roster of the Central South African Railways (CSAR), who designated them Class E. In 1903, the CSAR modified six of them to South African Class H1 4-8-2T| locomotives and, beginning in 1905, the remainder to South African Class 13 4-8-0T+T| tank-and-tender locomotives.
A final order for one new Reid Tenwheeler was placed by Witbank Collieries as late as 1927. The total of 137 locomotives built to this design was about double the number of all other locomotives in use elsewhere in the world, all of which were tender locomotives that served in the United States and Brazil.
In 1925, the SP placed an order for sixteen locomotives with the American Locomotive Company (ALCO) and, later in the same year, the UP ordered one. The first SP locomotive, no. 5000, was completed in April 1925, while the UP locomotive, no. 8000, was completed the following month. Within a few months, the SP ordered more of these engines and built up a fleet of 49. The UP, on the other hand, waited thirteen months before repeating orders and establishing a fleet of ten locomotives. All 59 were simplex locomotives and were built by ALCO.