4-10-2

4-10-2 (Reid Tenwheeler)

Front of locomotive at left

NGR Class C Reid Tenwheeler no. 171

Equivalent classifications UIC class 2'E1' French class 251 Turkish class 58 Swiss class 5/8 Russian class 2-5-1

First known tank engine version First use 1899 Country Colony of Natal Locomotive NGR Class C Railway Natal Government Railways Designer George William Reid Builder Dübs and Company Evolved from 4-8-2T

First known tender engine version First use 1925 Country United States of America Locomotive SP-2 class Railway Southern Pacific Railroad Designer American Locomotive Company Builder American Locomotive Company Evolved from 2-10-2

Under the Whyte notation for the classification of steam locomotives by wheel arrangement, 4-10-2 represents the arrangement of four leading wheels on two axles, usually in a leading bogie, ten powered and coupled driving wheels on five axles and two trailing wheels on one axle, usually in a trailing truck. 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.

This wheel arrangement was first used on the Natal Government Railways (NGR) in the Colony of Natal in 1899, on a 4-10-2 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.

In the United States, a simple expansion (simplex) version of the type was used only on the Southern Pacific and Union Pacific Railroads. Baldwin Locomotive Works built an experimental compound expansion 4-10-2 in 1926, but since the weight and length of this engine was too much for all but the heaviest and straightest track and compound steam locomotives had already lost favor on United States railroads, its demonstration runs failed to generate interest and no more were produced.

Brazil had 1,000 mm (3 ft 3 ³⁄₈ in) metre gauge 4-10-2 tender locomotives, built by Henschel in 1936. These were converted to 1,600 mm (5 ft 3 in) gauge in 1940.