2-10-0

2-10-0 (Decapod)

Front of locomotive at left

Pennsylvania Railroad class PRR I1s, the most successful class of such locomotives in North America. Note the firebox placed above the rear drivers.

Equivalent classifications UIC class 1′E French class 150 Turkish class 56 Swiss class 5/6 Russian class 1-5-0

First known tender engine version First use 1886 Country United States Locomotive No. 1 & 2 Railway Northern Pacific Railroad Designer Burnham, Parry, Williams & Company Builder Burnham, Parry, Williams & Company Evolved from 0-10-0 Evolved to 2-10-2 Benefits Better stability than the 0-10-0 Drawbacks Small firebox

Under the Whyte notation for the classification of steam locomotives, 2-10-0 represents the wheel arrangement of two leading wheels on one axle, ten powered and coupled driving wheels on five axles, and no trailing wheels. This arrangement was often named Decapod, especially in the United States, although this name was sometimes applied to locomotives of 0-10-0 "Ten-Coupled" arrangement, particularly in the United Kingdom. Notable German locomotives of this type include the war locomotives of Class 52.

These locomotives were popular in Europe, particularly in Germany and Russia; British use of the type was confined to the period during and after World War II. In the United States, the 2-10-0 was not widely popular but was a favorite of a small number of railroads which operated mostly in mountainous terrain. Among these was the Erie Railroad, a major Chicago to New York trunk line railroad, and the Pennsylvania Railroad, whose heavily graded routes crossed the Allegheny Mountains.

The 2-10-0's main advantage was that five out of six of its axles were powered, meaning almost all the weight was available for traction rather than being distributed over pilot and trailing wheels. The long rigid wheelbase caused problems on tightly curved track, so blind drivers were the norm, either on the central axle, and/or on the second and/or fourth axles. Often lateral motion devices were attached to the leading drive axle.

The wheel arrangement's disadvantages included the firebox size restriction caused by the lack of trailing wheel. This meant the firebox was fitted in between the wheels (common on earlier locomotives) and was long and narrow, or if mounted above the driving wheels, was wide and long but shallow. Many locomotives chose the latter option. A firebox mounted over the drivers also restricted the diameter of the driving wheels, which in turn limited speed. As with the Consolidation (2-8-0), "chopping" at speed ensured a rough ride for the crew due to instability caused by the wheel arrangement. In fact, backing any locomotive without a trailing axle was restricted to under twenty miles per hour or less. Most 2-10-0s were not operated at speeds greater than 50 mph (80 km/h).

The type operated as freight engine, although locomotives in Germany and the United Kingdom proved capable of hauling passenger trains.