0-4-2ST

0-4-2 (Olomana)

Front of locomotive at left

The Stephenson 0-4-2, 1834

Equivalent classifications UIC class B1 French class 021 Turkish class 23 Swiss class 2/3 Russian class 0-2-1

First known tank engine version First use c. 1860s Country United Kingdom

First known tender engine version First use 1834 Country United Kingdom Railway Stanhope and Tyne Railway Designer Robert Stephenson Builder Robert Stephenson and Company Benefits Better adhesion than the 2-2-2

Under the Whyte notation for the classification of steam locomotives, 0-4-2 represents the wheel arrangement with no leading wheels, four powered and coupled driving wheels on two axles and two trailing wheels on one axle. While the first locomotives of this wheel arrangement were tender engines, the configuration was later often used for tank engines, which is noted by adding letter suffixes to the configuration, such as 0-4-2T for a conventional side-tank locomotive, 0-4-2ST for a saddle-tank locomotive, 0-4-2WT for a well-tank locomotive and 0-4-2RT for a rack-equipped tank locomotive. The arrangement is sometimes known as Olomana after a Hawaiian 0-4-2 locomotive of 1883.

The earliest recorded 0-4-2 locomotives were three goods engines built by Robert Stephenson and Company for the Stanhope and Tyne Railway in 1834.

The first locomotive built in Germany in 1838, the Saxonia, was also an 0-4-2. In the same year Todd, Kitson & Laird built two examples for the Liverpool and Manchester Railway, one of which, LMR 57 Lion, has been preserved. The Lion had a top speed of 45 miles per hour (72 kilometres per hour) and could pull up to 200 tons (203 tonnes).

Over the next quarter of a century, the type was adopted by many early British railways for freight haulage since it afforded greater adhesion than the contemporary 2-2-2 passenger configuration, although in time they were also used for mixed traffic duties.