4-4-2 (locomotive)

4-4-2 (Atlantic)

Front of locomotive at left

Milwaukee Road class A2 no. 919, built 1901

Equivalent classifications UIC class 2B1 French class 221 Turkish class 25 Swiss class 2/5 Russian class 2-2-1

First known tank engine version First use 1880 Country United Kingdom Locomotive LT&SR 1 Class Railway London, Tilbury and Southend Railway Designer William Adams Builder Sharp, Stewart & Co. & Nasmyth, Wilson & Co. Evolved from 4-4-0T

First known tender engine version First use 1888 Country United States of America Locomotive Experimental double-firebox Designer George Strong Builder Hinkley Locomotive Works Evolved from 2-4-2 Benefits More stable than 2-4-2, Wide & deep firebox

Under the Whyte notation for the classification of steam locomotives by wheel arrangement, 4-4-2 represents a configuration of a four-wheeled leading bogie, four powered and coupled driving wheels, and two trailing wheels supporting part of the weight of the boiler and firebox. This allows a larger firebox and boiler than the 4-4-0 configuration.^{[citation needed]}

This wheel arrangement is commonly known as the Atlantic type, although it is also sometimes called a Milwaukee or 4-4-2 Milwaukee, after the Milwaukee Road, which employed it in high speed passenger service.^{[citation needed]}