4-4-2 (locomotive)

4-4-2 (Atlantic)
Diagram of two small leading wheels, two large driving wheels joined by a coupling rod, and one small trailing wheel
Front of locomotive at left
Milwaukee Road class A2 no. 919, built 1901
Equivalent classifications
UIC class2B1
French class221
Turkish class25
Swiss class2/5
Russian class2-2-1
First known tank engine version
First use1880
CountryUnited Kingdom
LocomotiveLT&SR 1 Class
RailwayLondon, Tilbury and Southend Railway
DesignerWilliam Adams
BuilderSharp, Stewart & Co. &
Nasmyth, Wilson & Co.
Evolved from4-4-0T
First known tender engine version
First use1888
CountryUnited States of America
LocomotiveExperimental double-firebox
DesignerGeorge Strong
BuilderHinkley Locomotive Works
Evolved from2-4-2
BenefitsMore 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]