4-4-4-4

First known tender engine version
First known tender engine version
First use	May 1937
Country	United States
Locomotive	B&O Class N-1
Railway	Baltimore and Ohio Railroad
Designer	Baltimore and Ohio Railroad
Builder	Mount Clare Shops
Benefits	Decreased wheelbase
Drawbacks	Premature cylinder wear, cylinder clogging and restricted firebox size

Equivalent classifications
Equivalent classifications
UIC class	2'BB2'
French class	2222
Turkish class	2424
Swiss class	4/8
Russian class	2-2-2-2

4-4-4-4
	Front of locomotive at left
	The Baltimore and Ohio Railroad's #5600 George H. Emerson.
UIC class
Equivalent classifications
UIC class	2'BB2'
French class	2222
Turkish class	2424
Swiss class	4/8
Russian class	2-2-2-2
First use
First known tender engine version
First use	May 1937
Country	United States
Locomotive	B&O Class N-1
Railway	Baltimore and Ohio Railroad
Designer	Baltimore and Ohio Railroad
Builder	Mount Clare Shops
Benefits	Decreased wheelbase
Drawbacks	Premature cylinder wear, cylinder clogging and restricted firebox size
First use
First known "True type" version
First use	April 1942
Country	United States
Locomotive	PRR class T1
Railway	Pennsylvania Railroad
Designer	Ralph P. Johnson; Raymond Loewy
Builder	Baldwin Locomotive Works; Altoona Works
Evolved from	4-8-4
Benefits	Better high speed performance
Drawbacks	Wheel slip

A 4-4-4-4 steam locomotive, in the Whyte notation for describing locomotive wheel arrangements, has a four-wheel leading truck, two sets of four driving wheels, and a four-wheel trailing truck. While it would be possible to make an articulated locomotive of this arrangement, the only 4-4-4-4s ever built were duplex locomotives—with two sets of cylinders driving two sets of driven wheels in one rigid frame, essentially a 4-8-4 with divided drive.