N&W 475 at Leaman Place Junction, August 16, 2020.

(Trainsfan1331, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons)



Under the Whyte notation for the classification of steam locomotives, 4-8-0 represents the wheel arrangement of four leading wheels on two axles, usually in a leading truck, eight powered and coupled driving wheels on four axles and no trailing wheels. In North America and in some other countries the type was usually known as the Twelve-wheeler.


Diagram of the 4-8-0 Wheel Arrangement. Front of locomotive on left.

(Gwernol, Public domain, via Wikimedia Commons)



The first 4-8-0 locomotive is believed to have been the Centipede, a tender locomotive built by Ross Winans in 1855 for the Baltimore and Ohio Railroad in the United States of America, where it remained in service for nearly twenty years. It appears to have been delivered in a cab-forward type of configuration that was modified to a Camel configuration in 1864. On a Camel locomotive the cab was mounted atop the boiler, unlike the later Camelback locomotive whose cab straddled the boiler and that first appeared around 1877.


Centipede as built in 1855 shown below. Above is after 1864 modifications by the B&O Railroad.

(C. B. Chaney, Public domain, via Wikimedia Commons)


CPR No. 229, the Mastodon of 1882

The nickname Mastodon is often mistakenly used to describe the 4-8-0 wheel arrangement and was derived from the unofficial name of the first 4-8-0 locomotive of the Central Pacific Railroad in the United States, the wood-fired CPR no. 229, which was designed and built in 1882 by the railroad's master mechanic, Andrew Jackson (A.J.) Stevens, at the railroad's Sacramento works in California. However, several period publications instead use the nickname Mastodon to refer to the 4-10-0. These publications refer to the 4-8-0 as the Twelve-wheeler.


A painting by Richard Ward of Central Pacific No. 229 "Mastodon," in Rocklin, California, 1885. Painted in 1963.

(Guy L. Dunscomb (24 May 1915-1 Sept 2000), Public domain, via Wikimedia Commons)


United States

In the United States, the 4-8-0 was essentially a freight locomotive that was a development of the 2-8-0 Consolidation. Most American 4-8-0 locomotives were built in the late 19th or early 20th century. The type never achieved great popularity, although there were five occasions when a 4-8-0 locomotive was considered as the heaviest and/or most powerful in the world upon its introduction. Those locomotives were the No. 20 Champion of the Lehigh Valley Railroad in 1880, the No. 229 Mastodon (see above image) of the Central Pacific Railroad in 1882, the G5 class of the Great Northern Railway in 1897 and the No. 640 of the Illinois Central Railroad in 1899. It is noteworthy that the Great Northern G5 had 16-inch-diameter (410 mm) piston valves, as large as the pistons of many locomotives then in service.

Finally, the Duluth and Iron Range Railway ordered a number of trim-lined Mastodons, beginning in 1893, which were reportedly the heaviest freight engines constructed at the time. They had long, between-the-drivers fireboxes and a relatively short stroke for freight engines of the era. They were numbered from 60 to 89 and became the railroad's class J. After 1900, they were gradually phased out in favor of the more conventional Consolidation type. All were scrapped by 1933.

N&W class M
Even though, at the time, the wide-firebox 2-8-2 Mikado had much more potential as far as speed is concerned, the Norfolk and Western Railway opted for the class M 4-8-0 (see image top of page) for its shorter wheelbase that enabled it to have over 90 percent of the locomotive's weight on the driving wheels, and the four-wheel leading truck for greater stability. The N&W operated 4-8-0s from the early 1900s to the late 1950s. Built by Baldwin Locomotive Works from 1906 and nicknamed Mollies, the class M, class M1 and class M2 became the most numerous American class of 4-8-0.

Norfolk & Western class M2
The class M2 locomotives (see photo below) are often mistakenly believed to be the largest conventional 4-8-0s built, but the Mexican PR-8 was over four tons heavier. Many of them lasted into the 1950s, but were poor steamers since the boiler's heating surface had been significantly increased compared to the classes M and M1, but with no corresponding improvement of firebox volume and grate area.

A total of six 4-8-0s are left to survive in the United States, Southern Pacific 2914, Norfolk and Western 433, 475, 1118, 1134, and 1151, and one of them, No. 475, continues to operate for the Strasburg Rail Road in Strasburg, Pennsylvania.


A Class M2 4-8-0 locomotive built by the Baldwin Locomotive Works for the Norfolk and Western Railway.

(1922 Locomotive Cyclopedia of American Practice, Public Domain, via Wikimedia Commons)



4-8-0 locomotives in Mexico were almost entirely built in the United States. The first locomotives were provided by the Southern Pacific Railroad to independent and subsidiary railroads such as the Cananae, Rio Yaqui & Pacifico and Sud Pacifico de Mexico. The Sud Pacifico de Mexico used, in total, 14 of the Southern Pacific's 4-8-0s, including a few from CRY&P, all constructed at Schenectady between 1889 and 1895.

The National Railways of Mexico had four classes of 4-8-0. The first two orders were relatively small locomotives from Brooks in 1897. In 1924, a much larger locomotive was ordered, the PR-7, numbers 5-A to 2856 and weighing 127 tons. Unusually among American-built 4-8-0s, these were intended for express passenger service and therefore had much larger drivers than 4-8-0s operating in the United States, at 67 inches diameter. The cylinders had an unusually square bore and stroke of 28 x 28 inches. Because the firebox was wide and above the frames, the tops of the last set of drivers projected into the firebox, something which was only possible due to them being oil fired.

In 1935, a further five locomotives were built with larger boilers, which increased the evaporative heating surface by 357 square feet and the superheater surface by 172 square feet. These were designated PR-8, numbers 3000 to 3004. At 144 tons, the PR-8 was the heaviest conventional 4-8-0 ever built. The Norfolk & Western's M2, which is often credited as being the heaviest conventional 4-8-0, weighed 8,470 pounds (3,842 kg) less than the PR-8.


Ferrocarriles Nacionales de México (NdeM) class PR-8 4-8-0 No. 3002. These were the largest and heaviest 4-8-0's built.

(Unknown photographer, W. Lenheim Collection)



Equivalent classifications

UIC class: 2′D
French class: 240
Turkish class: 46
Swiss class: 4/6
Russian class: 2-4-0
First known tank engine version
First use: 1909
Country: United Kingdom
Locomotive: NER Class X
Railway: North Eastern Railway
Designer: Wilson Worsdell
Builder: North Eastern Railway
First known tender engine version
First use: 1855
Country: United States of America
Locomotive: B&O No. 235 Centipede
Railway: Baltimore and Ohio Railroad
Designer: Ross Winans
Builder: Ross Winans
First known "True type" version
First use: 1882
Country: United States
Locomotive: 229 Mastodon
Railway: Central Pacific Railroad
Designer: Andrew Jackson Stevens
Builder: Central Pacific Sacramento shops
Evolved from: 2-8-0
Evolved to: 4-8-2
Benefits: Better power than 2-8-0
Drawbacks: Small firebox.