4-4-2 Atlantic Steam Locomotive
Under the Whyte notation for the classification of steam locomotives by wheel arrangement, 4-4-2 represents a configuration of four leading wheels on two axles, usually in a leading truck with a single pivot point, four powered and coupled driving wheels on two axles, and two trailing wheels on one axle, usually in a trailing truck which supports part of the weight of the boiler and firebox and gives the class its main improvement over the 4-4-0 configuration.

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 working.

While the wheel arrangement and type name Atlantic would come to fame in the fast passenger service competition between railroads in the United States by mid-1895, the tank locomotive version of the 4-4-2 Atlantic type first made its appearance in the United Kingdom in 1880, when William Adams designed the 1 Class 4-4-2T of the London, Tilbury and Southend Railway (LT&SR).

The 4-4-2T is the tank locomotive equivalent of a 4-4-0 American type tender locomotive, but with the frame extended to allow for a fuel bunker behind the cab. This necessitated the addition of a trailing truck to support the additional weight at the rear end of the locomotive. As such, the tank version of the 4-4-2 wheel arrangement appeared earlier than the tender version.

The tender version of the 4-4-2 originated in the United States of America, evolving from the less stable 2-4-2 Columbia type wheel arrangement, and was built especially for mainline passenger express services. One advantage of the type over its predecessor 4-4-0 American type was that the trailing wheels allowed a larger and deeper firebox to be placed behind the driving wheels.

The first use of the 4-4-2 wheel arrangement for a tender locomotive was under an experimental double-firebox locomotive, built to the design of George Strong at the Hinkley Locomotive Works in 1888. The locomotive was not successful and was scrapped soon afterwards. The wheel arrangement was named after the second North American 4-4-2 tender locomotive class, built by the Baldwin Locomotive Works in 1894 for use on the Atlantic City line of the Philadelphia and Reading Railway.

Baldwin's ideas on 4-4-2 tender locomotives were soon copied in the United Kingdom, initially by Henry Ivatt of the Great Northern Railway (GNR) with his GNR Class C1 Klondyke Atlantic of 1898. These were quickly followed by John Aspinall's Class 7, known as the High-Flyer, for the Lancashire and Yorkshire Railway (L&YR).

United States of America
The original Atlantics in the United States were built with the hauling of wood-frame passenger cars in mind and came in a variety of configurations, including the four-cylinder Vauclain compound which had previously been used on express 4-4-0 American, 4-6-0 Ten-wheeler and 2-4-2 Columbia locomotives. Around the 1910s, railroads started buying heavier steel passenger cars, which precipitated the introduction of the 4-6-2 Pacific type as the standard passenger locomotive. Nonetheless, the Chicago and North Western, Southern Pacific, Santa Fe and Pennsylvania railroads used 4-4-2 Atlantics until the bitter end of steam locomotive fleets in the 1950s, with some even being used in light local freight switching service.

Pennsylvania Railroad E6s Class
One of the best-known groups of 4-4-2s in the United States was the Pennsylvania Railroad's vast fleet of E class Atlantics, culminating in the PRR E6s class.

Although Atlantics were sometimes used as mountain helpers prior to the First World War, they were not well-suited for mountain or for very long distance operations. They had large-diameter driving wheels, in some cases exceeding 72 inches (1,829 millimeters), which were adequate for 70 to 100 miles per hour (110 to 160 kilometers per hour) trains, although they tended to oscillate at higher speeds. Climbing any substantial grade required a smaller driving wheel diameter for better adhesion, or more driving wheels for better traction.

The Hiawatha
The Chicago, Milwaukee, St. Paul and Pacific Railroad (Milwaukee Road) used a streamlined Atlantic type on its Midwestern Hiawatha passenger train service that was instituted in 1935. Four 4-4-2 locomotives of the Milwaukee Road class A were constructed for this service in 1935. These 4-4-2s were reportedly the first steam locomotives ever designed and built to reach 100 miles per hour (160 kilometers per hour) on a daily basis.

These Atlantics with their distinctive streamlining shrouds were designed by industrial designer Otto Kuhler. Their calculated tractive effort was 30,685 pounds-force (136 kilonewtons). An unusual feature of this locomotive was the drive onto the front coupled axle, which improved riding quality at speed.

The locomotives were cross balanced and ran on 84 inches (2,134 millimeters) drivers. They had an oil-fired 69 square feet (6.4 square meters) grate and a rated boiler pressure of 300 pounds per square inch (2,100 kilopascals), which gave the boiler a high capacity in relation to the cylinders. Designed for a light-weight train of five to six passenger cars, they were considered as probably the fastest steam locomotives ever built in the United States, possibly capable of matching any locomotive in the world. The fleet covered their 431 miles (694 kilometers) schedule in 400 minutes with several stops en route, at an average speed of more than 100 miles per hour (160 kilometers per hour) on some sections and often arriving with one or two minutes to spare.

None survived, since all four locomotives were withdrawn and scrapped between 1949 and 1951.

Preserved locomotives
Several 4-4-2 locomotives were preserved in the United States. Bearing in mind that this information may become outdated over time, some known examples are:

Southern Pacific no. 3025 at the Travel Town Museum in Los Angeles, CA.
Chicago & North Western no. 1015 at the Museum of Transportation in St. Louis, MO.
Pennsylvania Railroad E6s no. 460 at the Railroad Museum of Pennsylvania in Strasburg, PA.
Pennsylvania Railroad no. 7002, formerly no. 8063, at the Railroad Museum of Pennsylvania in Strasburg, PA. It has steamed since preservation, but is now static.
Detroit, Toledo & Ironton no. 45 at the Henry Ford Museum in Dearborn, MI.
Central Railroad of New Jersey no. 592 at the B&O Railroad Museum in Baltimore, MD.

4-4-2 Atlantic Overview
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: Tank version of 4-4-0
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

See also:

Milwaukee Road Class A

Steam Locomotives

An example of the4-4-2 Whyte notation (left to right): leading truck with a single pivot point, four powered and coupled driving wheels on two axles, and two trailing wheels on one axle.
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The 4-4-2 Whyte notation (left to right): leading truck with a single pivot point, four powered and coupled driving wheels on two axles, and two trailing wheels on one axle.

Milwaukee Road 4-4-2 Atlantic No. 919.

Milwaukee Road 4-4-2 Atlantic No. 919.