Milwaukee Road class A2 No. 919, built by Baldwin 1901. Click to enlarge.

(This media file is in the public domain in the United States, via Wikimedia Commons)



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.

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.


Diagram of the 4-4-2 wheel arrangement. Front of locomotive at left. Click to enlarge.

(By Gwernol - Own work, Public Domain,



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 Coast Line of the Philadelphia and Reading Railway.

Baldwin's ideas on 4-4-2 tender locomotives were soon utilized 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).


A 4-4-2 inspection locomotive of the Philadelphia and Reading Railroad. Click to enlarge.

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


United States

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 end of steam locomotive use in the 1950s, with some even being utilized in local freight and switching service.


Pennsylvania Railroad class E6s 4-4-2 steam locomotive No. 1067. Click to enlarge.

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


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 grades. They had large-diameter driving wheels, in some cases exceeding 72 inches (1,829 mm), which were adequate for 70 to 100 miles per hour (110 to 160 km per hour) trains. They tended to oscillate at higher speeds when the drive rods were connected to the rear pair of drivers. This was not standard practice in the U.S., however. The nation's biggest user of the type was the Santa Fe with 178 of the type. All of these were built with 73 inches (185 cm) or 79 inches (201 cm) drivers and the drive rods connected to the first pair of driving wheels.

In 1905, Santa Fe engineer Charles Losee was widely reported to have driven Atlantic type 510, a 1904 balanced compound built by Baldwin, the 2.8 miles (4.5 km) from Cameron to Surrey in Illinois with a three car special train in one minute and thirty-five seconds. If that had been confirmed by a disinterested party, the 106 miles (171 km) per hour speed would have set a world record. These were never used on the road's Rocky Mountain grades; even on the flat plains of Kansas the Atlantics were soon overwhelmed by the weight of the newest all-steel, 85 feet (26 m) passenger cars. Despite their excellent performance, most were retired long before other locomotives of their era, and the few survivors wound up on light local trains.


Milwaukee Road class A No. 1 in 1951. Click to enlarge.

(Audio-Visual designs, Earlton, NY, photo: Russ Porter, Public domain, via Wikimedia Commons)


Milwaukee Road

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 km 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 kN). 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 mm) drivers. They had an oil-fired 69 square feet (6.4 square m) grate and a rated boiler pressure of 300 pounds per square inch (2,100 kp), 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 km) schedule in 400 minutes with several stops en route, at an average speed of more than 100 miles per hour (160 km 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 National 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.
Michigan Central No. 254 (later No. 7953, then New York Central No. 8085 before being sold to the Detroit, Toledo & Ironton Railroad as 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


See also:

Steam Locomotives