4-8-4

Under the Whyte notation for the classification of steam locomotives, **4-8-4** represents the wheel arrangement of four leading wheels on two axles, eight powered and coupled driving wheels on four axles and four trailing wheels on two axles. The type was first used by the Northern Pacific Railway, and initially named the Northern Pacific, but railfans and railroad employees have shortened the name since its introduction. It is most-commonly known as a **Northern**.

## Overview

The 4-8-4 wheel arrangement was a progression from the 4-8-2 Mountain type and, like the 2-8-4 Berkshire and 4-6-4 Hudson types, an example of the "Super Power" concept in steam locomotive design that made use of the larger firebox that could be supported by a four-wheel trailing truck, which allowed greater production of steam. The four-wheel leading truck gave stability at speed and the eight driving wheels gave greater adhesion. The evolution to the 4-8-4 type occurred in the United States of America soon after the Lima Locomotive Works introduced the concept of "Lima Super Power" in 1925, making heavy 2-8-2 and 2-8-4 locomotives. The prototype was built by American Locomotive Company (ALCO) for the Northern Pacific Railway (NP) in 1926, with a very large firebox with a 100-square-foot (9.3 m2) grate, designed to burn low quality lignite coal. The four-wheel trailing truck weighed about 15,000 pounds (6.8 t) more than two-wheel trucks of the time and could carry an additional 55,000 pounds (25 t) of engine weight; the difference of 40,000 pounds (18 t) was available for increased boiler capacity.

The 4-8-4 type arrived when nearly all the important steam locomotive design improvements had already been proven, including Superheaters, mechanical stokers, outside valve gear and the Delta trailing truck. One-piece, cast steel bed-frames with integrally cast cylinders gave the strength and rigidity to use Roller bearings. In 1930, the Timken Company used the Timken 1111, a 4-8-4 built by ALCO with roller bearings on all axles, to demonstrate the value of their sealed roller bearings. The Timken 1111 was subsequently sold to the NP, where it became NP No. 2626, their sole Class A-1 locomotive.

The stability of the 4-8-4 wheel arrangement meant that driving wheels up to 80 inches (2.0 m) diameter could be used for high speed passenger and fast freight operation. Lateral control devices allowed these locomotives to traverse relatively sharp curves despite their eight-coupled drivers. The increased boiler size possible with this type, together with the high axle loads permitted on mainlines in North America, resulted in the design of some massive locomotives, some of which weighed as much as 450 tons, including the tender. The 4-8-4 was suitable for both express passenger and fast freight service, though it was not suited to heavy drag freight trains.

Although locomotives of the 4-8-4 wheel arrangement were used in a number of countries, those that were developed outside North America included various design features which set them apart from North American practice. Scaled down examples of the type were exported by two American builders, ALCO and Baldwin Locomotive Works, for 1,000 mm (3 ft 3+3⁄8 in) metre gauge lines in Brazil. Most were two-cylinder locomotives, but five classes of three-cylinder 4-8-4s were built:

* The simplex 06 class by the Deutsche Reichsbahn in Germany.
* The simplex H class by the Victorian Railways in Australia.
* The compound 242A1 class of the Société nationale des chemins de fer français (SNCF) in France.
* The simplex 477 class tank engines by CKD for Czechoslovak State Railways; 60 4-8-4T locomotives were built between 1951 and 1955, the last new steam engines built in Czechoslovakia.
* An experimental high-pressure compound locomotive of the New York Central (NYC).

### The Northern name

Since the 4-8-4 was first used by the Northern Pacific Railway, the type was named "Northern". Most North American railroads used this name, but some adopted different names.

* "Heavy Mountain" or "New Mountain" on the Atchison, Topeka, and Santa Fe (ATSF). Original blueprints of class 3751 designate the 4-8-4 as a "Mountain" or "Heavy Mountain". The index to the blueprints reference the 3751 class as "Mountain, 4-Wheel Trailer". Early correspondence of the ATSF refer to this type as "New Mountains". The Santa Fe never adopted the "Northern" designation.
* "Big Apple" on the Central of Georgia Railway (CG).
* "Confederation" on the Canadian National Railway (CN), named because they were purchased in 1927, the 60th anniversary of Canada's confederation in 1867. The "Confederation" 4-8-4s were later renamed by the CN to the generic "Northern" name in later years.
* "Dixie" on the Nashville, Chattanooga and St. Louis Railway (NC&StL).
* "Golden State" on the Southern Pacific Railroad (SP), temporarily renamed "General Service" during the Second World War and also referred to as "GS" by Western Pacific for those GSs which were diverted to the WP from SP's order by the War Production Board.
* "Greenbrier" on the Chesapeake and Ohio Railway (C&O).
* "J" on the Norfolk and Western Railway (N&W).
* "FEF" (Four-Eight-Four) on the Union Pacific Railroad (UP).
* "Niagara" on the New York Central Railroad (NYC).
* "Niágara" on the Ferrocarriles Nacionales de México (N de M) and in Brazil.
* "Pocono" on the Delaware, Lackawanna and Western Railroad (Lackawanna).
* "Potomac" on the Western Maryland Railway (WM).
* "Western" on the Denver and Rio Grande Western Railroad (Rio Grande).
* "Wyoming" on the Lehigh Valley Railroad (LV).

The Richmond, Fredericksburg and Potomac Railroad (RFP) gave each of its three 4-8-4 classes a separate name, the "General" of 1937, the "Governor" of 1938 and the "Statesman" of 1944.

### Demise

The big-wheeled 4-8-4 was at home on heavy passenger trains and quite capable of speeds over 100 miles per hour (160 kilometres per hour), but freight was the primary revenue source of the railroads; in that service the Northern had limitations. The adhesive weight on a 4-8-4 was limited to about 60% of the engine's weight, not including the dead weight of the tender. Henry Bowen, the Chief Mechanical Engineer of the Canadian Pacific Railway (CPR) from 1928 to 1949, tested the first two CPR K-1a Northerns introduced by his predecessor, then he designed a 2-10-4 Selkirk type using the same boiler. The resulting T-1a Selkirk locomotive had the same number of axles as the Northern, but the driving wheels were reduced from 75 to 63 inches (1.9–1.6 m) in diameter, while the additional pair of driving wheels increased the tractive effort by 27%. In a later variant, Bowen added a booster to the trailing truck, enabling the Selkirk to exert nearly 50% more tractive effort than the similar-sized K-1a Northern.

When it was demonstrated that a three-unit EMD F3 diesel-electric consist that weighed slightly less than the total engine and tender mass of a CPR K-1a Northern could produce nearly three times its tractive effort, high-powered steam locomotives were retired as quickly as finance allowed.