The first locomotives of the 2-6-6-2 wheel arrangement were built in 1906 by the Great Northern Railway to permit longer trains on their heavily graded line over the Cascade Mountains.

In North America the 2-6-6-2 wheel arrangement was most often used for articulated compound steam Mallet locomotives.

In a compound Mallet, the rear set of coupled wheels are driven by the smaller high pressure cylinders, from which spent steam is then fed to the larger low pressure cylinders that drive the front set of coupled wheels.

Chesapeake and Ohio 1309 is now operating on Western Maryland Scenic Railroad after a restoration completed in December 2020.

North American builders also produced such engines for service on logging railroads, and for export to Santo Domingo, Serbia, India, and South Africa.

Additional examples were built by North British Locomotive Works for South Africa, and a single experimental engine by the Soviet Union.

[10] "Super Power" steam locomotives with feedwater heaters and four wheel trailing trucks were introduced in 1925, allowing greater firebox area and higher horsepower.

In 1931 their leading and trailing trucks were removed, resulting in an 0-6-6-0 wheel arrangement, and they were used in yard service.

[25] The most unusual engines of this wheel arrangement were the twelve cab-forward examples built for the Southern Pacific Railroad, class MM-2, in 1912.

One derailed while pulling the Overland Limited at Applegate, California in 1912,[26][27][28] and they were soon converted to 4-6-6-2 by replacing the front truck with a four-wheel design,[29] and re-designated class AM-2.

[32] They had a rigid two-section boiler with a feedwater heater occupying the front half, and were designed to burn low quality lignite coal.

Commonly each railroad would buy a small lot; satisfied customers would order more, typically with improvements to meet their specific requirements.

Alco built these locomotives at its Schenectady and Brooks plants in New York state, and at Richmond, Virginia.

[34] They were primarily used to haul freight trains out of the Connecticut River Valley in both directions from Springfield, Massachusetts.

After completion of the Alfred H. Smith Memorial Bridge in 1924, traffic from New England no longer descended into the valley and fewer such engines were needed at Albany.

[35] All of the 1300 series engines of both roads had a total weight in working order of 363,800 pounds (approximately 165 tonnes) and a coupled length of 85 feet, 7+1⁄4 inches (26.09 meters).

[38] The Chesapeake and Ohio Railway ordered its first 2-6-6-2 engine in 1910, from the Schenectady plant of Alco, and a second was purchased used from the Chicago and Alton Railroad.

[39] In 1912 the Norfolk and Western Railway purchased 15 copies of the Chesapeake and Ohio engine from the Richmond plant of Alco, which they designated as Class Z.

[40] The Chicago and Alton Railroad purchased three 2-6-6-2 engines from the Brooks plant of Alco, also in 1910, one of which was almost immediately sold to the Chesapeake and Ohio Railway.

[41] Denver and Rio Grande purchased eight 2-6-6-2 engines, Class 340/L-62, built by the Schenectady plant of Alco, in 1910.

[52] Between 1919 and 1924 the Chesapeake & Ohio, the New York Central, and the Western Pacific purchased additional locomotives of their preferred designs.

The Verde Tunnel & Smelter Company purchased two coal fueled engines from the Schenectady works in 1920 and operated them between Jerome and Clarksdale, Arizona.

During World War II they were sold to the Southern Pacific Railroad, converted to burn oil, and placed in class MM-3.

They were used in helper and branch line service on the Los Angeles Division until 1951 and 1954 [53]Southern Pacific Engine No.

ALCo locomotives exported to Mexico, Serbia and South Africa are discussed under the headings for those countries below.

[63][64] The South African Railways (SAR) operated 22 Mallet locomotives with this wheel arrangement, spread over five classes, all of them built to 3 ft 6 in (1,067 mm) Cape gauge.

The Serbian government used 10 Mallet articulated compound locomotives for freight service on 2 ft 6 in (762 mm) narrow gauge.

This led to smaller production lots over which to allocate the research and design costs and consequently, significantly higher list prices.

[72] An O scale model of a Great Northern 2-6-6-2 was built by Kumata & Co. as their item E-330-A and imported by Custom Brass in 1979.

As discussed above, the USRA engines were initially allocated to C&O and W&LE, later Nickel Plate; Norfolk & Western did not receive any.