A Pennsylvania Railroad class M1a at the 1939 World's Fair, June 16, 1939.
(By Original: Gottscho-Schleisner, Inc.derivative work:Morven at en.wikipedia - https://www.loc.gov/pictures/collection/gsc/item/gsc1994013438/PP/,
Public Domain, https://commons.wikimedia.org/w/index.php?curid=12523594)
4-8-2 MOUNTAIN, MOHAWK (NYC) STEAM LOCOMOTIVE
Under the Whyte notation for the classification of steam locomotives, 4-8-2 represents the wheel arrangement of four leading wheels, eight powered and coupled driving wheels and two trailing wheels. This type of steam locomotive is commonly known as the Mountain type, and referred to as a Mohawk on the New York Central Railroad.
Schematic of 4-8-2 steam locomotive wheel arrangement. Front is on the left.
(Gwernol, Public domain, via Wikimedia Commons)
United States
The 4-8-2 was most popular on the North American continent. When the 4-6-2 Pacific fleets were becoming over-burdened as passenger trains grew in length and weight, the first North American 4-8-2 locomotives were built by the American Locomotive Company (ALCO) for the Chesapeake & Ohio Railway (C&O) in 1911. It is possible that the "Mountain" name was originated by C&O, after the Allegheny Mountains where their first 4-8-2 locomotives were built to work. ALCO combined the traction of the eight-coupled 2-8-2 Mikado with the excellent tracking qualities of the Pacific's four-wheel leading truck. Although C&O intended their new Mountains for passenger service, the type also proved ideal for the new, faster freight services that railroads in the United States were introducing. Many 4-8-2 locomotives were therefore built for dual service.
A total of about 2,200 Mountain type locomotives were built for 41 American railroads. With 600 4-8-2 locomotives, the largest user in the United States was the New York Central Railroad (NYC), who named theirs the Mohawk type.
Other large users in the United States were the Pennsylvania Railroad with 224 Class M1, Class M1a and Class M1b locomotives that were used mostly for fast freight service, the Florida East Coast with ninety passenger locomotives, the New York, New Haven & Hartford Railroad with seventy, and the Southern Railway with fifty-eight. The heaviest 4-8-2s in the world were the twenty-three St. Louis–San Francisco Railway 4400 class locomotives, built by the railroad between 1939 and 1945, using boilers from older 2-10-2 locomotives, riding cast frames, and weighing over 449,000 pounds. These were a follow up to the road's 4300 class, similarly rebuilt at the road's Springfield, Missouri shops with some parts from 2-10-2s and new cast frames, but with new 250 psi boilers; these appear to be the most powerful Mountain types, tested by the railway's dynamometer at 4800 horsepower.
The Southern Pacific ordered a total of seventy-five MT-class 4-8-2s from ALCO for both freight and passenger service.
One notable example is SLSF 1522, one of thirty T-54 class Mountains built by Baldwin in 1926 and became one of two American 4-8-2 to have had an excursion career with the other being Illinois Central 2613. It ran excursions between 1988 until 2002, when rising insurance rates and a flue sheet cracked beyond repair forced it back into retirement. 1522 is now on display at the National Museum of Transportation in St Louis.
Lightweight 4-8-4 No. 7000 built by Alco for Union Pacific, ca. 1916.
(Internet Archive Book Images, No restrictions, via Wikimedia Commons)
Preservation - United States of America
Grand Trunk Western 6039: On display at Steamtown National Historic Site in Scranton, Pennsylvania.
Great Northern 2507: On display at the Wishram depot in Wishram, Washington.
Great Northern 2523: On display at the Kandiyohi County Historical Society in Willmar, Minnesota.
Illinois Central 2500: On display at the Age of Steam Memorial in Fairview Park in Centralia, Illinois.
Illinois Central 2542: On display at the McComb Railroad Museum in McComb, Mississippi.
New York Central 2933: On display at the National Museum of Transportation in Kirkwood, Missouri.
New York Central 3001: On display at the National New York Central Railroad Museum in Elkhart, Indiana. It is the largest surviving New York Central steam locomotive.
Pennsylvania Railroad 6755: On display at the Railroad Museum of Pennsylvania in Strasburg, Pennsylvania.
St. Louis–San Francisco 1501: On display at Schuman Park in Rolla, Missouri.
St. Louis–San Francisco 1519: On display at the Railroad Museum of Oklahoma in Enid, Oklahoma.
St. Louis–San Francisco 1522: On display at Museum of Transportation in Kirkwood, Missouri. Restored in 1988 and operated in excursion service until 2002.
St. Louis–San Francisco 1526: On display at the Museum of the Great Plains in Lawton, Oklahoma.
St. Louis–San Francisco 1527: On display at Langan Park in Mobile, Alabama.
St. Louis–San Francisco 1529: On display at Frisco Park in Amory, Mississippi.
Canada
The Angus Shops of Canadian Pacific (CP) built a pair of 4-8-2 locomotives in 1914. While they were not replicated, CP kept them in service for thirty years. CP reverted to 4-6-2 Pacific locomotives before moving on to the 4-6-4 Hudson.
Canadian National operated eighty U-1 class 4-8-2 locomotives in passenger service, built by Montreal Locomotive Works in 1944. The last twenty, designated the U-1-f class, were delivered with semi-streamlined conical smokebox covers that earned them the nickname of Bullet Nose Betty.