history of the twelve wheeler can be traced as far back as the
Baltimore & Ohio Railroad prior to the Civil War. In 1855 the
B&O began construction of the Centipede, a 4-8-0 camelback
design. The locomotive did not actually begin service until late into
the war but it proved to be successful enough for the company that it
remained in use for nearly 20 years. The first true standard design of a
4-8-0 was not built until 1882 when the Central Pacific/Southern
Pacific began testing its Mastodon. This name stuck and became the
common term for the wheel arrangement aside from the twelve wheeler.
When tested the Mastodon was operated in the steep Sierra Nevada Mountains
of California on the CP/SP and the railroad quickly realized that the
4-8-0 could out pull its smaller rivals of the time, the American and
The SP went on to operate numerous 4-8-0s and the original 1882 units were listed as Class TW-4, numbered 51-75. They could produce 29,143 pounds of tractive effort and as with virtually all twelve wheelers was designed for use in freight service. Other SP classes for the locomotive ranged from TW-1 to TW-8 although the railroad owned others. Most were built by the American Locomotive Company's plant in Schenectady, New York although the railroad itself built others (a few were also built by the Cooke Locomotive Works, which merged to form Alco). In all the SP rostered well over 100 units, one of the most of any line. While the 4-8-0 was technically designed from the popular 2-8-0s of the time it was meant to be a more powerful freight unit that would replace the common wheel arrangements mentioned above to become the standard of the era.
One of the largest twelve wheelers ever built was for the Laurel &
Tullahoma Western, a logging line in the state of Mississippi. The
L&TW owned only one, #67, built by the Baldwin Locomotive Works
in 1911. The locomotive could produce more than 38,000 pounds of
tractive effort while its incredibly long wheelbase of nearly 58 feet
enabled it to operate on rail as light as 64 pounds (this was quite
important considering that most logging operations only used light
"stick" rail to reduce costs and keep production moving from one timber
site to the next). However, in terms of size and power for the mastodon
the Norfolk & Western was the clear leader in this regard.
Starting in 1906 the railroad began taking delivery of 4-8-0s from Alco
and Baldwin listed as Class M and numbered 375-499.
The N&W came to regard them as Mollies and were very pleased with their ability to pull and overall smooth riding quality. A year later the railroad began receiving Class M1s, numbered 1000-1099, which were neither as large nor as powerful as their earlier counterparts. It was the Class M2s of 1910 that gave the N&W the recognition of owning the largest and most powerful twelve wheelers. These locomotives, numbered 1100-1160, weighed between 428,600 and 447,030 pounds (with superheaters) and could produce over 50,000 pounds of tractive effort. Due to their extreme weight the 4-8-0s could only operate on rail between 90 and 100 pounds. Unfortunately, despite their power the railroad came to dislike their M2s; the steamers had a poor riding quality and had trouble holding steam due to a proportionately small firebox.
While the M2s were problematic most of the N&W's 4-8-0s went on to operate for many years and were slowly retired
in the 1930s and 1940s as newer power completely replaced them on the
roster (remember that the N&W did not abandon main line steam
operations until the late 1950s). Other railroads to operate twelve
wheelers included the Buffalo Rochester & Pittsburgh, Chicago &
Eastern Illinois, Fitchburg, Jersey Central, Santa Fe Pacific, Fremont
Elkhorn & Missouri Valley, Great Northern, Lackawanna, Central
Railroad of Pennsylvania (CNJ), Duluth & Iron Range, Lehigh Valley,
Illinois Central, Monon, Northern Pacific, Missouri Pacific, Nashville
Chattanooga & St. Louis, Nacional de Mexico, Beech Creek Clearfield
& Western, Union Pacific, and the Winston-Salem Southbound. Today,
one 4-8-0 is still operational, N&W Class M #475 on the Strasburg Railroad.
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