Mallet steam locomotives are known for being the most popular style of compound articulated steam locomotives in the USA during the steam era even though they were introduced in the USA over two decades after being invented. Let’s dive into the history of this fascinating locomotive type with a tricky name!
Mallet locomotives appeared in the United States in the early 1900s when compound locomotives were becoming more and more popular. The Mallet locomotive referred to an articulated compound steam locomotive designed with two sets of cylinders compounded together. This meant that a Mallet steam locomotive essentially had two engines on one frame and coupled with six or more sets of axles. This made it more powerful in terms of horsepower and tractive effort; features that made these locomotives quite popular, especially with railroads that operated in mountainous regions.
Let’s Start With the Pronunciation!
Before getting into details and history, we should start with the pronunciation. Although one may think it is said the same way as synonym for a hammer, the locomotive is sneaky thanks to its Central European roots. The correct pronunciation is ‘Mal-lay’.
A Brief History of the Mallet Steam Locomotive
The beginning of this powerful locomotive can be traced back to the 1870s when Swiss engineer Anatole Mallet patented a cross-compounding steam locomotive that he named after himself. After gaining the patent to the system in 1874, he built the first locomotive based on this principle in 1876. His first Mallet locomotive had a wheel arrangement of 0-4-2T and was built for the Bayonne & Biarritz Railway before other railroads in Europe followed suit.
It wasn’t until more than two decades later that the concept of the Mallet steam locomotive reached the North American shores in the early 1900s at a time when compound steam locomotives were all the rage. The first Mallet locomotive in the United States was built by ALCO in 1904 for the Baltimore & Ohio Railroad. It had a wheel arrangement of 0-6-6-0 and was nicknamed the “Old Maude” perhaps because of its speed limitations.
The new locomotive style would quickly gain popularity throughout the country and the Baldwin Locomotive Works improved on the first one by building more powerful and quicker versions.
Norfolk & Western was the last known major railroad company in the United States to use Mallets, which they removed from service in July 1959.
Are Big Boys Locomotives Mallets?
While many assume that Union Pacific Big Boy locomotives are mallets, they technically are not. In order to be a true Mallet, a locomotive must be articulated and utilize compound expansion, where the first steam was designed to use two high-pressure cylinders, which would then be used in the two larger low-pressure cylinders at the front of the locomotive.
Big Boys on the other hand used simple expansion where involved the use of four cylinders and steam would be fed directly to all four cylinders. Nonetheless, there was no specific name for this design, so they were loosely referred to as Mallets.
Surviving Mallet Locomotives
Although it has been more than 60 years since Mallets were in active service, many have been preserved and are either on static display or even operate on heritage railroads throughout the country. Our Steam Survivor series features several Mallet locomotives, including: Black Hills Central #108 and #110, Western Maryland Scenic #1309, and Niles Canyon’s Skookum.