The American Locomotive Company 4000-class 4-8-8-4 locomotive, popularly named Big Boy, is an articulated, coal or oil-fired, steam locomotive manufactured between 1941 and 1944 and operated by the Union Pacific Railroad in revenue service until 1959. The Big Boy fleet of twenty five locomotives was initially built to haul freight over the Wasatch mountains between Ogden, Utah and Green River, Wyoming. In the late 1940’s, they were reassigned to Cheyenne, Wyoming, where they hauled freight over Sherman Hill to Laramie, Wyoming. They were the only locomotives to use a 4-8-8-4 wheel arrangement consisting of a four-wheel leading truck for stability entering curves, two sets of eight driving wheels and a four-wheel trailing truck to support the large firebox. According to a Union Pacific executive, this 4000-class 4-8-8-4 series originally was to have been called the “Wasatch”. One day while one of the engines was being built, an unknown worker scrawled “Big Boy” in chalk on its front. With that, the legendary name was born and has stuck ever since. Only two preserved Big Boys remain in operable or close-to-operable condition: the 4012 and the 4014.
Our club, the Mendocino Coast Model Railroad & Historical Society, owns one. We run it VERY rarely as it just does not fit in a logging operation railroad such as ours. The pic below is the only one I have of it running on the layout. The run was in the early days of the layout and we used it to test to see if the curves on the main line were large enough to accommodate very large locos. I am pleased to say that the test was a success and the main line can handle any G scale loco.