By the 1940's, the Chesapeake & Ohio Railway (C&O) and Lima Locomotive Works developed a new type of steam locomotive that could tackle the tough Allegheny Mountain grades more efficiently than the current 2-6-6-2's and 2-8-8-2's. The new locomotive had a 109-inch wide boiler, which was 2 inches larger than the "Big Boy" locomotive and a fire box that was so large it required a six-wheel trailing truck to support it. The locomotive only had six axles, instead of the usual eight. This new 2-6-6-6 locomotive was known as the "Allegheny" after the mountains it was designed to conquer.
