The Chicago and North Western Railway was well-known for its extensive passenger service across the Midwest, with its famous 400" series of trains becoming a symbol of travel between Chicago and the Upper Midwest. When the time came to modernize these iconic trains, the railroad sought a streamlined locomotive to match their sleek design. The result was the Class ES Pacific steam locomotive.
Built in 1930 by Alco, the ES locomotives were originally intended for the "400s." However, before the engines were even delivered, C&NW management decided to shift focus away from streamlined steam power and instead placed orders for new diesel locomotives from General Motors' Electro-Motive Division. As a result, the ES locomotives were reassigned to other passenger services until they were retired and scrapped in 1953. Crews affectionately nicknamed them "Yellow Jackets" because of their distinctive yellow and green paint schemes.
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