   big boy is the popular name of the american locomotive company 4000-class 4-8-8-4 articulated, coal-fired, steam locomotives manufactured between 1941 and 1944 and operated by the union pacific railroad until 1959. the big boy fleet totaled twenty five locomotives that were used primarily in the wyoming division to haul freight over the wasatch range between [[green
4-8-8-4_locomotives ALCO_locomotives Freight_locomotives Railway_locomotives_introduced_in_1941 Simple_articulated_locomotives Standard_gauge_railway_locomotives Steam_locomotives_of_the_United_States Union_Pacific_Railroad_locomotives