Pennsylvania Railroad I1s

The Pennsylvania Railroad class I1s was a heavy freight steam locomotive of the 2-10-0 Decapod wheel arrangement, and the most numerous class of its type in the United States. Between 1916 and 1923 the railroad and the Baldwin Locomotive Works built 598 of them, 123 at the railroad's own Altoona Works. Crews nicknamed them Decs and Hippos for their large boiler. They had small drivers that favoured pulling power over speed, so they were limited to 35 miles per hour in service and rode roughly above that. Most were later converted to the I1sa subclass, which admitted steam for a longer part of the piston stroke and raised starting tractive effort. They were the main drag freight engine on the system until World War II and served until 1957.