Under the Whyte notation, a 2-8-4 is a steam locomotive that has two unpowered leading wheels, followed by eight coupled and powered driving wheels, and four trailing wheels. This locomotive type is most often referred to as a Berkshire, though the Chesapeake and Ohio Railway used the name Kanawha for their 2-8-4s. In Europe, this wheel arrangement was mostly seen in mainline passenger express locomotives and, in certain countries, in tank locomotives.
Nickel Plate Road 765, a typical American 2-8-4, on an excursion train ca. 2018
WAGR K class 2-8-4T with pipe train, ca. 1902
BBÖ Class 114 No. 12.10 at the Eisenbahnmuseum Strasshof, 2007
Deutsche Bundesbahn Class 65
The Whyte notation is a classification method for steam locomotives, and some internal combustion locomotives and electric locomotives, by wheel arrangement. It was devised by Frederick Methvan Whyte, and came into use in the early twentieth century following a December 1900 editorial in American Engineer and Railroad Journal.
Whyte notation from a handbook for railroad industry workers published in 1906