Under the Whyte notation for the classification of steam locomotives, a 2-10-10-10-10-10-2 has two leading wheels, five sets of ten driving wheels, and two trailing wheels. Because of its length, such a locomotive must be an articulated locomotive. It is not longer than a normal articulated; the fourth and fifth sets of drivers are located under the tender.
Other equivalent classifications are:
UIC classification: 1-E-E-E-E-E-1 (also known as German classification and Italian classification)
AAR classification: 1-E-E-E-E-E-1
French classification: 150+050+050+050+051
Turkish classification: 56+55+55+55+56
Swiss classification: 5/6+5/5+5/5+5/5+5/6
The equivalent UIC classification is to be refined to (1'E)EEE(E1').
The Baldwin Locomotive Company submitted a design for a 2-10-10-10-10-10-2 quintuplex to the Atchison, Topeka, and Santa Fe Railway. The proposed quintuplex was essentially a cross between the cab-forward locomotives for the Southern Pacific and the Triplexes built for the Erie and Virginian, with a cab at the front for the driver and the rear cab for the fireman. The locomotive was a compound, with cylinders operating at only two pressures; the HP cylinders 7 on the drawing above were fed from the forward boiler and worked at high pressure, a horizontal pipe taking the exhaust from 7 to 8 which worked at low pressure. HP cylinders 9 were fed from the rear boiler and exhausted through another horizontal pipe to LP cylinders 10. (The designer very sensibly avoided the temptation to go for quadruple-expansion, as used in some marine steam engines) The draught was provided not by an exhaust steam blast, but by a steam-turbine driven fan driven 26 exhausting through the funnel 19. The exhaust steam from the LP cylinders went straight to atmosphere via the funnels 33 and 38. The last two sets of driving wheels were under the tender. Not surprisingly, the failure of the Triplex concept meant that the 2-10-10-10-10-10-2 never made it off the drawing board.