2-10-2

Under the Whyte notation for the classification of steam locomotives, ' represents the wheel arrangement of two leading wheels, ten powered and coupled driving wheels, and two trailing wheels. In the United States and elsewhere the is known as the Santa Fe' type, after the Atchison, Topeka and Santa Fe Railway that first used the type in 1903.

==Overview== The wheel arrangement evolved in the United States from the 2-10-0 Decapod of the Atchison, Topeka and Santa Fe Railway (ATSF). Their existing 2-10-0 tandem compound locomotives, used as pushers up Raton Pass, encountered problems reversing back down the grade for their next assignments since they were unable to track around curves at speed in reverse and had to run very slowly to avoid derailing. Consequently, the ATSF added a trailing truck to the locomotives which allowed them to operate successfully in both directions. These first locomotives became the forerunners to the entire family.