From TrainSpottingWorld, for Rail fans everywhere

In Whyte notation, a 0-6-4 is a railroad steam locomotive that has six coupled driving wheels followed by four trailing wheels, with no leading wheels .

The equivalent UIC classification is C2'.

Largely in the United States the 0-6-4 locomotive was built only for usage in railyards as essentially an 0-6-0 switch engine with an extended firebox or a reconstruction of a 4-6-0 with a larger firebox, and thereby a neccesity for the movement of the leading wheels.