The Mallet-Consolidation or MC-class engines were built with 57" drive wheels, with the Mallet Compound design using the high pressure steam from the boiler first in the fixed cylinder set under the middle of the boiler, then reusing the steam in the low pressure cylinders, which were much larger, on the radial engine, beyond the smokebox. These new engines could haul more tonnage than a standard Consolidation, more efficiently and with only one crew.