The five engines of the Chesapeake & Ohio's J-3a class, erected by Lima Locomotive Works in 1948, were the final members of the railroad's third group of 4-8-4s. They were among the most modern conventional steam locomotives, being equipped with advanced features including an exhaust steam injector (in place of a feedwater heater), a multiple front end throttle, and roller bearings not only on all axles but also on all rods and other driving components. Sustaining 255 p.s.i. of boiler pressure, they had 27½x30-inch cylinders and 74-inch drivers. Their grate area totaled 100 square feet, their evaporative heating surface 4821 square feet, and their superheating surface 2058 square feet. Although the heating surface was nominally less than that of the earlier J-3 classes, the J-3a class had firebox circulators, a larger combustion chamber, and larger-diameter flues to accommodate the superheater tubes, improving their steaming capacity. These locomotives weighed 482,200 pounds and produced 66,453 pounds of tractive effort. The C&O — a railroad whose heritage lay below the Mason-Dixon line — called its 4-8-4s the "Greenbrier" type rather then the usual name "Northern." This Lima builder's photo in three-quarter view has become iconic for modern steam design.