These ten locomotives were built by the American Locomotive Company (ALCO) at their Schenectady, New York plant between April and November 1918 for the Virginian Railway Company to haul long heavy freight trains. With a width of 144 inches (3,658 mm), they were delivered without their cabs and front low-pressure cylinders; and were assembled after delivery. The 48-inch (1,219 mm) low-pressure cylinders (on 90-inch or 2,286-millimetre centers) were the largest on any U.S. locomotive; the cylinders had to be inclined a few degrees to provide clearance. The boiler was also the largest diameter of any locomotive; Railway Mech Engineer says "the outside diameter of the largest course is 112 7⁄8 inches (2,867 mm)." but the drawing shows 118 1⁄2 inches (3,010 mm) diameter at the rear tube sheet. Their accompanying fuel tenders were shorter than usual so the locomotive would fit on the Virginian's turntables.
This class were compound Mallet locomotives. The rear, high-pressure cylinders exhausted their steam into the huge front cylinders. They could also be operated in simple mode for starting; reduced-pressure steam could be sent straight from the boiler to the front cylinders at low speed, for maximum tractive effort.
The calculated tractive effort was 147,200 lbf (66,800 kg) in compound; or 176,600 lbf (80,100 kg) in simple for the Virginian locomotives. These locomotives were capable of tackling 17,000 ton coal trains without a helper locomotive.
The class remained in service until they were retired between 1948 - 1958 (with engines #805 being the final engine to retire in May 1958). No locomotive example of this type survived into preservation.