The last steam locomotives built for service in North America by a commercial builder were the ten Mallet compound 2-6-6-2s the Chesapeake & Ohio ordered from Baldwin Locomotive Works in 1948, to be delivered the following year. Classified H-6, Nos. 1300-1909 were built to essentially the same design as the C&O's 1920 engines of the same class which had reached the end of their service life. However, they featured many of the improvements Baldwin had since applied to its locomotives, including the overfire jets (to improve fuel combustion) visible in this photo taken when the locomotive was new from the builder. At the end of steam operations these newest 2-6-6-2s were stored, and in 1972 No. 1309, the last one built, was donated to the B&O Railroad Museum in Baltimore. In 2014 the locomotive was transferred to the Western Maryland Scenic Railroad, where it is being restored to operating condition.

No. 1309 weighs 434,900 pounds without tender, and when operational will produce 70,773 pounds of tractive effort. Driver diameter is 56 inches and boiler pressure is 210 p.s.i. The high pressure (rear) cylinders measure 27x32 inches, and the low pressure (front) cylinders 35x32 inches. Heat production specifications for No. 1309 include a grate area of 72 square inches, 4825 square feet of evaporative heating surface, and 975 square feet of superheating surface.