The Baltimore & Ohio's 2-10-2s were known as the "Big Sixes" because of their size, and because their original numbers were in the 6000 range. Although renumbered to 512 in the late 1950s, the locomotive shown here reveals its "Big Six" heritage in the length of its wheelbase, which required two sand domes atop the boiler to assist traction on the heavy Appalachian grades that were part of these engines' original territory. No. 512 (original number uncertain, but between 6133 and 6140) was a member of class S-1, outshopped by Baldwin and Lima in 1923-24. They featured 220 p.s.i. of boiler pressure and 30x32-inch cylinders, and their 64-inch drivers were so well counterbalanced that they proved to be faster locomotives than the typical "drag freight" 2-10-2 of their era. They weighed 436,000 pounds and mustered 84,150 pounds of tractive effort. Their evaporative heating surface totaled 5250 square feet, with 1510 square feet of superheater surface, and they had a grate area of 88 square feet. Robert Leffingwell snapped this transparency at the B&O facility in Garrett, Indiana on March 21, 1957. No examples of this famous design have been preserved.