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. Assigned to class S-1, these behemoths were outshopped by Baldwin and Lima in 1923-24. The example 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. 510, originally No. 6132, is seen here at Willard, Ohio, on March 31, 1957, in a transparency by an anonymous photographer provided by Edward Lorence. For dimension of the S-1 class consult the commentary for No. 6137 (512) following.