If I recall correctly the reason for the design of the camelback locomotive was to carry a very large Wootten (post Civil War) firebox on whose wide grate the locomotive could burn culm anthracite coal rather than the more common and smoky bituminous. The Northeastern railroads with access to anthracite (the fields were in the Northeast) were the ones to use them. The Reading, Jersey Central, DL&W, L&NE, and the B&O were the biggest users of them. The railroads might be hauling bituminous in their cars for the iron foundries but were burning anthracite in their camelback locomotives when they could get it (the USN wanted it, too to reduce their smoke signature).