The B&A's class D-1a 4-6-6T double-enders were erected by the American Locomotive Company in 1928. They had 23½x25-inch cylinders and a boiler pressure of 215 p.s.i. Weighing 352,000 pounds, they produced a tractive effort of 41,651 pounds. With a grate area of almost 61 square feet, they had 2761 square feet of evaporative heating surface and 788 square feet of superheater surface. The 63-inch drivers of both classes of B&A double-enders, though small for locomotives in passenger service, helped them get their trains moving more quickly after their frequent station stops (although the driver diameter of the D-1a class was later raised to 64 inches). In this image of unknown origin No. 404 of the class rests at Boston's Beacon Park terminal sometime between 1940 and 1951, when it was sold for scrap.