Until the advent of the less than totally successful Q2 duplex drive freight engines in the mid-1940s, fast freight and general merchandise duties on the Pennsylvania Railroad typically fell to the 301 M1 and M1a Mountain types. These 4-8-2s often handled heavy passenger or mail trains as well. No. 6747, shown here in an unattributed photo, belonged to the M1a group, being a 1930 product of Baldwin Locomotive Works, the PRR's favored builder outside of its own Juniata shops. These locomotives had 72-inch drivers and 27x30-inch cylinders. They carried 250 pounds per square inch of boiler pressure, having 4698 square feet of evaporative heating surface and 1634 square feet of superheating surface. They developed 64,550 pounds of tractive effort and weighed 390,000 pounds. No. 6747's 12-wheel tender has the head breakman's shanty atop the water compartment, a feature common in Pennsylvania Railroad practice. Many of the M1 engines boasted the larger 16-wheel "coast-to-coast" tender like 2-10-4 No. 6450.