PRR - Road #: 6736 - 4-8-2 Mountain M1b Steam Locomotive
The M1a's and M1b's are 4-8-2 "mountain" type steam locomotives operated by the Pennsylvania Railroad. Use primarily for hauling freight, many PRR crews regarded the M1's as the pinnacle of the railroad's steam power.
Standout features on both classes are the square-shouldered Belpaire firebox, the 72-inch driving wheels, and a large cross-mounted air tank positioned at the front of the locomotive. The differences between the M1a and M1b classes are minor. The M1b's have firebox circulators that are absent from the M1a's, and the sole visible distinction are the extra cleaning plugs on the firebox sides for maintaining the circulators.