Always known for its independent engineering and distinctive style, the Pennsylvania Railroad produced many notable steam locomotives. The M1 4-8-2s certainly rank among their most successful designs.
The Pennsy had already found its primary passenger power in the form of the K4 Pacific. A design perfected over decades of engineering and revision, 425 K4s provided one of the largest stables of passenger locomotives to be found anywhere. As good as they were however, the K4s still had their limits. As passenger trains grew longer and heavier in the 1920s, the railroad was forced to double and even triple-head the Pacifics over its mountain grades. Larger power was needed.
Appropriately, the solution for the problem would come in the form of a Mountain-type (4-8-2) locomotive…
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