These locomotives were of 2-8-2 wheel arrangement in the Whyte notation, or 1′D1′ in UIC classification.

A total of 233 locomotives were built to this plan for the USRA; postwar, it became a de facto standard design, which was built to the total of 957 locomotives including the USRA originals and all subsequent copies.

[2] Heavy Mikado used the same running gear as the USRA Light Mikado but were built to a higher axle load, larger cylinders and a much larger boiler for more power and steam-generating ability.

Many aspects of the PRR L1s class were carried over to the Heavy Mikado, although not that locomotive's distinctive Belpaire firebox.

[1] None of the originals built under USRA auspices or any of the subsequent copies were preserved.