The Milwaukee Road's A2 class comprised 47 compound steam locomotives of the 4-4-2 or 'Atlantic' configuration.

The Milwaukee Road acquired them in five batches.

The third batch (A2-b) of five locomotive was built by the Milwaukee Road in its Milwaukee, Wisconsin shops with 85 inches (2.159 m) drivers.

The fourth batch (A2-c) of 12 engines was built by Baldwin as Vauclain compounds with 85 inches (2.159 m) drivers, while the last batch (A2) was for a pair of engines built by Baldwin as balanced compounds.

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