However, beyond this, their design was largely similar - aside from the PA/PB's both being larger A1A-A1A types with an even more striking nose - and many railroads used PA and FA locomotives for both freight and passenger service.

This unusually-short testing sequence was brought about by the decision of ALCO's senior management that the engine and an associated line of road locomotives had to be introduced no later than the end of 1946.

In September, 1946, the first production units, an A-B-A set of PA1s in Santa Fe colors, numbered #51L, 51A and 51B, were released from the factory and sent to New York's Waldorf-Astoria Hotel, which had a private railroad siding, for exhibition before being launched into road service.

Fans deemed the PA one of the most beautiful diesels and an "Honorary Steam Locomotive", as noted by Professor George W. Hilton in a book review in September, 1968 Trains Magazine.

When accelerating, until the turbocharger came up to speed, thick clouds of black smoke would pour from the exhaust stacks due to turbo lag.