In need of specialized locomotives for its Boston commuter service, the Boston & Albany purchased five 4-6-6T locomotives from Alco in 1928.
The locomotives were designed for rapid acceleration, adequate power for heavy trains of up to 20 cars and perhaps most uniquely – to be operated equally well in either forward or reverse. Not having to turn the locomotives at the end of the line saved space and cost and also a lot of time.
The locomotives bore a strong resemblance to the New York Central's Hudson in the front, with a small attached "tender" behind the cab riding on a shared 6-wheel trailing truck. Coal and water capacity was adequate for the commuter runs. The D1-A class served the railroad and Boston's workers well for two decades before being replaced by diesels. Although these locomotives were unique to the B&A / NYC, there were similar designs used on other railroads with the same needs.