The Pennsylvania Railroad's steam locomotive class D1 (formerly Class A, pre-1895) comprised thirteen 4-4-0 locomotives for express passenger service, constructed at the railroad's own Altoona Works (now owned by Norfolk Southern) during 1868–1872.[3]
They were the first standardized class of locomotives on the railroad and shared many parts with other standard classes.[1]
The PRR was the first American railroad to adopt the Westinghouseair brake, the first tests of which were made in September 1869; Class A locomotives were among those fitted with air brake equipment for those earliest tests.[4][5]
They remained in service until 1945, and were all withdrawn and scrapped by 1946.
^Staufer, Alvin F. & Pennypacker, Bert (1962). Pennsy Power: Steam and Electric Locomotives of the Pennsylvania Railroad, 1900–1957. Staufer. LCCN62020878.
^Warner, Paul T. (1924). Motive Power Development on the Pennsylvania Railroad System. Philadelphia: Baldwin Locomotive Works.