The Pennsylvania Railroad's steam locomotive class D3 (formerly Class C, pre-1895) comprised sixty-seven 4-4-0 locomotives intended for general passenger and freight service, constructed at the railroad's own Altoona Works (now owned by Norfolk Southern) during 1869–1881.^[2] They were the third standardized class of locomotives on the railroad and the most numerous of the early standard types; they shared many parts with other standard classes.^[3]

This design differed from the Class A (later D1) mainly in its smaller drivers for greater tractive effort for freight haulage. Like all the early standardized 4-4-0s on the PRR, the Class C had a wagon-top boiler with steam dome and a firebox between the two driving axles.^[2][4]