| PRR D2 & D2a | |
| Powertype: | Steam |
| Builder: | PRR Altoona Works |
| Builddate: | 1868–1872 (D2); 1881–1882 (D2a) |
| Totalproduction: | 20 (D2); 45 (D2a) |
| Whytetype: | 4-4-0 |
| Uicclass: | 2′B |
| Leadingdiameter: | 280NaN0 (D2) 300NaN0 (D2a)[1] |
| Driverdiameter: | 620NaN0 (D2) 680NaN0 (D2a) |
| Wheelbase: | 22feet |
| Length: | 54feet[2] |
| Width: | 9feet |
| Height: | 14feet (D2) 14feet (D2a) |
| Weightondrivers: | 525001NaN1 (D2) 537501NaN1 (D2a) |
| Locoweight: | 805001NaN1 (D2) 822001NaN1 (D2a) |
| Tenderweight: | 514001NaN1 (D2 & D2a) |
| Locotenderweight: | 1319001NaN1 (D2) 1336001NaN1 |
| Tendertype: | Eight-wheel with water scoop |
| Fueltype: | Soft coal |
| Fuelcap: | 80001NaN1 |
| Watercap: | 2400usgal |
The Pennsylvania Railroad's steam locomotive class D2 (formerly Class B, pre-1895) comprised twenty 4-4-0 locomotives intended for mountain passenger helper service, constructed at the railroad's own Altoona Works (now owned by Norfolk Southern) during 1869–1880.[3] They were the second standardized class of locomotives on the railroad and shared many parts with other standard classes.[4]
This design differed from the Class A (later D1) mainly in its smaller drivers for greater tractive effort in mountainous terrain. Like all the early standardized 4-4-0s on the PRR, the Class B had a wagon-top boiler with steam dome and a firebox between the two driving axles.
In 1881, the PRR took the Class B design and modified it to produce more locomotives for express passenger service, with 680NaN0 drivers like the earlier Class A. These new locomotives were designated Class B A, and were classified as D2a in the post-1895 scheme; forty-five of them were constructed.[5]
