Pennsylvania classes D and Da

For the transport of freight trains, the PRR had Baldwin build a class of ten-wheelers from 1868, which was one of the heaviest designs of this manufacturer at the time and achieved a very respectable number for its time. Baldwin made 241 between 1868 and 1873 and the PRR's own workshops added 45 more by 1875.

Since there wasn't much space between the bars of the bar frame, a narrow, deep firebox had to be accommodated. For this reason, the distance between the second and third driving axles was chosen to be significantly larger than that between the first and second, in order to be able to realize a greater length of the firebox. Since the grate area was still relatively modest for the size of the locomotive, good hard coal was used for firing. In order to avoid problems when running through curves with the large wheelbase, the first driving axle was designed without wheel flanges.

Between 1878 and 1882, 157 of the locomotives were rebuilt to the Da class, which was to be used to haul heavy, slow trains. To ensure this, the diameter of the drivers was reduced from 56 to 50 inches. At the same time, the service weight increased by about five tons. Other non-rebuilt locomotives were instead sold to several smaller railroads.