Pennsylvania class D

In principle, the PRR class D can be described as the first Moguls, but the leading axle was fixed in the frame. The driving axles with small wheel diameters were well spaced within the frame. The tender already had four axles, but only the first two were in a movable bogie and the rear ones were fixed in the frame.

Although the locomotives were generally described as being a good design, the smooth running was apparently not entirely convincing. This is the way to explain why the chassis was later rebuilt. Some locomotives were rebuilt to 4-4-0 with larger wheels. A third driving axle was installed later again, resulting in a 4-6-0 wheel arrangement. They were scrapped in the late 1860s.