The first two class AA1 electric locomotives were not convincing, as their running smoothness was insufficient due to the lack of leading axles. For this reason, the PRR took the 4-4-0 wheel arrangement that was so popular in the USA for steam locomotives as a reference and ordered an electric locomotive with a 2-B wheel arrangement from Baldwin. Locomotives with this wheel arrangement were classified as class D on the PRR, which is why the one-off was given the designation “Odd D”. Although the entire mass of the locomotive was no longer available as adhesive weight, the leading bogie improved stability at higher speeds.

In contrast to its predecessors, it was operated under 11.000 V AC and had a pantograph on the roof. A section of the route was electrified with this system for the test run. The traction motors were no longer directly connected to the axles, but were sprung via a quill. In test operation on the Long Island Railroad, it proved to be quite suitable for higher speeds. With a wheel diameter of 72 inches, it could reach speeds of up to 85 mph while still remaining steady and controllable. In the other direction of travel, however, the running smoothness was no longer so outstanding, since then it didn't have leading axles anymore. As a result of this experience, the DD1 class locomotives were soon ordered, which basically looked like two Odd D coupled together and were intended for operation with direct current from the conductor rails.