By 1935 the PRR had two classes of main line electric locomotives in service: 58 GG1s and the P5a class. The GG1s were used for passenger service. The less successful P5a locomotives were hauling freight. The PRR wanted a dual passenger-freight electric locomotive and developed a 2-B+B-2 that incorporated the best features of the previous electric locomotives. The Altoona Shops built a single prototype of this husky streamlined 4-4-4-4 Class DD-2 and outshopped it in 1938. The 72' - 6" hybrid was given road number 5800 and was put to test.

The Class DD-2 had 62" drivers (powered by 625 HP motors like the Class R-1) and an articulated frame like the GG1 (for better tracking) and a welded carbody. It employed quill drive and with its freight gearing (21 to 83 ratio) had a maximum speed of 70 mph and with passenger gearing (28 to 76 ratio) was designed for 100 mph. The DD-2 was tested with freight gearing and was never geared for passenger service. This 450,000 lbs locomotive was rated at 5000 HP and exerted 71,500 lbs of tractive effort.

The DD-2 was a very good electric locomotive, but it just wasn't that much better than the GG1. With the GG-1 fleet at 72 units by 1938, it was decided that more GG1s would be built and thus avoid having yet another class of electric locomotive on the railroad. After testing, the single example of the Class DD-2 stayed in service. It was often used as the Baltimore Tunnel Helper and for many years it hauled local freight trains between Wilmington, DE and Philadelphia, PA. It was scrapped in 1962.