The Pennsylvania built a total of 66 locomotives in its Altoona Works; they operated in semi-permanently coupled pairs.

The conversion of the New York–Philadelphia main line to alternating current in the 1930s saw the remainder of the DD1s scrapped or transferred to the LIRR.

3936 and 3937, is preserved at the Railroad Museum of Pennsylvania and is listed on the National Register of Historic Places.

[2] Each locomotive had its own Westinghouse 315-A, direct current, commutating pole, electric motors within a monocoque cab.

[1] Despite their ungainly appearance, DD1s ran "quietly and smoothly...with no appreciable rod clanking", and had a very low maintenance cost.

A total of 66 locomotives were constructed by the Pennsylvania Railroad's Juniata Shops in Altoona starting in 1909; 3936 and 3937 were put into service in 1911.