With its older E-units reaching the end of their serviceable lives, Seaboard Air Line asked EMD for a passenger version of the SD35 that could double as a freight unit, especially if passenger trains continued to be discontinued. EMD came up with the SDP35, and SAL placed an order, trading in E4 and E6 units. The first of SAL's new SDP35s was delivered in summer 1964.
The SDP35 wound up going to four railroads: SAL (20, numbered 1100-1119), Atlantic Coast Line (1, numbered 550), Louisville and Nashville (4, numbered 1700-1703) and Union Pacific (10, numbered 1400-1409).
Although SAL successfully used the SDP35 in high speed passenger service as well as on expedited freight and piggyback trains, Union Pacific found it unsuitable and relegated its entire fleet to freight service while its famous yellow E-units continued to handle passengers.
|Seaboard Air Line Railroad|| ||1100–1119||to Seaboard Coast Line Railroad|
|Atlantic Coast Line Railroad|| ||550|
|Louisville and Nashville Railroad|| ||1700–1703|
|Union Pacific Railroad|| ||1400–1409|