The DL-103 to DL-110 were the first diesel locomotives built by ALCO. The DL only stood for “Diesel Locomotive” and the individual models hardly differed from each other. The odd numbers stood for normal locomotives with cabs (so-called A-units), while the even numbers denoted the cab-less B-units or boosters. As with most American diesel locomotives of the time, the carbody was designed as a self-supporting construction with a streamlined front. The shape of the front with the three-piece windshield was designed by the German-American industrial designer Otto Kohler. All locomotives had an output of 2,000 hp, which came from two six-cylinder inline prime movers with turbochargers. Although four traction motors were sufficient to transmit the power, three-axle bogies, each with a carrying axle in the middle, were used, as in the EMD E series.

A total of 74 A units and four B units were built between 1939 and 1945. By far the largest proportion of these were the 60 A units ordered by the New York, New Haven & Hartford Railroad. All other customers received a maximum of four units, which were often used in front of prestigious passenger trains. The Second World War had made procurement difficult, since the production of purely passenger locomotives was prohibited and locomotives that were equally suitable for freight and passenger trains were also difficult to obtain. Finally, the New Haven only used their locomotives to haul passenger trains during the day, while hauling freight trains at night. Between 1949 and 1951 they were modernized and, among other things, the side windows in the engine room were removed, which were only used for decorative purposes. Despite this, the locomotives' service life was not very long, as they were soon replaced by more modern locomotives. Some were still visually matched to their EMD competitors, but most fell victim to the scrap press in the 1950s.