There were three different specifications issued that covered the RSD-1 model; E1645 and E1646 were for wartime production for the US Army, while E1641 was a post-war order for the Mexican National Railways (Ferrocarriles Nacionales de México).
Seventy of the RSD-1s were shipped overseas to the Soviet Union during World War II, where they were classed as the Soviet Railways Да20 (Da20) class, as part of the Allied war effort. These locomotives were also used on the Trans-Iranian Railway. The Soviets subsequently kept many of the RSD-1s after the war, adopting the design to form the basis of their own line of diesel locomotives. A dozen RSD-1s were sunk en route to the Soviet Union when the ship they were on was torpedoed by a Nazi Submarine.
The first 13 RS-1s were requisitioned by the US Army, returned to ALCO and rebuilt to RSD-1s #8000-8012 for use on the Trans Iranian Railroad. This effort was to supply the Soviet Union. See the RS-1 article for the identity of the first 13 RSD-1s.