During the Second World War, the Soviet Union ordered high-traction diesel locomotives from the USA via the Lend-Lease Act. These should be used primarily in the southern parts of the country, where only little water was available for the operation of steam locomotives. In response, ALCO equipped the RS-1 with two additional powered axles. Despite the same engine power, a higher starting tractive effort was now available, but a decreasing power with increasing speed.
70 RSD-1s were sent to the Soviet Union via the Trans-Iranian Railway, with 12 engines already falling victim to submarines at sea. There they were given the designation ДA20 (DA20), which stood for “Diesel, ALCO, 20 tonnes axle load”. They served there as a basis for the ТЭ1 and its successors. Another 87 locomotives went to the US Army and six to the Ferrocarriles Nacionales de México.
36 RSD-4 were built in 1951 and 1952, based on the RS-3. They had the new 244 series engine with 1,600 hp and were all delivered to US customers. Since the generator was considered too weak, the RSD-5 was built with a new generator from 1952. A total of 167 RSD-5s were built for US customers and 37 for Mexico.
