In 1940, Rock Island approached ALCO and ordered a new type of diesel locomotive that would be equally suitable for switching and road service. Instead of the cab units that were widespread at the time, a locomotive with a load-bearing frame and narrower hoods was developed, also known as the “hood unit”. The resulting design was characterized by the fact that there was an unobstructed field of vision when driving in both directions. This meant that it could be used without restrictions for switching, but also in road service without any cutbacks. It was usually running with the long hood ahead, even if this meant a poorer overview. Thus the new breed of road switchers was created, which was soon adopted by all North American manufacturers.

A total of 466 examples of the RS-1 were completed at ALCO and three more at the Montreal Locomotive Works by 1960. This is the longest production run of any diesel locomotive for the North American market to date, and also meant that they continued in production for several years after their successors were discontinued. The first locomotives, which were actually intended for Rock Island, were delivered to the US Army due to the USA entering the war.

Although a steam generator was available as an option, the RS-1 was rarely used in front of passenger trains. In freight service, with its 1,000 hp, it was primarily used on branch lines. The large six-cylinder ALCO 539T proved to be very durable, with many examples still being used in the 21st century. The RSD-1 and RSC-1 were developed as six-axle developments for lighter rails, with the latter only four axles being driven.

Southern Railway RS-3 No. 2027, together with a combined passenger and baggage car and an EMD FTB converted to a heating car, formed a commuter train in October 1967 in Warrenville, South Carolina

Roger Puta

The RS-2 was built between 1946 and 1950, with 368 examples being built at ALCO and nine in Montreal. It differed from the RS-1 mainly in the new 244 series V12 engine with 1,500 hp and a slightly more rounded body. The new prime mover did not prove to be as reliable in use as the old one. 64 pieces were delivered to Mexico and 46 to Brazil. The locomotives for Brazil had a gauge of 1,600 mm.

The RS-3 achieved the highest number of units, of which 1,272 were built between 1950 and 1956, with 146 units coming from Montreal. It was created at a time when Fairbanks-Morse and Baldwin were also bringing their road switchers from 1,500 to 1,600 hp to keep up with competitor EMD. 98 engines went to Canadian customers and 46 to Brazil. Here, too, a six-axle variant with four powered axles was developed as the RSC-3.

To overcome the reliability problems of the 244 series prime mover, 98 RS-3s were rebuilt between 1972 and 1978 with EMD 567 engines. The engines, including the fan system, came from decommissioned EMD E8s. These were named RS-3m to distinguish them. A few of these are still in use in 2022, although some RS-3s that have not been converted have survived into the 21st century.

To change secondary lines in New South Wales from steam to diesel, AE Goodwin built the DL531 under ALCO license. With six axles, this had a weight of only 74 tons and a six-cylinder with 1,050 hp. Until 1970, the NSWGR received a total of 165 locomotives in standard gauge, which it designated as class 48. Otherwise it was also known as RSD8.

The South Australian Railways also bought 45 DL531 in three different gauges and designated them as class 830. The Silverton Tramway bought three, and customers were also found in Brazil, Peru and Pakistan. In Australia, many were retired from the state railways in the nineties and sold to private railways, many of which are still in use today.

The DRS-6-4 series included road switchers that had a total of six axles, four of which were powered. The three less powerful variants each had a six-cylinder with 660, 750 or 1,000 hp, with only the most powerful variant having a turbocharger. 

SNCF A1AA1A 62030 in September 1983 at Bobigny depot

Didier Duforest

The first variant with 660 hp was manufactured from 1946 and 100 of the 106 locomotives went to the SNCF. They were derived from the four-axle VO-1000 and had a carrying axle in each bogie to reduce the axle load. They were given the designation A1AA1A 62000 and remained in service until 1994. The remaining six went to Morocco.

Sectional drawing of the DRS-6-4-660NA

Didier Duforest

The DRS-6-4-1000 received the same six-cylinder engine as the 660 hp variant, but here it delivered 1,000 hp thanks to a turbocharger. From 1948, 20 of this variant were delivered to Algeria on behalf of France. In 1949 a single naturally aspirated 750 hp locomotive was delivered to Morocco and used to transport phosphate.

The variant with 1,500 hp was powered by an eight-cylinder with turbocharger and was also available from 1946. In the USA it was replaced by the AS-416 in 1950. The DRS-6-4-1500E was manufactured for export until 1952. Ultimately, more than half of a total of 91 DRS-6-4-1500 were sold to Algeria, Morocco and Tunisia.

By upgrading the G12 with the new 645 series engine, the G22 was born, which was again built in a wide variety of variants for customers in the first, second and third worlds. Using a non-turbocharged engine has increased reliability and simplified maintenance. The locomotives were available with different gauges and with two- and three-axle bogies. The six-axle variants were available with either the “C” model designation with six traction motors or the “4” model designation with the (A1A)(A1A) wheel arrangement. Steam heating was available as an option. In later variants, the modular electronics of the “Dash 2” were installed, these can be recognized by the suffix “-2”.

As an alternative to the reconstruction measures of older road switcher locomotives, EMD has been offering the GP15-1 since 1976. It was a short four-axle vehicle with a 1,500 hp twelve-cylinder prime mover that did not have a turbocharger. These locomotives could be used inexpensively for light road or switching service and a total of 310 were built by 1982. Of these, 160 went to the Missouri Pacific Railroad, which was bought by the Union Pacific shortly thereafter. Another 100 went to Conrail and 25 each to the Chicago and North Western and the St. Louis-San Francisco Railway.

After the end of production, the GP15T was presented, which was identical in dimensions and power to the GP15-1. The difference was that the prime mover used was a smaller turbocharged eight-cylinder. Due to the same power with a smaller displacement and a lower number of cylinders, this engine could be used more economically. Chessie System with 25 engines and Apalachicola Northern with three more were found as buyers. As the lower maintenance costs and higher reliability of a non-turbocharged engine were more important to many operators at the time, no further GP15Ts were built.