Well over 1,300 RS-3 road-switcher locomotives were built by ALCO between 1950 and 1956. It can be considered one of the most successful four-axle diesel road-switchers ever produced by the builder. These 1,600hp locomotives were powered by an ALCO 244 V-12 engine which was complimented by rugged GE electrical components. The RS-3 was truly a versatile locomotive. It could be found in virtually every type of service from passenger and commuter runs to heavy-haul and local freight assignments. Original owners of the RS-3 tended to be in the eastern and central regions of the US (with heavier concentrations in the northeast and southeast).

During this same time-period, ALCO offered a six-axle road-switcher which was more commonly found in the west. The RSD-4/5 was externally very similar to the RS-3, having six-axle trucks as an obvious spotting feature. They produced the same 1,600hp as an RS-3, but offered increased tractive effort due to the use of a larger generator. Many RSD-4/5s were assigned to operate in mountainous territory (with varying degrees of success) on the Southern Pacific, Santa Fe and the Utah Railway.

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