The American Locomotive Company pioneered the multi-purpose "road switcher" design in 1941 with its 1000 hp RS-1. Alco's designers added a second, shorter hood to a basic switcher to make room for a steam boiler for passenger train heat. The short hood also afforded the crew additional accident protection. Smoother-riding trucks made Alco's new design suitable for the higher road speeds that would be daunting in a typical switcher.

In 1946, Alco cataloged the first six-axle version of its road switcher, the RSC-2. Designed for operation on the lighter rail found on branch lines and short lines, the engine used two more axles to spread out its weight. The trucks were a so-called "A1A" configuration: the two end axles had traction motors while the middle wheels were unpowered idlers.

In 1951, the Chicago and North Western asked Alco to build a six-axle version of its RS-3, this time with all axles powered. The body and the 1600 hp Alco 244 prime mover were the same as used in the RS-3, but the additional traction motors gave the new model RSD-4 stronger low-speed performance. The longer trucks were both smooth-riding and more suitable for lighter rail. The design proved to be a winner, and a dozen railroads purchased the RSD-4 and its near-identical twin, the RSD-5, which sported an improved GE generator.

2018 Volume 2 Catalog

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