During the decade of the 1950s, American locomotive manufacturers introduced 28 different road-switcher models: Alco (11), Baldwin (7), EMD (6), Fairbanks-Morse (3) and GE (1); they came in four-axle, as well as six-axle configurations. Fairbanks with its "Trainmaster" had been the first to reach the 2400-hp plateau. However, it did not take EMD nor Alco long to regain their lead in the horsepower race, with the SD24 and RSD15 models respectively. In addition, Alco and GE had 2400/2500-hp four-axle demonstrators on the road before the decade drew to a close. Alco's five new 2400-horsepower RS27 sales ambassadors hit the road in December 1959, and GE's U25Bs demos closely followed.

Alco's RS27 (specification DL640) was designed to handle high-speed freights; it was not intended to be a general purpose locomotive. As such,it was powered by the 16-cylinder version of the 251B engine, rated at 2400 horsepower. The new model was built on the same foot-print as the RS-11; the cab was pushed forward on the frame too make room for the elongated engine block with its four additional cylinders. The locomotive sported a stubby nose and "picture window" windshield. The end result was distinctive, but would barely move the needle on an aesthetic scale. Beyond Alco's five-unit demonstrator set, only 22 other four-motor RS27s were produced; they went to the C&NW (#900-903), GB&W (#310) PRR (#2400-2415), Soo (#415 & 416). Additionally, Union Pacific opted to purchase four of the demonstrators after their tour had completed; they became UP #675-678. Alco Demonstrator #640-1 instead was rebuilt as a new Century 424 and delivered to PRR as #2415.

Photographer Don Kalkman captured the above scene at a sanction photo shoot at the Midway roundhouse on 29 April 2016.