By the mid 50s, increasing pressure from long-haul trucks, declining passenger revenues and mounting costs forced western railroads to find new ways to improve service. Faced with expensive overhauls of early cab and hood unit diesels, many began looking at new equipment as well as ways to improve existing motive power. In 1955 Union Pacific equipped several GP9s with turbochargers as an experiment. Their success inspired EMD to create its own turbocharger for the 567 prime mover, leading to the introduction of the six-axle SD24 in 1958. Further experiments in 1959 created a four-axle version, dubbed the GP20. Western Pacific was impressed by the new model's ability to deliver maximum horsepower at various altitudes and ordered the first six. Early in their careers, the new units were typically assigned priority freights. The 1960s were a period of change; both Santa Fe and New York Central adopted simpler paint schemes, and the arrival of newer power bumped them into secondary service. Many were repainted and renumbered for their new owners, and spent their last years in local and yard service. Following their retirement, a few went to work for shortline operators.

STANDARD FEATURES:

* Protoype Specific Details
* Retooled Handrails & Other Parts for More Accurate Detail
* Over 135 Factory-Applied Parts
* Heavy Diecast Chassis
* 5-Pole Motor with Skew Wound Armature
* Precisely Meshed Worm Gear & Spur Teeth for Silent Running
* LED Directional Headlights
* Proto MAX Magnetic Knuckle Couplers

UP SPECIFIC FEATURES:
(Phase 1a) From approx. mid 1970s - early 1980s

• Dynamic brakes
• Winterization hatch
• Small beacon (non-operating)
• Left cab side air filter
• Raised Leslie S-3L horn
• Correct truck journal bearings