American Locomotive Company introduced the 1,000 horsepower (746 kW) S-4 diesel electric switchers in 1949. Equipped with AAR type A switcher trucks and powered by the ALCO 539 turbocharged, 6-cylinder diesel, several are still in use on short lines throughout the U.S to this day.

Scaled from actual prototype measurements

• Fine scale handrails
  
  
• Separately-applied coupler cut levers, air hoses, piping, etc.
  
  
• Directional LED lighting (includes cab rear headlight)
  
  
• Die-cast hood & chassis for improved pulling performance
  
  
• Dual-flywheels for maximum performance at all speeds
  
  
• Factory-equipped with AccuMate® knuckle couplers
  
  
• Exceptional painting and printing
  
  
• Atlas Master® Gold version features ESU LokSound Decoder