Alco introduced the S-4 in 1950. The S-4 like the earlier S-2 was a 1000 horsepower switcher. Some 636 S-4’s were built for North American railroads. The primary quick spotting difference between the S-1/S-2 and the S-3/S-4 can be seen in the trucks. The S-1/S-2 has Blunt trucks, while the S-3/S-4 has AAR-style trucks. The versatility of the S-2’s and S-4’s were evidenced by their service in mainline railroads, shortlines, and industrials.

Features Include:
Newly tooled with improved cab design
5-pole skewed armature motor for reliable operation
Dual-flywheels for maximum performance at all speeds
Factory-equipped with AccuMate® knuckle couplers
Exceptional painting and printing
Sturdy die-cast mainframe and gear cases