Identification
The S-1 and S-3 are distinguishable externally from the very similar S-2 and S-4 1,000 horsepower (750 kW) switchers in that they have a smaller exhaust stack with a round base and a smaller radiator shutter area on the nose sides. The S-1/S-3 radiator shutter area is taller than it is wide, while the S-2/S-4 radiator area is wider. The smaller stack is due to the lack of turbocharging.
The S-10 is not externally distinguishable from later Canadian-built S-3 locomotives; it differed mostly in electrical equipment.
Read more about this topic: ALCO S-1 And S-3