4 ft 8+1⁄2 in (
1,435 mm)
| Prime mover | Alco 251 |
|---|
| Cylinders | Straight 6 |
|---|
| Performance figures |
|---|
| Power output | 800 hp (600 kW) |
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The Alco S-5 (DL 421A) was a diesel-electric switcher locomotive rated at 800 horsepower (600 kW), that rode on two-axle trucks, having a B-B wheel arrangement.
This was Alco's second attempt to build a replacement 251-engined switcher to replace the 539-engined S-3 and S-4. Only seven were sold. The demonstrator unit was ALCO specification DL421 and the six production units were ALCO specification DL421A. Alco fitted the 251A engine in its replacement, the S-6 with power output raised by 100 horsepower (75 kW).
Original owners
| Railroad | Quantity | Road numbers | Notes |
| Alco (demonstrator) | 1 | 909 | to Island Creek Fuel and Transportation Company #102 |
| Boston and Maine Railroad | 6 | 860–865 | |
See also
External links
Media related to ALCO S-5 locomotives at Wikimedia Commons
- Sarberenyi, Robert. Alco S5, S6, and SSB9 Original Owners.
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Media related to ALCO S-5 locomotives at Wikimedia Commons 
