ALCO DL420
| ALCO DL420 (S-5 prototype) | 
|  | 
| 
| Specifications |  
| Configuration: 
 |  |  
| • AAR | B-B |  
| Gauge | 4 ft 8 1⁄2 in (1,435 mm) |  | 
| 
| Performance figures |  
| Power output | 800 hp (600 kW) |  | 
| Specifications | 
| Configuration: 
 |  | 
| • AAR | B-B | 
| Gauge | 4 ft 8 1⁄2 in (1,435 mm) | 
| Performance figures | 
| Power output | 800 hp (600 kW) | 
The ALCO DL420 was the prototype ALCO S-5 switcher diesel-electric locomotive.
It was built in August, 1951 using an early six-cylinder 251 engine rated at 800 horsepower (600 kW) and RS-3 subassemblies in its construction. It rode on two-axle trucks, having a B-B wheel arrangement, and was the first ALCO switcher with a front radiator opening. This one-of-a-kind unit spent its time at the Niskayuna, test facility and then at Schenectady as a shop switcher (#6). The unit was scrapped in the late 1950s.
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