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ALCO S-5 Diesel-Electric Switcher Locomotive
The Alco S-5 (DL 421A) was a diesel-electric locomotive of the switcher type 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: Alco (demonstrator)
Quantity: 1
Road numbers: 909

Notes: to Island Creek Fuel and Transportation Company No. 102.

Railroad: Boston and Maine Railroad
Quantity: 6
Road numbers: 860–865

ALCO S-5 Overview
Type and origin
Power type: Diesel-electric
Builder: ALCO
Serial numbers: 80915–80921
Model: S-5 (Specification DL421 and DL421A)
Build date: June 1954
Total produced: 7
Specifications
AAR wheel arrangement: B-B
Gauge: 4 ft 8 1⁄2 in (1,435 mm)
Prime mover: ALCO 251
Cylinders: Straight 6
Performance figures
Power output: 800 hp (600 kW)

See also:

Alco Diesel Locomotives

Diesel Locomotives

Locomotives

Boston & Maine ALCO S-5 No. 864 in Boston in September of 1965.  Photo by Roger Puta.

Boston & Maine ALCO S-5 No. 864 in Boston in September of 1965. Photo by Roger Puta.
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