ALCO S-5

ALCO S-5
B&M S-5 #864 in Boston in September 1965
Type and origin Power type Diesel-electric Builder ALCO Serial number 80915–80921 Model S-5 (Specification DL421 and DL421A) Build date June 1954 Total produced 7
Specifications Configuration: ​  • AAR B-B Gauge 4 ft 8+1⁄2 in (1,435 mm) Prime mover ALCO 6-251 Cylinders Straight 6
Performance figures Power output 800 hp (600 kW)
Career Operators Boston and Maine Railroad Numbers 860-865, 909 Locale United States Disposition 1 preserved, remainder scrapped

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).

• List of ALCO diesel locomotives
• List of MLW diesel locomotives

Media related to ALCO S-5 locomotives at Wikimedia Commons

• Sarberenyi, Robert. Alco S5, S6, and SSB9 Original Owners.