The Alco S-5 (DL 421A) was a diesel-electric switcher locomotive rated at , 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 .
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 List of ALCO diesel locomotives List of MLW diesel locomotives
External links
Sarberenyi, Robert. Alco S5, S6, and SSB9 Original Owners.