May 1955–December 1960
The Alco S-6 (specification DL 430) was a diesel-electric locomotive of the switcher type constructed by ALCO of Schenectady, New York; a total of 126 locomotives were built between May 1955 and December 1960. The S-6 was an improved version of the earlier S-5.
ALCO S-6 Wikipedia
Visually indistinguishable from the S-5, the S-6 used an ALCO 251A or 251B prime mover rated at 900 horsepower (670 kW). The locomotive rode on two-axle AAR trucks, giving a B-B wheel arrangement. ALCO produced a cow-calf variant for the Oliver Iron Mining Company designated SB-8/SSB-9.