The Alco S-6 was a diesel–electric switcher locomotive 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.
Design
Visually indistinguishable from the S-5, the S-6 used an ALCO 251A or 251B prime mover rated at . The locomotive rode on two-axle AARtrucks, giving a B-B wheel arrangement. ALCO produced a cow–calf variant for the Oliver Iron Mining Company designated SB-8/SSB-9, two sets were produced of this version. == Original owners ==