Mate 2
Alaska Railroad MATE 2 photographed in May 1983 at Birchwood scrap line.  Alco RSD1 built as USA #8049 2/43 acquired by the ARR to become #1027 and got four wheel trucks.  Cut down to slug in Mid 1972 and mated with a GP7 in Anchorage Yard.  Retired from active service in 1979 and scrapped in 1984.
 
You might wonder what a Mate is and what it does. Pat Durand explains, "Several railroads used mates in switching service where the locomotives were restricted to yard speeds and never used as Road Switchers. This was an economy move. At low speed the prime mover and generator provide more power than can be delivered with just the traction motors under the locomotive to which the Mate is connected. To increase tractive effort the ALCO Mates provided four more axles with traction motors which were connected to power leads on the GP7L to which they were mated. The economy came from not having to maintain another complete locomotive prime mover, generator and all the controls. That is why they were built from scrap line locomotives. The deck was loaded with a 16" thick slab of concrete for ballast."

 
Photograph courtesy of Ken Brovald, MATI Collection
Museum of Alaska Transportation and Industry
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mate2
Photograph courtesy of Michael Patrick Collection
Anchorage, March 14, 1977
 
Also see Slugs