ALCO RSD-15
The Alco RSD-15 was a diesel-electric locomotive of the road switcher type built by the American Locomotive Company of Schenectady, New York between August 1956 and June 1960, during which time 75 locomotives were produced. The RSD-15 was powered by an Alco 251 16-cylinder four-cycle V-type prime mover rated at ; it superseded the almost identical Alco 244-engined RSD-7, and was catalogued alongside the similar but smaller RSD-12, powered by a 12-cylinder 251-model V-type diesel engine.
The locomotive rode on a pair of three-axle Trimount trucks with all axles powered by General Electric model 752 traction motors. These trucks have an asymmetrical axle spacing because of the positioning of the traction motors. The six-motor design allowed higher tractive effort at lower speeds than an otherwise similar four-motor design.
The RSD-15 could be ordered with either a high or low short hood; railfans dubbed the low short hood version "Alligators", due to their unusually long low noses.
RSD-17
A single example of the very similar model RSD-17 was built by the Montreal Locomotive Works in 1957. After demonstrating on the Canadian Pacific ', the Canadian National ', and the Pacific Great Eastern ', the locomotive was purchased by the Canadian Pacific '. Nicknamed "The Empress of Agincourt", by Pete Fairfull, who was its primary operator for many years, , the locomotive served the railway until 1995, when truck problems forced its retirement.Original owners
| Railroad | Quantity | Road numbers | Notes |
| Atchison, Topeka and Santa Fe Railway | 50 | 800–849 | Low nose |
| Duluth, Missabe and Iron Range Railroad | 6 | 50–55 | Later Bessemer and Lake Erie Railroad 881-886 Cartier acquired the six units 6/1972. All 6 units were converted to low hoods. |
| Pennsylvania Railroad | 6 | 8611–8616 | Later Penn Central 6811–6816. Conrail rebuilt four of them to MT6s 1125-1128. After the dividing of Conrail, 2 went to CSX as 1017 and 1018, and 2 went to Norfolk Southern as 1114 and 1115. |
| Southern Pacific Railroad | 3 | 250–252 | Low nose |
| St. Louis Southwestern Railway | 10 | 5150–5159 | Low nose |
| Canadian Pacific Railway | 1 | 8921 | RSD-17 |
Surviving examples
Six RSD-15s survive in preservation; all are ex-Santa Fe units.Only two are in operating condition; the Austin and Texas Central #442, originally ATSF 842, painted in a modified Southern Pacific "Black Widow" scheme,
and Green Bay and Western Railroad RSD-15 #2407 at the Illinois Railway Museum.
Others that are preserved are Santa Fe 823, in second owner Utah Railway colors at the Utah Railroad Museum, the California State Railroad Museum in Sacramento has one and the Arkansas Railroad Museum has Santa Fe #843.
The RSD-17 demonstrator, Canadian Pacific 8921, is preserved at the Elgin County Railway Museum, St. Thomas, Ontario, Canada.
Models
The RSD-15 has been produced in N scale by Mehano of Yugoslavia.The RSD-15 has been produced in HO scale by Broadway Limited Imports and handmade brass. Alco Models high and Low hoods. Also.
The RSD-15 has been produced in O scale by Atlas O in their Trainman line.
The RSD-17 has not been mass-produced in any scale.