Alco RSD12 Builder List and Phases

RSD12 Roster Index | RSD12 Phases

Alco RD12 - Ferrocarril del Pacifico 510 at Guadalajara, Jalisco, December 24, 1964. Photographer: R.W. Bierman
Alco RD12 – Ferrocarril del Pacifico 510 at Guadalajara, Jalisco, December 24, 1964. Photographer: R.W. Bierman


  • Phase Ia – April, 1956 to November, 1958 – original carbody. Brake wheel is located in a recessed mount on the front of the short hood. A prominent intercooler is protected by a box above the door line near the radiator. Engine air and electrical equipment ventilation is provided by three closely spaced square openings behind the cab. If the locomotive is equipped with dynamic brakes, there are three additional openings between the engine air intakes and the intercooler, under the dynamic brake hatch on the roof, over the prime mover. On the top of the radiator shutters is a small rectangular box housing an actuator to control the shutters. The buffer (coupler box) is a heavy rectangular casting.
  • Phase Ib – October to November, 1959 – actuator box eliminated on radiator shutters.
  • Phase Ic – December, 1959 to April, 1961 – buffer (coupler box) changes to a sloped, teardrop shaped casting
  • Phase IIFebruary, 1962 to October, 1963 –  a new carbody is adopted that will be carried over to the RS32 and RS36. The prominent exterior intercooler is eliminated and is now inside the carbody. Three rectangular openings above the door opening – that have been there all along to provide air to the turbocharger cooler – are now exposed. The brake wheel no longer is recessed.

Builder List

YearMonthRailroadOrderBuilder NoPhaseQty
1956AprilChesapeake & Ohio 6700-6701S327081943-81944Ia2
1956AprilChesapeake & Ohio 6704-6708S327081947-81951Ia5
1956MayChesapeake & Ohio 6709S327081952Ia1
1956JuneLake Superior & Ishpeming 1801-1802S327081953-81954Ia2
1956AugustChesapeake & Ohio 6702-6703S327081945-81946Ia2
1957FebruaryNickel Plate Road 325-327S327081955-81957Ia2
1957MayNickel Plate Road 328S327081958Ia1
1957JuneNickel Plate Road 329-332S3270819659-81962Ia4
1957JuneNickel Plate Road 333S328582378Ia1
1957DecemberPennsylvania Railroad 8655-8656S328582379-82380Ia2
1958JanuaryPennsylvania Railroad 8657-8663S328582381-82387Ia7
1958FebruaryPennsylvania Railroad 8664-8670S329882066-82072Ia7
1958MarchPennsylvania Railroad 8671-8678S329882073-82080Ia8
1958AprilPennsylvania Railroad 8679S329882918Ia3
1958JulyNacionales de Mexico 7400-7401S329882919-82920Ia2
1958SeptemberFerrocarril del Pacifico 1502S329882921Ia1
1958NovemberFerrocarril del Pacifico 1503S329882922Ia2
1958NovemberFerrocarril del Pacifico 1504-1508S330983339-83343Ia5
1959OctoberFerrocarril del Pacifico 509-510S332283545-83546Ib5
1959NovemberLake Superior & Ishpeming 1803S332283547Ib1
1959DecemberNacionales de Mexico 7402-7404S332283548-83550Ic3
1960JanuaryNacionales de Mexico 7405S332283551Ic1
1960FebruaryFerrocarril del Pacifico 511-512S333083636-83637Ic2
1960MarchNacionales de Mexico 7406-7408S332283552-83554Ic3
1960MarchNacionales de Mexico 7409-7410S333083626-83627Ic2
1960AprilNacionales de Mexico 7411-7415S333083628-83632Ic5
1960MayNacionales de Mexico 7416-7417S333083633-83634Ic2
1960JuneNacionales de Mexico 7418S333083635Ic1
1961JanuaryFerrocarril del Pacifico 513-514S333083638-83639Ic2
1961FebruarySouthern Pacific 7000-7005S333083640-83644Ic6
1961FebruarySouthern Pacific 7006-7009S333783836-83839Ic4
1961MarchSouthern Pacific 7010-7020S333783840-83850Ic11
1961MarchNacionales de Mexico 7419-7423S333783851-83855Ic5
1961AprilNacionales de Mexico 7424-7428S333983806-83810Ic5
1961AprilNacionales de Mexico 7429-7440S333983956-83967Ic12
1962FebruaryFerrocarril del Pacifico 515-517S333983968-83970II4
1962MarchFerrocarril del Pacifico 518-520S344784080-84082II2
1962AugustNacionales de Mexico 7441-7457S334784083-84099II17
1962AugustNacionales de Mexico 7458S335284279II1
1962SeptemberNacionales de Mexico 7459-7472S335284280-84292II14
1963OctoberLake Superior & Ishpeming 1804S335284293II1


Some Nacionales de Mexico units (along with contemporary RS11 deliveries) have a modified buffer. This was not used on the Ferrocarril del Pacifico orders, as far as it is possible to see, because they used a semi-round pilot added by the railroad after delivery that covers the buffer entirely. Known units affected are NdeM 7419-7440 and 7459-7472. Units known to have standard buffers are NdeM 7402-7404 and 7418.


  • Nickel Plate Road Historical Society – Nickel Plate Road diesel locomotive roster
  • John R. Signor and John A. Kirchner, The Southern Pacific of Mexico and the West Coast Route, Golden West Books, 1987, pg 157
  • Larry Russell, Dan Dover, and Dick Will, “Ferrocarriles Nacionales de Mexico – NdeM Diesel Roster,” Extra 2200 South, March-April, 1974 (Issue 45), pg 22
  • John D. Hahn, Jr., Pennsylvania Railroad Diesel Locomotive Pictorial, Volume 1: Alco RS Series, Withers Publishing, 1995, pg 49
  • Joseph A. Strapac, Southern Pacific Diesel Locomotive Compendium, Volume 1: Pre-1965 SP Numbers, T&NO and Cotton Belt Subsidiary Railroads, Shade Tree Books, 2004, pg 120
  • Dr. David Peck, “Alco’s RSD-12,” Mainline Modeler, September, 1987, pgs 61-64