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Locomotive Descriptions and Phases - ALCO/MLW C-420, C-424, C-425

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CP #4237, an MLW C-424 preserved at Exporail near Montreal, seen in 2004.

By the early 1960s, ALCO's road locomotive designs were starting to show their age. While ALCO had kept up with contemporary horsepower increases, their recent models had started to fall behind the EMD GP30 and newly introduced GE U25B in both sales and features. The hodge-podge of model names and specifications highlighted the incremental changes from previous models; at the time, their main offerings included the 1,800 hp RS-36 and 2,000 hp RS-32 (both derived from the RS-11), the 2,400 hp RS-27, and the 6-axle RSD-12 and RSD-15 (1,800 and 2,400 hp respectively).

As a result, in 1963 ALCO proceeded with the first major redesign of their road locomotives, designated the Century series. A thoroughy modern design, they incorporated several key improvements over previous models:

ALCO promoted the reduction in operating costs made possible by these improvements. The model names followed a logical format, with "C" for the Century series followed by the number of axles and the first two digits of the horsepower. At the start of production, the 4-axle C-420 and C-424 and the 6-axle C-624 were cataloged, replacing the RS-32, RS-27 and RSD-15 respectively; the C-624 was promptly uprated and replaced by the C-628 before any were built.

The 251 engine (introduced in 1956) and GE electrical components were carried over from previous models. On 4-axle units, the dynamic brakes were contained in a housing along the top of the engine compartment similar to earlier models, with rectangular intakes above the engine compartment doors. The inertial air intakes were located immediately behind the cab, and the radiators were at the rear with large louvered intakes on the bottom half of the hood.

Aesthetically, the Century series was characterized by a pointed cab front, a clean-lined hood, and narrow ladders at the corners in place of steps. On most units the rear hood corners were notched for the numberboards. In addition to many shared hood components, the initial models also shared a similar underframe design with the same walkway height, pilots and steps.

While several later Century models further pushed the envelope in features and horsepower at the time, the Century series wasn't enough to reverse ALCO's declining sales, and the company ceased locomotive production in 1969. However, the locomotives themselves ultimately proved to be fairly solid performers, with many in service for over 20 years and a handful remaining in regular use after 2000. After ending production ALCO sold the designs to MLW, who used them as the basis for new M-line models up to the 1980s.

Model Descriptions


Mechanically similar to the previous RS-27, the C-424 was powered by a 16-cylinder 251 engine rated at 2,400 horsepower supplying a GE generator and traction motors. The trucks were the standard drop-equalized "Type B" used on earlier ALCO models. While the underframe was lengthened by more than 2 feet over the RS-27 (to 59' 4" over the coupler pulling faces) the long hood was lengthened by almost 4 feet, so the short hood remained stubby. Intended as a freight-only model, there was no room for a steam generator.

The C-424 was not a big seller domestically but met with some success in Canada and Mexico. Almost half of ALCO's production (45 of 98 units) went to NdeM in Mexico, and MLW production in Canada nearly matched ALCO's output, with 92 units sold to CN and CP. Of the initial models in the Century series, the C-424 was the only one that was also built by MLW - and indeed, the first MLW unit (CP 8300) was delivered in April 1963, one month before the first ALCO-built units (EL 2401-2415).


The C-420 was an intermediate-horsepower model using a 12-cylinder 251 engine rated at 2,000 horsepower, jointly replacing the RS-32 and RS-36. While the engine and long hood were several feet shorter than on the C-424, the underframe on the C-420 was 11" longer (60' 3" over the coupler pulling faces), and the truck centers were 23" longer (34' 5"). This left room for a much longer short hood which (when full-height) could house a steam generator, with water tanks in the extra space between the trucks. As most units were built for freight service, they benefited from a larger fuel tank.

Owing to the smaller engine, the radiators at the rear did not extend beyond the sides of the hood as on other Century models. While most were built with Type B trucks, the last few LIRR C-420's featured ALCO's new high-adhesion truck design, with the bolster supported by two stacks of springs on the outside middle of the truck frame, and primary springs directly above the axles.

All but 2 of the 131 C-420's produced were for US roads, where the biggest users were LIRR, LN, Monon and SAL.


The C-424's position as a middle-man between the EMD GP30 (2,250 hp) and the GE U25B (2,500 hp) was short-lived. In late 1963, after less than 2 years of GP30 production, EMD introduced the 2,500 horsepower GP35. At the request of EL (which had been the first customer for the C-424), ALCO developed the C-425 in late 1964, which used an uprated generator to reach 2,500 hp. Two hood doors immediately behind the cab, which had been present in early C-424 production but later removed, were re-added, and the three doors under the front air intakes were made taller. A slightly larger radiator fan was adopted from the C-628 introduced a few months earlier, resulting in a raised panel extending out from the hood slightly under the radiators.

After its introduction, the C-425 was built concurrently with the C-424, with a total of 91 produced for US railroads.



Three phases for the C-424 were described in Railroad Model Craftsman, July 1985, based on the battery box location, rear numberboards, and engine air intakes. I've further divided them into several sub-phases based on other minor details.

Phase 1a 1b 2a 2b 3a 3b 3c
Dates (ALCO) 1963-04 -
1963-09 -
1964-03 -
1964-06 -
[none] 1965-04 1965-09 -
Dates (MLW) 1963-04 [none] 1964-12 1965-03 -
1965-12 -
1966-05 -
Intakes above
center hood doors
Louvers in
first section
No louvers
Rear numberboards Extend beyond carbody Notched into carbody
Radiators Near hood end Moved forward approx. 6.5"
Hood section
under exhaust stack
(1)Single vertical opening behind narrow door;
seam ahead of radiators moved forward 12";
4 shorter hood doors underneath
2 tall + 2 short hood doors
Hood behind cab Grabirons on left side;
2 doors above battery boxes
No grabirons or doors above battery boxes
Air reservoir supports Attached to straight connector
with a notch in side sill
Bolted on top of side sill
Battery boxes Fore and aft of the cab Under left rear walkway
Handrail stanchions Attached to top of walkway;
oblong openings in side sill underneath
Attached to side sill;
angled brace on battery boxes;
no oblong openings
Air reservoirs One on each side;
cooling manifold behind each reservoir
Both on right side;
cooling manifold on left side
Hood door handles Curved Straight, nearly flush with hood (except MLW units)
Underframe   Revised sand and air pipes
behind corner steps
Front air intake Small square grid, fastened with tabs Wire mesh on top of large square grid,
fastened with rectangular frame
Phase 1a 1b 2a 2b 3a 3b 3c


  1. Hood section under exhaust stack, Phase 1: Two horizontal openings on hinged raised rectangular panel; 2 + 4 hood doors underneath (2 + 3 doors on initial ALCO drawings; used on CP 8300 only)


The only previous phases I've come across for the C-420 were created by Tiger Valley models, and described two sets of details: The frame phase and the hood phase. I've elected to create new phases that are more in line with those commonly used for the C-424. Some shared detail changes (such as handrail stanchion type) were not adopted on all models at the same time.

Phase 1a 1b 2a 2b 2c
Dates 1963-06 -
1964-06 -
1964-12 1965-05 -
1965-12 -
Air reservoir supports 1 Attached to straight connector
with a notch in side sill
Bolted on top of side sill
Hood door behind front
air intake (left side) 2
3/4 height Full height (same as engine room doors);
Hinged roof panel extended forward
Hood section
under exhaust stack 3
2 small vertical intakes on bolted panel;
4 tall hood doors
Single vertical opening behind narrow door;
4 shorter hood doors
2 tall + 2 short hood doors
Hood door handles 4 Curved Straight, nearly flush with hood
Front air intake 5 Small square grid, fastened with tabs Wire mesh on top of large square grid,
fastened with rectangular frame
Small front hood intakes 6 Flush louvers Grills with outer frame
Handrail stanchions 7 Attached to top of walkway;
oblong openings in side sill underneath
Attached to side sill;
angled brace on battery boxes;
no oblong openings
Phase 1a 1b 2a 2b 2c

These drawings illustrate Phase 1a and Phase 2c C-420's built to LHR specs. The Phase 1a version has the small flat fuel tank while the Phase 2c version has the largest fuel tank with a rounded extension along most of its length. Neither is equipped with dynamic brakes.

Phase 1a -  Phase 2c


The two main phases of the C-425 were described in Railroad Model Craftsman, September 1995; I've divided Phase 2 into three subphases based on additional details.

When the C-425 was introduced, it adopted the side sill-mounted handrail stanchions and air reservoir supports that had appeared on the C-628 a few months earlier. The C-424 (and later the C-420) adopted these features soon afterward. Phases 2a through 2c for the C-425 were concurrent with phases 3a through 3c for the C-424.

Phase 1 2a 2b 2c
Dates 1964-10 -
1964-12 -
1965-06 -
1965-12 -
Battery boxes 1 Fore and aft of the cab Under left rear walkway
Air reservoirs 2 One on each side;
cooling coil behind each reservoir
Both on right side;
cooling coil on left side
Hood door handles 3 Curved Straight, nearly flush with hood
Underframe 4   Revised sand and air pipes
behind corner steps
Front air intake 5 Small square grid, fastened with tabs Wire mesh on top of large square grid,
fastened with rectangular frame
Small front hood intakes 6 Flush louvers Grills with outer frame
Raised panel under radiators 7 Notched bottom corners Straight bottom corners
Hood under radiators 8 Small square vent
on left side
Right side radiator
intake slightly shorter
Small square
vent covered
Hood doors
below exhaust stack 9
4 short 2 short, 2 tall
Phase 1 2a 2b 2c

These drawings illustrate Phase 1 and Phase 2c C-425's built to PRR specs. Railroad-specific details include the horizontal headlight with the horn mounted above, the dummy MU receptacles on the end handrails, and the high-clearance corner steps (with closer step spacing and the bottom step about 3.5" higher than standard).

The Phase 2c version also has a 2-cylinder handbrake chain, which a few railroads specified, along with a slightly higher-capacity fuel tank (rounded along most of its length rather than just the middle section).

Left side: Phase 1 -  Phase 2c

Right side: Phase 1 -  Phase 2c

Railroad Variations


CP C-424's were built by MLW in Canada. As the first C-424 built, CP 8300 (later renumbered 4200) had Phase 1a spotting features and was the only CP unit originally equipped with rear numberboards and classification lights. It also had unique Farr (or similar) radiator intakes with vertical slots. Later CP units had Phase 3a or 3b features.

All were built with dynamic brakes, larger Pyle headlight housings (double in the front, single in the rear), and Nathan M3H horns. As they were (initially) intended strictly as road units rather than road switchers, they were built with a rock deflector pilot at the front and an open pilot at the rear with no footboards or lower end plate.

Most remained in service on CP for more than 30 years, during which time they received many modifications:

Additionally, several CP C-424's received alternators from retired M-630 units late in their service careers. These units were CP 4202-4206, 4210-4211, 4213-4215, 4220, 4223, 4228, 4234 and 4244 (possibly others in the mid-1990s). Externally, this modification resulted in the addition of a third air reservoir under the left walkway (for air start) and an additional curved housing above the central air intake. The piping normally located under the left walkway was shortened to make room for the air reservoir. The exact location of the shortened piping and air reservoir straps varied between units.

NdeM / NW / WAB

At the time the C-424 and C-425 were built, NW typically ordered locomotives with a high short hood. However, most C-424 and C-425 units they ended up operating had low short hoods as they were initially ordered by either Ferrocarriles Nacionales de México (NdeM) or Wabash (WAB).

The first of what would later be NW C-424's came from what was initially an order for 30 units by NdeM, to be numbered 8100-8129. For financing reasons, the first seven units (to be 8100-8106) were diverted to Wabash in March 1964. As the cab instructions were in Spanish, they were restricted to trailing-only status and numbered WAB B900-B906. One unit (B902) was wrecked before the merger of the Wabash and NW in late 1964; the remainder were renumbered NW 3900-3901 and 3903-3906 (later NW 421-425) and modified to be able to lead. Built to NdeM specs, they were generic in appearance, with a flat fuel tank, dynamic brakes, and Phase 2a spotting features. The only notable exterior features were an unusual Nathan P2 horn (with bells #1 and #2 on the standard 5-bell manifold) and an equipment box attached to the fuel tank on the engineer's side. Wabash removed the footboards; NW later re-added them as well as adding all-weather windows to the cab sides.

In June 1964, NdeM took delivery of the remaining 23 units of the original order (numbered 8107-8129) and the first seven units (8100-8106) were replaced as a new order. They were identical in appearance to the Wabash units prior to modifications. NdeM would later take delivery of another 15 units numbered 8130-8144, with similar specifications but Phase 3c features. Many NdeM units had the horn relocated from the top of the cab roof to one of several locations in front of the cab.

In 1964, Wabash also made an order of their own for seven C-425 units to be numbered 582-589. As the merger with NW occurred prior to completion of the order, they were delivered in October 1964 as NW 1000-1006, but retained Wabash specifications such as a low short hood, no dynamic brakes, a larger rounded fuel tank (still with the filler and gauge at the rear), and wind visors and metal awnings on the cab sides. They were among the first C-425's built and had Phase 1 features.

A final 10 C-425's would be delivered as NW 1007-1016 in January 1965, built to NW specs with a high short hood (set to operate long hood forward), dynamic brakes, a rounded fuel tank with the filler and gauge slotted in the middle, Leslie S-5T horns, fabric cab awnings (later replaced by all-weather windows), and Phase 2a features. NW 1011:1 was wrecked only a few months after entering service; parts were shipped to ALCO and used in the construction of a replacement unit numbered 1011:2, built in December 1965 with Phase 2c features.


In May 2013, I made a trip to Exporail and took ground-level measurements of many of the locomotives there. The first drawings to benefit from these measurements were MLW C-424 variations.


MLW C-424 - conductor's side
MLW C-424 - engineer's side

Sample Photos

The photos below show CP C-424 #4237 and control cab #1100 (formerly C-424 # 4236). Both were originally built in December 1965 as Phase 3b units, and were later significantly modified by CP (listed above in "Railroad Variations"). However, neither was among the CP units retrofitted with an M-630 alternator.

left front photo
left front middle photo
left rear middle photo
left rear photo

Detail photos showing the conductor's side of CP #1100
right front photo
right front middle photo
right rear middle photo
right rear photo

Detail photos showing the engineer's side of CP #4237
dynamic brakes

Dynamic brakes were contained in a raised housing along the middle of the roof and supplied by two extra air intakes above the center-most hood doors (the third rear-most intake remained on units without dynamic brakes).

Due to the staggered power assemblies on the engine block, the roof panels were not mirrored on either side but rather were a 180-degree flip. In both cases, the left-most panel was slightly wider and the rest were offset to the right.


ALCO Products Inc. (1963). ALCO Century 420, DL-721A. [Specifications].

ALCO Products Inc. (1963). ALCO Century 424, DL-640A. [Specifications].

ALCO Products Inc. (1963). DL-640A Elevation, C-424. [Drawing].

Craig, R. (2022). Alco Century 424 Production Roster. Retrieved December 2023 from

Gibson, T. Alco Century Roster. Retrieved January 2008 from

Norfolk and Western Historical Society. Diesel List. Retrieved January 2024 from

Sarberenyi, R. Alco's C424 - Original Owners. Retrieved December 2017 from

Sarberenyi, R. Alco's C425 - Original Owners. Retrieved December 2017 from

Steinbrenner, R. T. (2011). The American Locomotive Company: A Centennial Remembrance. Warren, NJ: On Track Publishers, LLC.

van Schoonhoven, W. (2018). CP 4200 Series. Retrieved December 2023 from