Alco Century Series Diesels: Models, Production Totals & History

Last revised: August 26, 2026

Alco introduced the Century line in Chicago on January 29, 1963, as a clean-sheet road-switcher family meant to replace the RS and RSD series and to fight Electro-Motive and a newly independent General Electric. Production at Schenectady ran from June 1963 (the first C420s) through November 1968 (the last C636s). Alco-built Century catalog models total 665 units. Montreal Locomotive Works and A.E. Goodwin added more of the same designs, and MLW then launched the related M-line after Alco left the locomotive business.

Pennsylvania Railroad Alco C628 6302 at Altoona Pennsylvania June 1965 Fred Byerly

Pennsylvania Railroad C628 #6302 at Altoona, Pennsylvania, June 1965. Fred Byerly photo. American-Rails.com collection.

On this page: At a glance · Why the Century existed · Naming · Model directory · Production table · MLW and Goodwin · Schenectady closes · What still runs

At a Glance

Item	Detail
Builder	American Locomotive Company, Schenectady, N.Y. (engines from Auburn, N.Y., for most of the run)
Line	Century series (C415 through C636, plus C855 and C643DH specials)
Launch	January 29, 1963, Chicago
Alco production	June 1963 – November 1968 (two T-6 switchers in January 1969 were not Centuries)
Prime mover family	Alco 251 (12- and 16-cylinder road units; C415 used a smaller 251)
Alco-built Century catalog	665 (C415, C420, C424 Alco, C425, C430, C628, C630 Alco, C636 Alco, C855/C855B). Add 3 C643DH if you count the hydraulics.
First catalog trio	C420, C424, and a C624 that was dropped for the C628 before any C624 was built
Best-selling six-axle	C628 (186)
Best-selling four-axle (Alco only)	C420 (131); C424 reaches 190 only with 92 MLW units
Rarest road models	C430 (16), C636 (34 Alco), C415 (26), C855 (3), C643DH (3)
Successor family	MLW M-line (M420, M630, M636, M640) after 1969

Why the Century Existed

Alco was not a diesel novice in 1963. The company had pioneered the road-switcher with the RS1 in 1941, sold S-series switchers by the thousand, and held a clear second place behind Electro-Motive through the 1940s and much of the 1950s with FAs, PAs, and the RS/RSD lines. What it had not done was keep pace with EMD’s GP/SD catalog or with the electrical manufacturer that had once been its partner.

General Electric supplied generators and traction motors for Alco diesels for decades. In 1959–61 GE brought out its own Universal road locomotives, the U25B first among them, and moved into second place. Alco dropped to third. The 244-series engine of the late 1940s and 1950s had already spent goodwill with mechanical departments. The 251 was the better engine; the Century carbody and a new model-number system were supposed to make that obvious.

John Kirkland notes in The Diesel Builders, Volume Two that 251 production itself had already shifted. Twelve-cylinder 251s left Schenectady in 1961; sixteen-cylinder engines moved to Auburn, New York, the following year. Engine serials change from five digits (Schenectady) to four (Auburn). That changeover sits under the last RS11, RS36, RSD12, RS32, RS27, and early C424 orders. Century carbodies were still erected at Schenectady.

How the Names Work

Alco dropped the RS/PA letter codes for a three-part Century number:

C = Century
First digit = axles in the truck count that mattered for the model (4 = B-B, 6 = C-C, 8 on the C855 for its B-B+B-B arrangement)
Last two digits = the first two figures of the horsepower rating (C420 = 2,000 hp, C628 = 2,750 hp rounded in the code, C636 = 3,600 hp)

Specification numbers stayed in the old DL series underneath: DL721A for the C420, DL640A for the C424, DL628 for the C628, DL636 for the C636, and so on. Spotters still use both.

The Models

Four-axle Centuries were the volume road-switchers. Six-axle Centuries were the drag engines. The C415 is a center-cab switcher wearing a Century number. The C855 and C643DH are one-off experiments for Union Pacific and Southern Pacific.

Four-axle road units

C420 (DL721A), 2,000 hp, 12-251C, 131 built, 1963–68. The first Century in production. Long Island took 30, including steam-generator passenger units and a late Hi-Ad batch. Other buyers included Seaboard Air Line (27), Monon, Louisville & Nashville, Lehigh Valley, and Lehigh & Hudson River. This is the Century you still see in short-line freight.

C424 (DL640A), 2,400 hp, 16-251B, 98 Alco + 92 MLW = 190, 1963–67. Cheaper stablemate of the C425. Alco’s own 98 included a large Nacionales de México order (45). MLW built 41 for Canadian National and 51 for Canadian Pacific. All rode AAR Type B trucks.

C425 (DL640B), 2,500 hp, 16-251C, 91 built, 1964–66. Alco’s answer to EMD’s GP35 and GE’s U25B. U.S. buyers only. A slightly larger radiator fan, inherited from the C628, is the spotting tell versus a C424.

C430 (DL430 2nd), 3,000 hp, 16-251E, 16 built, 1966–68. Last four-axle Century freight diesel. Reading 2, New York Central 10 (first with Hi-Ad trucks), Green Bay & Western 1, plus three demonstrators that became Seaboard Coast Line 1275–1277. GB&W #315 (February 1968) was the last C430.

Six-axle road units

Alco cataloged a C624 with the C420 and C424, then dropped it for more horsepower before any were built. The production six-axle line is C628–C630–C636.

C628 (DL628), 2,750 hp, 16-251C, 186 built, 1963–68. Alco’s best-selling six-axle Century and the replacement for the RSD-15. Atlantic Coast Line took the first production units in December 1963. Pennsylvania, Norfolk & Western, Delaware & Hudson, Southern Pacific (including the four demonstrators), and several Mexican and Australian buyers followed. Early units rode Trimounts; the carbody is the six-axle Century look everyone knows.

C630 (DL630), 3,000 hp, 16-251E, 77 Alco + 56 MLW = 133, 1965–69. Direct shot at EMD’s SD40 and GE’s U30C. Alco buyers: ACL, C&O, L&N, N&W, Pennsylvania, Reading. MLW continued the model for CN, CP, and Pacific Great Eastern after Schenectady stopped. Two stacked grilles on the intercooler box distinguish a C630 from a C636 (upper grille only).

C636 (DL636), 3,600 hp, 16-251F, 34 Alco (plus 35 Goodwin C636s), 1967–68. Most powerful single-engine Alco diesel. Aimed at the SD45. U.S. railroad buyers were only SP&S (10), Penn Central (15, a PRR order), and Illinois Central (6), plus three demonstrators. Delaware-Lackawanna #3642 is the last unrebuilt Alco C636 in service.

Pair of Atlantic Coast Line Alco C628s leaving Rocky Mount North Carolina with extra 2008 Warren Calloway

A pair of Atlantic Coast Line C628s leave Rocky Mount, North Carolina, with extra 2008 in the 1960s. Warren Calloway photo.

Switcher and specials

C415 (DL415), 1,500 hp, 1966–68, 26 built. Center-cab switcher with optional cab heights, not a road-switcher. Rock Island took ten, Southern Pacific ten, plus Chehalis Western, Columbia & Cowlitz, Monongahela Connecting, SP&S, and the demonstrator (later Hamersley Iron 008). Last C415s came out in December 1968, the same month as the last C636s.

C855 / C855B (DL-855 / DL-856A), 5,500 hp, 1964, 3 units for Union Pacific. Two 16-251C engines on one frame, B-B+B-B trucks, about 551,000 pounds. UP 60, 61, and booster 60B. Built to cut the number of units per train. They did not last.

C643DH (DH643), 4,300 hp hydraulic, 1964, 3 units for Southern Pacific. Twin 12-251C engines and Voith hydraulic transmission, not electric drive. SP 9018–9020. Alco’s diesel-hydraulic experiment; all were gone from SP by the early 1970s. A proposed C650DH was never built.

Production Table

Alco Schenectady figures below follow Extra 2200 South / Kirkland-style counts used on the individual model pages, aligned with the year-by-year Schenectady table that sums to 665 (C643DH counted separately). MLW and Goodwin are in their own columns so a C424 or C630 “family” total is not mistaken for Schenectady output.

Model	Spec	Hp	Engine	Alco	MLW / other	Dates (Alco)	Notes
C415	DL415	1,500	251 (switcher)	26	—	1966–68	Center cab
C420	DL721A	2,000	12-251C	131	—	1963–68	First Century in production
C424	DL640A	2,400	16-251B	98	92 MLW	1963–67	Family total 190
C425	DL640B	2,500	16-251C	91	—	1964–66	U.S. only
C430	DL430 (2nd)	3,000	16-251E	16	—	1966–68	Last four-axle Century
C628	DL628	2,750	16-251C	186	—	1963–68	Best-selling six-axle Century
C630	DL630	3,000	16-251E	77	56 MLW	1965–67 (MLW into 1969)	Family total 133
C636	DL636	3,600	16-251F	34	35 Goodwin C636s (not M636)	1967–68	Not 83. M636 is a different model (111 at Montreal)
C643DH	DH643	4,300	Two 12-251C	3	—	1964	SP hydraulic; not in the 665 electric-catalog sum
C855 / C855B	DL-855 / 856A	5,500	Two 16-251C	3	—	1964	UP 60, 61, 60B

MLW, Goodwin, and the M-Line

Montreal had been Alco’s Canadian plant. After Studebaker-Worthington took MLW, and after Schenectady quit locomotives, MLW kept selling Century-derived six-axles as the M630 and M636, then the four-axle M420 and the one-off 4,000 hp M640. Those locomotives ride Dofasco trucks, not Alco Hi-Ads, and they are not C636s. Montreal built 111 M636s (CP 44, CN 40, Cartier 11, Ferrocarril del Pacífico 16). A.E. Goodwin in Australia built C628s and C636s under license, then M636 copies; Comeng finished the last Australian M636 in 1980.

If a roster says “C636” and the builder is MLW, it is probably an M636. Genesee Valley Transportation’s Delaware-Lackawanna fleet is the living example: one Alco C636 (#3642) among several MLW M630s and M636s.

The End at Schenectady

The C636 was Alco’s last high-horsepower Century. It was not the last Alco locomotive. November 1968 saw SP&S C636s 340–343, the three C636 demonstrators, and late C415s. The plant’s last units were Newburgh & South Shore T-6 switchers #1016 and #1017, released January 8 and 10, 1969. Alco dated the locomotive exit December 31, 1968, with those two T-6s as the short overrun. A canceled Pakistan order and a canceled Penn Central C430 follow-on (15 units) sat on the books as the shop emptied. U.S. diesel deliveries in 1968 had fallen below 1,000 in a market that had once seen 4,500 in a year.

Delaware & Hudson C628 and U33Cs at Afton, NY in 1970 Marty Bernard

Delaware & Hudson C628 #609 and a pair of former Erie Lackawanna U33Cs (including #701) - part of the swap with EL for the three SD45s - are in freight service at Afton, New York on August 14, 1970. Marty Bernard photo.

What Still Runs

Four-axle Centuries outlived the Class Is that bought them.

Arkansas & Missouri still owns a large C420 fleet (ex-SAL, LV, L&HR). SD70ACes now lead most road trains; some C420s remain in the assignment. Photos from 2025 still show them on property and on extras.
Livonia, Avon & Lakeville remains an Alco short line (C420/C425 territory).
Delaware-Lackawanna (GVT) runs C420s, C425s, and the unique C636 #3642 out of Scranton, plus MLW six-motors on the Pocono grades.
Adirondack Railroad took three ex-NYC C430s from Western New York & Pennsylvania in 2025.
Apache Railway was the desert Century showplace (C420/C424) until the Snowflake mill crisis of 2012. The railroad survived; do not assume the Alco fleet is still the daily power without a current check.

Six-axle Centuries are almost gone in unrebuilt Alco form. Surviving C628s are overseas. The C630’s afterlife is mostly MLW and rebuilds. The C636’s afterlife is one locomotive in Pennsylvania and a larger family of M636s.

Sources

Kirkland, John F. The Diesel Builders, Volume Two: American Locomotive Company and Montreal Locomotive Works. Glendale: Interurban Press, 1989.
Solomon, Brian. Alco Locomotives. Minneapolis: Voyageur Press, 2009.
Diesel Era / Withers, Alco’s Century Series, Volumes 1 and 2 (four-axle and six-axle).
The Diesel Shop, Alco Century and MLW M630/M636 production rosters (Extra 2200 South tradition).
Individual American-Rails model pages for C415, C420, C424, C430, C628, C630, C636, C855 (serial blocks and owner totals).

Alco column totals are the Schenectady catalog. Family totals that include MLW or Goodwin are labeled as such.

Facebook X Pinterest Tumblr Reddit WhatsApp Messenger