Portland Terminal Company HH600 No. 1004, photographed at Portland, Maine in 1968.

(Thewellman at en.wikipedia, Public domain, via Wikimedia Commons)


ALCO rectangle block logo.


The ALCO HH series was an early set of diesel switcher locomotives built by the American Locomotive Company (ALCO) of Schenectady, New York between 1931 and 1940, when they were replaced by the S series: the 660 hp (490 kW) S-1 and 1,000 hp (750 kW) S-2. They were ALCO's first diesel switchers to enter true series production, and among the first land vehicles anywhere to use the revolutionary diesel-electric power transmission.

The "HH" name stood for "High Hood", a name ALCO came eventually to use in an official context, but originally an unofficial name. Model designations such as HH600 are only semi-official. Original ALCO designations were either descriptive or based on the internal order/design number.

A total of 177 of the HH series were produced; comprising one prototype and four production models of varying power outputs.


The New Haven's Alco 600 in 1933.

(American Locomotive Company, Public domain, via Wikimedia Commons)


ALCO 600 (New Haven No. 0900)

The first HH series locomotive, ALCO demonstrator No. 600, was mechanically almost identical to later designs, but the appearance differed. The sides of the locomotive's hood sloped outward from top to bottom, and brake equipment was exposed beneath the cab. It rode on a unique pattern of trucks. After a period of demonstration on a number of railroads, the unit was sold to the New York, New Haven and Hartford Railroad as No. 0900. This number often was used to describe the locomotive, although the classification on the builder's data card was "404-OE-200". This first unit was built in July 1931.


A 6-cylinder McIntosh & Seymour engine on a flat car.

(Hallcp, Public domain, via Wikimedia Commons)


Diesel-electric power transmission

The locomotive was equipped with a four-stroke McIntosh & Seymour 531 straight-6 diesel engine, powering a General Electric GT551A1 main generator. Four nose-suspended GE-287-D traction motors in the trucks were geared at a ratio of 4.25:1 to the wheels; the motors were cooled by electrically driven traction motor blowers.



The HH600 was nearly identical to the previous No. 0900 of the New Haven internally and mechanically, but it was clad in new bodywork, with a straight-sided hood and cab sides that came all the way to the frame. The HH600's were powered by 6-cylinder McIntosh & Seymour 531 engines of 600 hp (450 kW). They were built from July 1932 through May 1939; in all, 78 HH600s were constructed. The first-built units had sharp-edged front hood corners, but in 1934 ALCO employed industrial designer Otto Kuhler to clean up the appearance; he curved the corners and recessed the headlight, and all subsequent HH series units were of this style until another restyling in 1938 where the nose was further rounded. Late versions of this locomotive used the 6-cylinder 538 engine.


Original buyers

Railroad Quantity Road numbers Notes
American Locomotive Company (prototype) 1 600 (1st) to New Haven 0900
American Locomotive Company (demonstrators) 2 1, 600 (2nd) 1 to ATSF 2300
American Locomotive Company (demonstrators) 1 601 to Lehigh Valley Railroad 105
American Locomotive Company (demonstrators) 1 602 to Boston and Maine 1102
American Locomotive Company (demonstrators) 1 603 to Delaware, Lackawanna and Western 401
Atchison, Topeka and Santa Fe Railway 1 2301 2301 retired Feb 1, 1971 Relocated to Temple, TX
Atchison, Topeka and Santa Fe Railway 1 2302 2302 to American Grain & Cattle
Belt Railway of Chicago 2 302–303
Boston and Maine Railroad 1 1101
Central Railroad of New Jersey 4 1020–1023 1021 to Houdaille Construction Materials Co.
Chicago and Eastern Illinois Railroad 1 102
Chicago and Illinois Western Railroad 1 1
Chicago and Western Indiana Railroad 1 1
Delaware, Lackawanna and Western Railroad 7 402–408 405–406 to Erie Lackawanna as 322-323
Elgin, Joliet and Eastern Railway 1 209
Hoboken Manufacturers Railroad 1 601
Illinois Central Railroad 8 9006–9013 Scrapped 1951
New York, New Haven and Hartford Railroad 10 0911–0920
Patapsco and Back Rivers Railroad 7 54–60
Peoria and Pekin Union Railway 1 100
Portland Terminal Company [Maine] 4 1001–1004
South Buffalo Railway 6 54–59
Steelton and Highspire Railroad 1 31
Universal Atlas Cement 1 4
Total 79

Rock Island Alco HH900 730 at Kansas City, Kansas, date and photographer unknown.

Alco built just 21 HH900's for eight customers. This was Rock Island's only one, originally Alco demonstrator 101.

(Craig Garver, Public domain, https://www.flickr.com/photos/digitalrailartist/50319994528/)



The HH900 was a 900 hp (670 kW) version of the HH series using a turbocharged version of the McIntosh & Seymour 531 engine. Both turbocharged models (HH900 and HH1000) needed a greater cooling capacity, and this was reflected in the larger bodyside radiator space of both models, which distinguishes them from the lower-powered HH600 and HH660. The 21 HH900 units were produced between March 1937 and January 1939, after which they were supplanted by the McIntosh & Seymour 538T-engined HH1000. Several HH900s were built with the 538T engine.


Original buyers

Railroad Quantity Road numbers Notes
American Locomotive Company (demonstrator unit) 1 101 to CRI&P 730
Birmingham Southern Railroad 8 81–88
Elgin, Joliet and Eastern Railway 1 402
Kansas City Terminal Railway 1 50
Minnesota Transfer Railway 3 90–92
Philadelphia, Bethlehem and New England Railroad 1 207 to South Buffalo Railway 70
Reading Company 2 40–41
Warrior River Terminal Company 2 50–51
Youngstown and Northern Railroad 2 211–212
Total 21

Buffalo Creek No. 43, an HH660, is owned and operated by the WNYRHS. Shown here in 2018.

(Prrbaldwin, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons, cropped)



The HH660 started production in ALCO's lineup in October 1938; 43 examples were built until April 1940. It used a naturally aspirated version of the 6-cylinder McIntosh and Seymour 538 engine, producing 660 hp (490 kW). Externally, HH660s were indistinguishable from late HH600s.


Railroad Quantity Road numbers Notes
American Locomotive Company (plant switcher)
Atlantic Coast Line Railroad 1 1900
Boston and Maine Railroad 1 1162
Buffalo Creek Railroad 1 43 To Relco - 1966, to WNYRHS - 2000
Chicago, Milwaukee, St. Paul and Pacific Railroad (“Milwaukee Road”) 4 1600–1603 Renumbered 980–983, 980-981 to Relco, 982 in Scottsdale, AZ, 983 to III Transportation then Illinois Railway Museum.
Delaware, Lackawanna and Western Railroad 3 409–411 409–410 to Erie-Lackawanna Railway 324–325
Elgin, Joliet and Eastern Railway 3 210–212 211 to Gopher State Scrap and Metal
Erie Railroad 4 302–305 305 to Erie-Lackawanna Railway, same number
Green Bay and Western Railroad 1 101
Inland Steel 1 50
Louisville and Nashville Railroad 1 10
Maine Central Railroad 2 951–952
Minneapolis and St. Louis Railway 1 D939 To Glacier Sand & Gravel
New York, New Haven and Hartford Railroad 10 0921–0930 0924 to Penn Central 9411 in 1969
Northern Pacific Railway 3 125–127 125–126 to Walla Walla Valley Railway 770, 775; 127 renumbered 602. 770 to Relco 770 to Port of Longview 770 Longview, WA.
Southern Pacific Company 3 1001–1003
Tennessee Central Railway 1 50
Wabash Railroad 2 100, 150
Total 43

Minneapolis & St Louis Alco HH1000 D-539 at Peoria, Illinois, June 13, 1939. Photographer unknown.

(Craig Garver, Public domain, https://www.flickr.com/photos/digitalrailartist/50320899687/)



The HH1000 replaced the HH900, with the new McIntosh and Seymour 538T engine, turbocharged to produce 1000 hp (750 kW), a 100 hp (75 kW) increase from the previous model. They were produced between May 1939 and December 1940; 34 were built. M&STL D539 was the only HH1000 built with the 531T engine.


Original buyers

American Locomotive Company (demonstrator unit) 1 1000
Atchison, Topeka and Santa Fe Railway 12 2310–2321
Atlantic Coast Line Railroad 1 600
Birmingham Southern Railroad 1 89
Chicago, Milwaukee, St. Paul and Pacific Railroad (“Milwaukee Road”) 1 1671
Manufacturers Railway 3 202–203
Michigan Limestone and Chemical Company 4 103–106
Minneapolis and St. Louis Railway 1 D-539 Renumbered 92; to Chicago and North Western Railway
Missouri Pacific Railroad 1 9102
Newburgh and South Shore Railway 2 1–2
Oliver Iron Mining Company 7 900–90
Total 34


Overall length 45 ft 2.75 in 13.79 m
Overall length 45 ft 2.75 in 13.79 m
Between bolster centers: 21 ft 3 in 6.48 m
Truck wheelbase: 8 ft 0 in 2.44 m
Width over grabirons: 9 ft 10 in 3.00 m
Height above rails: 14 ft 3 in 4.34 m
Wheel diameter: 40 in 1.02 m
Fuel capacity:
Engine (HH600): McIntosh & Seymour 531
Power (HH600): 600 hp 450 kW
Engine (HH900): McIntosh & Seymour 531T (turbocharged)
Power (HH900): 900 hp 670 kW
Engine (HH660): McIntosh & Seymour 538
Power (HH660): 660 hp 500 kW
Engine (HH1000): McIntosh & Seymour 538T (turbocharged)
Power (HH1000): 1000 hp 750 kW
Main generator:
Traction motors:
Standard gearing:

Surviving units

A few HH series switchers still survive in revenue service, and more are in museums. Working HH locomotives include an HH660 at Gopher Scrap in Mankato, Minnesota, one owned by the Western New York Railway Historical Society, and one from the Delaware-Lackawanna Railroad owned by Genesee Valley Transportation Company at Scranton, Pennsylvania.

Among the preserved locomotives are an HH600, four HH660s and an HH1000. Birmingham Southern No. 82, the sole surviving HH900, is on static display at the Heart of Dixie Railroad Museum in Calera, Alabama.


Southern Pacific Alco HH660 1003, date, location and photographer unknown. Probably taken at Oakland, California, between 1940 and 1946.

(Craig Garver, Public domain, https://www.flickr.com/photos/digitalrailartist/50439348271/)



Type and origin
Power type: Diesel-electric
Builder: ALCO
Total produced HH600: 79
Total produced HH660: 43
Total produced HH900: 21
Total produced HH1000: 34
Configuration: ​• AAR B-B
Gauge: 4 ft 8+1⁄2 in (1,435 mm) standard gauge
Wheel diameter: 40 in (1,016 mm)
Length: 45 ft 2+3⁄4 in (13.79 m)
Prime mover: Alco HH600/900 - McIntosh & Seymour 531; HH660/1000 - McIntosh & Seymour 538
Engine type: Inline-6 Four stroke diesel
Aspiration HH600/660: Naturally aspirated
Aspiration HH900/1000: Turbocharged
Displacement: 9,572 cu in (156.86 L)
Cylinders: 6
Cylinder size: 12.5 in × 13 in (318 mm × 330 mm)
Performance figures
Power output: 600 hp (447 kW), 660 hp (492 kW), 900 hp (671 kW), or 1,000 hp (746 kW)