ALCO HH series

ALCO HH series
Portland Terminal Company HH600 #1004, photographed at Portland, Maine in 1968.
Type and origin Power type Diesel-electric Builder ALCO Total produced HH600: 79 HH660: 43 HH900: 21 HH1000: 34
Specifications 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 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)

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 was produced; comprising one prototype and four production models of varying power outputs.