Maine Central Railroad Class O locomotives were originally intended for heavy freight service. They were of

4-6-0 A 4-6-0 steam locomotive, under the Whyte notation for the classification of steam locomotives by wheel arrangement, has four leading wheels on two axles in a leading bogie and six powered and coupled driving wheels on three axles with the abse ...

wheel arrangement in the Whyte notation, or "2'C" in UIC classification. They replaced earlier class P

2-6-0 Under the Whyte notation for the classification of steam locomotives, represents the wheel arrangement of two leading wheels on one axle, usually in a leading truck, six powered and coupled driving wheels on three axles and no trailing wheels. ...

locomotives beginning in 1903. They were in turn replaced by class W

2-8-0 Under the Whyte notation for the classification of steam locomotives, represents the wheel arrangement of two leading wheels on one axle, usually in a leading truck, eight powered and coupled driving wheels on four axles, and no trailing wheels. ...

locomotives for the heaviest freight service beginning in 1910, but remained in use on branch line trains until replaced by

diesel locomotive A diesel locomotive is a type of railway locomotive in which the prime mover is a diesel engine. Several types of diesel locomotives have been developed, differing mainly in the means by which mechanical power is conveyed to the driving whee ...

s after World War II. They proved so well-suited for branch line service the design was among the last steam locomotives built for the Maine Central.

Original class O

Class O locomotives were numbered from 351 to 390 as delivered. The first were built in 1903 at the

American Locomotive Company The American Locomotive Company (often shortened to ALCO, ALCo or Alco) was an American manufacturer of locomotives, diesel generators, steel, and tanks that operated from 1901 to 1969. The company was formed by the merger of seven smaller locomo ...

(ALCO) plant at Schenectady, New York with builders numbers 27657-27659 and 29029–29030. Builders numbers 30323-30326 and 38170-38173 followed in 1905. Schenectady-built locomotives were equipped with Stephenson valve gear.

Sub-class O-1

Builders numbers 40576-40579 and 41235-41239 were assembled with Walschaerts valve gear in ALCO's Rhode Island plant in 1906.

Sub-class O-2

Baldwin Locomotive Works The Baldwin Locomotive Works (BLW) was an American manufacturer of railroad locomotives from 1825 to 1951. Originally located in Philadelphia, it moved to nearby Eddystone, Pennsylvania, in the early 20th century. The company was for decades t ...

built locomotives 373 through 382 with Walschaerts valve gear and weighing more than the ALCO design. Builders numbers 32267, 32268, 32304, and 32344 were delivered in 1907; and 32395, 32428, 32566, 32575, 32644, and 32675 arrived in 1908.

Sub-class O-4

Lima Locomotive Works built locomotives 383 through 390 with Baker valve gear in 1923. Builders numbers 6482 through 6489 were about the same weight as the Baldwin engines. The earlier engines had been equipped with short tenders suitable for branch line turntables. The Lima engines had a longer tender with capacity for 15 tons of coal and of water. Older O class engines received larger tenders when larger locomotives were scrapped. Baldwin Locomotives 374 and 379 received tenders from class X

Mallet locomotives The Mallet locomotive is a type of articulated steam railway locomotive, invented by the Swiss engineer Anatole Mallet (1837–1919). The front of the locomotive articulated on a bogie. The compound steam system fed steam at boiler pressur ...

. Locomotives with larger tenders were often used as helper engines.

Replacement

When the Maine Central began purchasing diesel locomotives,

switcher A switcher, shunter, yard pilot, switch engine, yard goat, or shifter is a small railroad locomotive used for manoeuvring railroad cars inside a rail yard in a process known as ''switching'' (US) or ''shunting'' (UK). Switchers are not inten ...

s intended for branch line use were numbered in the 300 series reserved for the O class. EMD SW7s and SW9s were numbered 331 through 335; and ALCO S-2s and S-4s were numbered 301-303 and 311–317.

''Big O'' passenger locomotives

Sub-class O-3 locomotives numbered 401 through 412 are not included in the infobox totals. Although they shared the 4-6-0 wheel arrangement, the number sequence reveals a different use. These were main line passenger engines built for Maine Central during the period of United States Railroad Administration (USRA) control. USRA authorised construction of a non-standard 4-6-0, because Maine Central C class

4-6-2 Under the Whyte notation for the classification of steam locomotives, represents the wheel arrangement of four leading wheels on two axles, six powered and coupled driving wheels on three axles and two trailing wheels on one axle. The locomotiv ...

s were smaller than USRA Light Pacifics. ALCO completed builders numbers 59050 through 59057 in 1918, and 62051 through 62054 in 1920. These locomotives used steam in cylinders, through drivers to achieve tractive effort.

References

{{Maine Central Steam locomotives of the United States 4-6-0 locomotives ALCO locomotives Baldwin locomotives Lima locomotives O 4-6-0 Railway locomotives introduced in 1903 Standard gauge locomotives of the United States Scrapped locomotives