Southern Pacific Company's MC-6 class of steam locomotive

Steam locomotive

A steam locomotive is a railway locomotive that produces its power through a steam engine. These locomotives are fueled by burning some combustible material, usually coal, wood or oil, to produce steam in a boiler, which drives the steam engine...

s is made up of two batches: the first consisting of 15 locomotives weighing 435800 pounds (197.7 t) built in 1912, the second consisting of 5 locomotives weighing 437100 pounds (198.3 t) built in 1913. All of the locomotives were built by Baldwin Locomotive Works

Baldwin Locomotive Works

The Baldwin Locomotive Works was an American builder of railroad locomotives. It was located in Philadelphia, Pennsylvania, originally, and later in nearby Eddystone, Pennsylvania. Although the company was very successful as a producer of steam locomotives, its transition to the production of...

. This was the last class of 2-8-8-2

2-8-8-2

.A 2-8-8-2, in the Whyte notation for describing steam locomotive wheel arrangements, is an articulated locomotive with a two-wheel leading truck, two sets of eight driving wheels, and a two-wheel trailing truck. The equivalent UIC classification is, refined to Mallet locomotives, D1...

 locomotives that Southern Pacific (SP) ordered as cab forward

Cab forward

The term cab forward refers to various rail and road vehicle designs which place the driver's compartment substantially farther towards the front than is common practice.- Rail locomotives :...

 locomotives.

Locomotive number 4043, the newest of the early class of MC-6 locomotives, was displayed at the Panama-Pacific International Exposition

Panama-Pacific International Exposition (1915)

The Panama-Pacific International Exposition was a world's fair held in San Francisco, California between February 20 and December 4 in 1915. Its ostensible purpose was to celebrate the completion of the Panama Canal, but it was widely seen in the city as an opportunity to showcase its recovery...

 along with SP's first locomotive, C. P. Huntington

C. P. Huntington

C. P. Huntington is a 4-2-4T steam locomotive currently on static display at the California State Railroad Museum in Sacramento, California, USA. It is the first locomotive purchased by the Southern Pacific Railroad, carrying that railroad's number 1. The locomotive is named in honor of Collis P...

.

All but three of the locomotives in this class were rebuilt as class AC-3

Southern Pacific class AC-3

Southern Pacific Railroad's AC-3 class of steam locomotive was the last cab forward design based on the 2-8-8-2 wheel arrangement. All 20 locomotives in this class were rebuilds from MC-6 class locomotives originally built by Baldwin Locomotive Works in 1912 and 1913...

 with "simpled" uniform cylinders of 22 by 30 in (558.8 by 762 mm) by 1930. The last three were thus rebuilt in 1937. During the rebuild, 4¼-BL Worthington feedwater heater

Feedwater heater

A feedwater heater is a power plant component used to pre-heat water delivered to a steam generating boiler. Preheating the feedwater reduces the irreversibilities involved in steam generation and therefore improves the thermodynamic efficiency of the system...

s were also installed on the fireman's side of the locomotives.

After their rebuilds, the locomotives were used through the end of World War II with the last one scrapped on August 20, 1949