Steam locomotive
United States

Locomotives for American railroads were nearly always built in the United States with very few imports, except in the earliest days of steam engines. This was due to the basic differences of markets in the United States which initially had many small markets located large distances apart, in contrast to Europe's higher density of markets. Locomotives that were cheap and rugged and could go large distances over cheaply built and maintained tracks were required. Once the manufacture of engines was established on a wide scale there was very little advantage to buying an engine from overseas that would have to be customised to fit the local requirements and track conditions. Improvements in engine design of both European and US origin were incorporated by manufacturers when they could be justified in a generally very conservative and slow-changing market. With the notable exception of the USRA standard locomotives built during World War I, in the United States, steam locomotive manufacture was always semi-customised. Railroads ordered locomotives tailored to their specific requirements, though some basic design features were always present. Railroads developed some specific characteristics; for example, the Pennsylvania Railroad and the Great Northern Railway had a preference for the Belpaire firebox. In the United States, large-scale manufacturers constructed locomotives for nearly all rail companies, although nearly all major railroads had shops capable of heavy repairs and some railroads (for example, the Norfolk and Western Railway and the Pennsylvania Railroad, which had two erecting shops) constructed locomotives entirely in their own shops. Companies manufacturing locomotives in the US included Baldwin Locomotive Works, American Locomotive Company (ALCO), and Lima Locomotive Works. Altogether, between 1830 and 1950, over 160,000 steam locomotives were built in the United States, with Baldwin accounting for the largest share, nearly 70,000.

Steam locomotives required regular and, compared to a diesel-electric engine, frequent service and overhaul (often at government-regulated intervals in Europe and the US). Alterations and upgrades regularly occurred during overhauls. New appliances were added, unsatisfactory features removed, cylinders improved or replaced. Almost any part of the locomotive, including boilers, was replaced or upgraded. When service or upgrades got too expensive the locomotive was traded off or retired. On the Baltimore and Ohio Railroad two 2-10-2 locomotives were dismantled; the boilers were placed onto two new Class T 4-8-2 locomotives and the residual wheel machinery made into a pair of Class U 0-10-0 switchers with new boilers. Union Pacific 's fleet of 3-cylinder 4-10-2 engines were converted into two-cylinder engines in 1942, because of high maintenance problems.
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