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Tom Thumb was the first Americanmarker-built steam locomotive used on a common-carrier railroad. Designed and built by Peter Cooper in 1830, it was designed to convince owners of the newly formed Baltimore and Ohio Railroad to use steam engines. It is especially remembered as a participant in an impromptu race with a horse-drawn car; the "Tom Thumb" led the race until a belt slipped off a pulley and the engine lost power. The demonstration was successful, however, and in the next year the railroad, committed to the use of steam locomotion, held trials for a working engine.

Design and construction

Tom Thumb was designed by Peter Cooper as a 4-wheel locomotive with a vertical boiler and vertically mounted cylinder that drove the wheels on one of the axles. The "design" was characterized by a host of improvisations. The boiler tubes were made from rifle barrels and a blower was mounted in the stack, driven by a belt to the powered axle. Cooper's interest in the railroad was by way of substantial real estate investment in what is now the Cantonmarker neighborhood of Baltimoremarker; success for the railroad was expected to increase the value of his holdings.

Construction was carried out in the machine shop of George W. Johnson, where then 18 year old James Millholland was apprenticed. Millholland would later become a prominent locomotive designer in his own right.

Testing was performed on the company's track between Baltimore and Ellicott Mills (now Ellicott City, Marylandmarker). Two tracks had been constructed, and the driver of a passing horse-drawn car bearing passengers challenged the locomotive to a race. The challenge accepted, the Tom Thumb was easily able to pull away from the horse until the belt slipped off the blower pulley and/or a popoff valve was broken or was active. Without the blower, the boiler did not draw adequately and the locomotive lost power, allowing the horse to pass and win the race. Nonetheless, it was realized that the locomotive offered superior performance, because the technical difficulty with the Tom Thumb was recognized. Later races all showed the locomotive defeating the horse-drawn car by substantial distances, and horse victories were extremely rare, if there were any at all.

The Tom Thumb was not intended for revenue service, and was not preserved, though Cooper and others associated with the railroad's early days left descriptions which enabled the general dimensions and appearance to be worked out. In 1892, a wooden model was constructed by Major Pangborn (who also had models made of many other early locomotives), and when a replica was constructed in 1926 for the "Fair of the Iron Horse", the builders followed Pangborn's model. The replica therefore differed considerably from the original, being somewhat larger and heavier, and considerably taller (note that the dimensions given above are those of the replica). Also, instead of the blower in the stack, a much larger blower was mounted on the platform to provide a forced draft, and the support frame of the cylinder and guides was considerably different. The replica remains at the Baltimore and Ohio Railroad Museummarker.


  1. Sagle, Lawrence, B&O Power, Alvin Staufer, 1964, p. 11
  2. Sagle, p. 11
  3. Sagle, p.12

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