The NZR UD class was a class of two 4-6-0

4-6-0

Under the Whyte notation for the classification of steam locomotives, 4-6-0 represents the wheel arrangement of four leading wheels on two axles in a leading truck, six powered and coupled driving wheels on three axles, and no trailing wheels. This wheel arrangement became the second-most popular...

 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...

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built by the 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...

 in 1904 for the Wellington and Manawatu Railway Company. Two locomotives were built.

Specification

Weighing 39.5 tons with a tender of 27.4 tons, they could haul express trains easily at 50 miles per hour (22 m/s) in suitable parts of the country.
With huge (for the period) 58 inches (147 cm) coupled driving wheels, a working steam pressure of 185 pound per square inches (1,275,530 Pa), and 16.5 inches (42 cm) diameter cylinders with 22 inches (56 cm) piston strokes, the handsome "Ud"s were more than capable of making up lost time with mile-a-minute runs as recalled with pride by old Manawatu railway employees.

Withdrawal

However, fast and powerful as they were the "Ud"s were unable to survive the standardisation program between 1925 and 1935 and were written off in 1929.