The NZR A^A class consisted of ten

steam locomotive A steam locomotive is a locomotive that provides the force to move itself and other vehicles by means of the expansion of steam. It is fuelled by burning combustible material (usually coal, oil or, rarely, wood) to heat water in the locomot ...

s built by

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 ...

in 1914 to an order by Chief Mechanical Engineer, H. H. Jackson for operation on

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Introduction and design

Built to a similar but vastly improved design to the Q class of 1901, they had a wheel arrangement of

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 ...

and were suited to hauling freight services in the North Island (Originally they were to be classed Q^B but as they were to supplement the A class, given their aforementioned designation.) The United States built locomotives were an urgent order needed due to heavy demand with both New Zealand and British workshops unable to supply as the

First World War World War I (28 July 1914 11 November 1918), often abbreviated as WWI, was one of the deadliest global conflicts in history. Belligerents included much of Europe, the Russian Empire, the United States, and the Ottoman Empire, with fightin ...

was draining resources and manpower for the war effort. Construction was completed less than two months after the order was placed and all ten entered service in New Zealand in June 1915. Bar frames were used by the American builders instead of NZR's preferred plate frames, and the class had superheaters as built. Water capacity was double that of the A class and coal a quarter more.

Service

They were worked hard for four decades before being supplanted by the more powerful "K" and "J" class families. In 1919 No. 654 was used for a very short experiment in the use of pulverized coal. Only one trip is known to have been made before the engine was converted back. They were initially equipped with grates smaller than either the A or A^B class. Not an issue with hard coal, increasing use of soft

Waikato Waikato () is a Regions of New Zealand, local government region of the upper North Island of New Zealand. It covers the Waikato District, Waipa District, Matamata-Piako District, South Waikato District and Hamilton, New Zealand, Hamilton City ...

coal meant a larger grate was desirable. Thus the entire class had their boilers replaced with A^B class types starting in 1940 giving the reliable locomotives more life. This soon became a blessing when they were worked hard through the

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. They were used extensively on the steeply graded central

North Island Main Trunk The North Island Main Trunk (NIMT) is the main railway line in the North Island of New Zealand, connecting the capital city Wellington with the country's largest city, Auckland. The line is long, built to the New Zealand rail gauge of and ser ...

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and Gisborne sections. In the mid-1950s most of the class were still in reasonable condition and the engines were regarded as a very successful class, capable of taking somewhat heavier loads than an A^B class. The first withdrawals occurred in December 1955, when six were taken out of service with their boilers returned to the A^B class boiler repair pool. The remaining four continued to operate until February 1957. None were preserved.

References

Citations

Bibliography

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External links

Baldwin Steam Trust - New Zealand locomotives built by Baldwin, including A^A class statistics

Plan of an A^A class locomotive by Derek Brown

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