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The NZR KA class of 1939 was a class of mixed traffic 4-8-4 steam locomotives that operated on New Zealand's railway network. They were built after the success of the K class to meet the increasing traffic demands of the New Zealand Railways Department. The locomotives first appeared with distinctive streamlining, mainly to hide their ACFI feedwater heater systems.
History
Following the success of the K class, there was a need for more similar locomotives in the North Island. The new locomotives incorporated a number of improvements, including a re-designed plate frame to eliminate the cracking issues the K class were experiencing; roller bearings on all wheels; hydrostatic lubrication throughout; and the inclusion of the ACFI feedwater heater system as pioneered by K 919. As the ACFI equipment was criticised for its aesthetic appearance, it was obscured with shrouding fitted to both the KA class and contemporary KB class.
Building of the locomotives commenced in 1939, just prior to the Second World War. Main construction and assembly took place at Hutt Workshops. Hillside Workshops largely constructed - but did not assemble - ten of the class (No.'s 940-944, 960-964) and built a further five KA boilers. The primary reason why the ten KAs were not assembled at Hillside was that there was no way of transporting complete locomotives between the North and South Islands at the time (the first inter-island rail ferry did not commence until 1962). Vulcan Foundry of the United Kingdom supplied parts for fifteen locomotives, including most chassis components, tender bogies, and boiler foundation rings. The General Casting Corporation of Pennsylvania, United States supplied trailing bogie and rear end framing. A company in Auckland also constructed up to 10 tenders for the class. While the imported components were intended for specific locomotives (and in some cases were stamped for the locomotives they were intended for) in practice, and due to wartime pressures, the imported components were used indiscriminately for any KA locomotives in the programme.
Nineteen locomotives were built between 1939 and 1941, but wartime circumstances meant construction of the remaining sixteen lasted from 1941 to 1950, a period much longer than NZR management anticipated. The first of the locomotives to be completed was KA 945. All but two members of the class were constructed by 1946. The final pair, numbers 958 and 959, differed somewhat from the rest of their class due to being fitted with Baker valve gear instead of the Walschaerts valve gear fitted to all other members, and were oil burners from new. Like some of the other later KAs, they were not built with shrouding, although the front shrouding and many front-end components had been built for KA 959 for display at an exhibition. These were ultimately used on KA 939.
In service
The KA class was solely based in the North Island, and upon entering service, the first members were placed on heavy freight and express passenger service. They saw extensive use on these tasks during wartime. The shrouding, while cleaning up the appearance of the locomotives, was open at the top and began gathering soot and dust that affected the working environment in the cab. After the war, a coal shortage also occurred and NZR decided to convert a large number of locomotives to oil burning. The KA class were a prime candidate due to the large size of the grate. Conversion to oil-burning occurred from 1947 and 1953, with nineteen of the class done at Otahuhu Workshops and sixteen at Hutt. The conversion coincided with the removal of the shrouding, and also the replacement of the ACFI feedwater system with an exhaust steam injector. Due to coal shortages, the locomotives were eventually all converted to oil firing between 1947 and 1950. As a result, the locomotives were able to obtain faster speeds, with speeds up to recorded.
The locomotives became a mainstay of the North Island motive power fleet and were primarily seen on the North Island Main Trunk Railway, operating the overnight Express and Night Limited from 1940. When the North Island JA entered service in 1952 they took over the Express and Limited on the Taumaranui - Auckland section, but the KA continued to be used on the Paekakariki - Taumaranui section of the Limited and Express, until displaced by DA class diesel locomotives between 1963 and 1965. On the last day of the steam power on the Limited, in April 1963 and the Express in February 1965, KA locomotives, worked the train right through to Auckland.