# NZR AA class

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NZR AA class No. 650 at Petone between 1915 and 1920 Type and origin Power type Steam Builder Baldwin Locomotive Works Build date 1915 Total produced 10 Specifications Configuration: ​ • Whyte 4-6-2 Gauge 3 ft 6 in (1,067 mm) Driver dia. 49 in (1.245 m) Length 34 ft 9 in (10.59 m) Adhesive weight 34 long tons 14 cwt (77,700 lb or 35.3 t) 34 long tons 14 cwt (35.3 t; 38.9 short tons) Total weight 88.5 long tons (89.9 tonnes; 99.1 short tons) Fuel type Coal Firebox: ​ • Grate area 28.3 sq ft (2.63 m2) Boiler pressure 170 psi (1.17 MPa) (as coumpound) Heating surface 1,465 sq ft (136.1 m2) Cylinders 2 Cylinder size 18 in × 24 in (457 mm × 610 mm) Performance figures Tractive effort 21,580 lbf (96.0 kN) Career Operators NZGR Numbers 648 - 657 Withdrawn 1955–1957 Disposition All scrapped

The **NZR AA class** consisted of ten [steam locomotives](/source/Steam_locomotive) built by [Baldwin Locomotive Works](/source/Baldwin_Locomotive_Works) in 1914 to an order by Chief Mechanical Engineer, H. H. Jackson for operation on [New Zealand](/source/New_Zealand)'s [national rail network](/source/Rail_transport_in_New_Zealand). They were the last steam locomotive class to be built by Baldwin works.

## Introduction and design

Built to a similar but vastly improved design to the [Q class](/source/NZR_Q_class_(1901)) of 1901, they had a wheel arrangement of [4-6-2](/source/4-6-2) and were suited to hauling freight services in the North Island (Originally they were to be classed QB 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](/source/First_World_War) 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](/source/New_Zealand_Railways_Department)'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.[1]

## 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 AB class. Not an issue with hard coal, increasing use of soft [Waikato](/source/Waikato) coal meant a larger grate was desirable.[1] Thus the entire class had their boilers replaced with AB class types starting in 1940 giving the reliable locomotives more life. This soon became a blessing when they were worked hard through the [Second World War](/source/Second_World_War). They were used extensively on the steeply graded central [North Island Main Trunk](/source/North_Island_Main_Trunk), [Wanganui](/source/Marton%E2%80%93New_Plymouth_Line) and [Gisborne](/source/Palmerston_North%E2%80%93Gisborne_Line) 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 AB class. The first withdrawals occurred in December 1955, when six were taken out of service with their boilers returned to the AB class boiler repair pool. The remaining four continued to operate until February 1957.[2] None were preserved.

## See also

- [NZR Q class (1901)](/source/NZR_Q_class_(1901))

- [NZR A/AD class (1906)](/source/NZR_A_class_(1906))

- [NZR AB class](/source/NZR_AB_class)

- [NZR G class (1928)](/source/NZR_G_class_(1928))

- [Locomotives of New Zealand](/source/Locomotives_of_New_Zealand)

## References

### Citations

1. ^ [***a***](#cite_ref-FOOTNOTEMillar2011_1-0) [***b***](#cite_ref-FOOTNOTEMillar2011_1-1) [Millar 2011](#CITEREFMillar2011).

1. **[^](#cite_ref-FOOTNOTEPalmerStewart1965103_2-0)** [Palmer & Stewart 1965](#CITEREFPalmerStewart1965), p. 103.

### Bibliography

- Lloyd, W. G. (1974). *Register of New Zealand Railways Steam Locomotives 1863-1971* (2nd ed.). [ISBN](/source/ISBN_(identifier)) [0-9582072-1-6](https://en.wikipedia.org/wiki/Special:BookSources/0-9582072-1-6).

- Millar, Sean (2011). *The NZR Steam Locomotive*. Wellington: [New Zealand Railway and Locomotive Society](/source/New_Zealand_Railway_and_Locomotive_Society). [ISBN](/source/ISBN_(identifier)) [978-0-908573-89-9](https://en.wikipedia.org/wiki/Special:BookSources/978-0-908573-89-9).

- Stewart, W. W. (1974). *When Steam was King*. Wellington: [A. H. & A. W. Reed Ltd](/source/Reed_Publishing). [ISBN](/source/ISBN_(identifier)) [978-0-589-00382-1](https://en.wikipedia.org/wiki/Special:BookSources/978-0-589-00382-1).

- Palmer, A. N.; Stewart, W. W. (1965). *Cavalcade of New Zealand Locomotives*. Wellington: [A H. & A W. Reed](/source/Reed_Publishing). [ISBN](/source/ISBN_(identifier)) [978-0-207-94500-7](https://en.wikipedia.org/wiki/Special:BookSources/978-0-207-94500-7).

## External links

- [Baldwin Steam Trust - New Zealand locomotives built by Baldwin, including AA class statistics](http://www.baldwin-steam.org.nz/loco/classes.html)

- [Plan of an AA class locomotive by Derek Brown](http://nzrplans.orcon.net.nz/images/Aa1.jpg)

v t e Rail vehicles of New Zealand Diesel locomotives Mainline DA (inc. DAA, DAR) DB (inc. DBR) DC (inc. DCP) DF (English Electric) DF (General Motors) inc. DFT, DFB, DFM DG (inc. DH of 1956) DI DJ DL DM DQ and QR DX (inc. DXB, DXC, DXR) Shunt DE DH of 1978 DS DSA DSB DSC DSG DSH (on order) DSJ TR Electric locomotives 1500 V DC EA (later EO of 1968) EC ED EO of 1923 EW 25 kV AC EF Battery E EB Diesel multiple units ADK/ADB class diesel multiple unit ADL/ADC class diesel multiple unit Electric multiple units 1500 V DC (Wellington) "English Electric" DM (inc. D trailers) "Ganz Mavag" EM (inc. ET trailers) "Matangi" FP (inc. FT trailers) "Tūhono" BEMU (on order) 25 kV AC (Auckland) AM (inc. AMP, AMT, AMA) Railcars RM class 88 seater (also known as Fiats or twinsets) Clayton steam railcar Edison battery-electric railcar Red Terror railcar Midland railcar Leyland experimental petrol railcar McEwan Pratt petrol railcar Model T Ford railcar Sentinel-Cammell steam railcar Silver Fern railcar Standard railcar Thomas Transmission railcar Vulcan railcar Wairarapa railcar Westinghouse railcar Others A 88 Buckhurst petrol carriage Steam locomotives A of 1873 A of 1906 (inc. AD) AA AB B of 1874 B of 1899 BA BB BC C of 1873 C of 1930 D of 1874 D of 1929 E of 1872 & 1875 E of 1906 F FA (inc. FB) G of 1874 G Garratt of 1928 (inc. Pacific rebuild) H J of 1874 J of 1939 JA JB K of 1877 K of 1932 KA KB L LA M N NA NC O OA OB OC P of 1876 P of 1885 Q of 1878 Q of 1901 R S T U UA UB UC UD V W WA WAB WB WD WE WF WG WH WJ WS WW X Y Locomotive hauled carriages 50-foot carriage 56-foot carriage AC class (Grassgrubs) ex-British Rail Mark 2 carriage AK carriage FM class guards van SX carriages Track evaluation, cranes, and maintenance ETM class track evaluation car EL class rail cranes ETM class rail maintenance equipment Locomotives of New Zealand Rail transport in New Zealand Railway preservation in New Zealand.

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Adapted from the Wikipedia article [NZR AA class](https://en.wikipedia.org/wiki/NZR_AA_class) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/NZR_AA_class?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.