NZR AA class

{{Use New Zealand English|date=July 2024}} {{Use dmy dates|date=July 2019}} {{DISPLAYTITLE:NZR A^A class}} {{Infobox locomotive | name = NZR A^A class | powertype = Steam | image = Aa class steam locomotive (NZR number 650, 4-6-2) ATLIB 257167.png | caption = No. 650 at [[Petone railway station|Petone]] between 1915 and 1920 | builder = [[Baldwin Locomotive Works]] | serialnumber = | builddate = 1915 | totalproduction = 10 | whytetype = [[4-6-2]] | gauge = {{Track gauge|42in|lk=on}} | driverdiameter = {{convert|49|in|m|3|abbr=on}} | length = {{convert|34|ft|9|in|m|2|abbr=on}} | width = | height = | axleload = | weightondrivers = {{long ton|34|14}}<br>{{convert|34|LT|14|lcwt|t ST|abbr=on|lk=on}} | locoweight = | tenderweight = | locotenderweight = {{convert|88.5|LT|t ST|1|abbr=off}} | fueltype = [[Coal]] | fuelcap = | watercap = | firearea = {{convert|28.3|sqft|m2|abbr=on}} | totalsurface = {{convert|1465|sqft|m2|abbr=on}} | boilerpressure = {{convert|170|psi|MPa|2|abbr=on}} (as coumpound) | cylindercount = 2 | cylindersize = {{convert|18|x|24|in|mm|0|abbr=on}} | tractiveeffort = {{convert|21580|lbf|kN|abbr=on}} | maxspeed = | preservedunits = | operator = [[NZGR]] | fleetnumbers = 648 - 657 | locale = | withdrawndate = 1955–1957 | disposition = All [[scrap]]ped }} The '''NZR A^A class''' consisted of ten [[steam locomotive]]s built by [[Baldwin Locomotive Works]] in 1914 to an order by Chief Mechanical Engineer, H. H. Jackson for operation on [[New Zealand]]'s [[Rail transport in New Zealand|national rail network]]. 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 [[NZR Q class (1901)|Q class]] of 1901, they had a wheel arrangement of [[4-6-2]] 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]] 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 [[New Zealand Railways Department|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.{{sfn|Millar|2011|p=}}

== 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]] coal meant a larger grate was desirable.{{sfn|Millar|2011|p=}} 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 [[Second World War]]. They were used extensively on the steeply graded central [[North Island Main Trunk]], [[Marton–New Plymouth Line|Wanganui]] and [[Palmerston North–Gisborne Line|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.{{sfn|Palmer|Stewart|1965|p=103}} None were preserved.

==See also== * [[NZR Q class (1901)]] * [[NZR A class (1906)|NZR A/A^D class (1906)]] * [[NZR AB class|NZR A^B class]] * [[NZR G class (1928)]] * [[Locomotives of New Zealand]]

==References== ===Citations=== {{reflist}}

=== Bibliography === {{refbegin}} *{{cite book|title=Register of New Zealand Railways Steam Locomotives 1863-1971|first=W. G.|last=Lloyd|year=1974|edition=2nd|ISBN=0-9582072-1-6}} *{{NZR Steam Locomotive}} * {{When Steam Was King}} * {{Palmer & Stewart}} {{refend}}

== External links == * [http://www.baldwin-steam.org.nz/loco/classes.html Baldwin Steam Trust - New Zealand locomotives built by Baldwin, including A^A class statistics] * [http://nzrplans.orcon.net.nz/images/Aa1.jpg Plan of an A^A class locomotive by Derek Brown]

{{NZR Locomotives}}

[[Category:Steam locomotives of New Zealand|Aa class]] [[Category:4-6-2 locomotives]] [[Category:2′C1′ locomotives]] [[Category:Baldwin locomotives]] [[Category:Scrapped locomotives]] [[Category:Freight locomotives]] [[Category:Railway locomotives introduced in 1915]] [[Category:3 ft 6 in gauge locomotives of New Zealand]]

{{NewZealand-rail-transport-stub}}