Victorian Railways A2 class. The A2 class was an express passenger locomotive that ran on Victorian Railways from 1907 to 1963. A highly successful design entirely the work of Victorian Railways' own design office, its long service life was repeatedly extended as the Great Depression and later World War II delayed the introduction of more modern and powerful replacement locomotives.

History
The introduction of the A2 class marked a turning point in Victorian Railways locomotive design, as it was entirely designed by VR engineers of the newly established Locomotive Design Section and the entire class built in-house at Victorian Railways workshops.

The design, which started as a stretched evolution of the 1903 AA Class 4-4-0 with bogie tender, has been credited to Chief Draughtsman Ernest Victor Siepen, with overall supervision of Chief Mechanical Engineer T. H. Woodroffe.; previously this had been attributed to Alfred Ernest Smith, a later Chief Mechanical Engineer.

Production
At this time, the Sydney Express was regularly double-headed in both directions between Melbourne and Seymour, due primarily to the gradients either side of the Great Dividing Range. A2 572 was trialled on this run and others for about a year, with minor improvements undertaken as they were found to be necessary. These included an altered design of forward frame stiffener (between the smokebox and leading bogie), additional bolts to hold the cylinders in place against the thrust of the pistons, and an additional cradle under the firebox backplate end of the boiler. However, the engine retained its distinctive flat-topped dome. Five more of the class, 574, 576, 578, 580 and 722, were ordered in 190, and production continued from them on.

Based on the success of the prototype A2572, a total of 125 Stephenson valve gear A2 locomotives were built between 1907 and 1915. The design was then altered to incorporate larger diameter cylinders, a higher pressure boiler and Walschaerts valve gear, and a further 60 locomotives of that design were produced between 1915 and 1922.

Regular service
For over forty years, the A2was the main express passenger locomotive on the VR, hauling intrastate and interstate services. With a maximum permitted speed of , the A2was instrumental in the acceleration of timetables on many lines in the years following its introduction. A2 locomotives famously hauled the Geelong Flier, the first named train in Victoria, which ran express once a day in each direction between Melbourne and Geelong in 63 minutes, running from Flinders Street station,  later cut to 55 minutes, running from Spencer Street station. However, other Geelong trains, stopping at wayside stations, still took about 90 minutes or more to make the journey.

Due to their comparatively heavy axle load, A2 locomotives were initially limited to the principal mainlines, but gradual upgrades to secondary lines saw the route-availability of the class expand, together with the range of services they hauled. Their size also meant that the outside cylinders of the new locomotives did not quite clear the stone or timber coping of some existing station platforms, requiring those platform edges to be cut back slightly to allow the locomotives to pass safely.

With their comparatively high tractive effort (the Walschaerts A2 had a higher nominal tractive effort than any other VR locomotive, regardless of type, until the introduction of the C class 2-8-0 of 1918), they also saw widespread use as a fast goods locomotive, particularly later in their life. As early as the 1920s, it was reported as normal practice that A2 class locomotives requiring adjustment to axle boxes and other moving parts be swapped from passenger to lower-speed freight service to extract more work from them between overhauls. Reportedly, engine crews preferred the Stephenson engines for fast running, but Walschearts locomotives for heavy haulage, based on the ride quality.

A2s were also used to haul a number of special services, such as the Royal Trains for Australian tours of Prince of Wales and the Duke of York, in 1920 and 1927 respectively. Towards the end of their lives, A2995 and 996 also had the distinction of hauling the last broad gauge Spirit of Progress service into Melbourne on 16 April 1962.

In 1928, the A2 was replaced on the principal North East line Sydney Limited and Albury Express services by the considerably more powerful three-cylinder S class Pacifics. However, new locomotive development ground to a halt during the 1930s, with the Great Depression severely affecting both VR traffic volumes and operating revenues, so the A2 continued to be the main express passenger power on all other VR mainlines.

In 1933, two A2 class locomotives set a haulage record for Victorian Railways when they headed a 75-truck  wheat train from Benalla to Seymour.

Pairs of A2 class engines were regularly worked on the Melbourne-Ararat and Ararat-Serviceton portions of The Overland; common candidates included A2940, A2942, A2947, A2955, A2966, A2973, A2976, A2993 and A2994.

Design Improvements
Changes to the locomotive and tender designs slightly increased the roadworthy weight of engine and tender combined from  to , and the maximum axle load increased by about a quarter-ton. The Walschearts design was heavier again, with a roadworthy weight of , and maximum axle load of .

Superheaters
The majority of A2 locomotives were originally built with saturated steam boilers. The class were gradually fitted with superheaters (starting from A2842, built 1913, fitted 1915), and to differentiate between the two variants the saturated steam locomotives were renumbered as A1 class, each being reclassified as A2 class again when fitted with a superheater. The order to reclassify saturated engines to A1 was issued on 16 March 1929 and applied to 70 engines, but some of these were still carrying A2 plates in 1932.

All Walschaerts locomotives were intended to enter service with superheated boilers, but wartime shortages meant that of the first fifteen (983 to 997), only 991 and 992 were issued to service with superheated boilers., the others running with saturated boilers for a few years. As these engines were refitted, the cylinders were replaced to achieve a  diameter, though thestroke length of  was retained. Other changes included reducing the boiler pressure from  to  at 80% of maximum safe rated pressure, offset by the fitting of superheaters. The first engine upgraded was A2 820, and the work involved provision of new cylinder castings rather than reboring the prior set. Notably, around 1930, an Interstate Commissioners Conference agreed that superheated engines' tractive effort was to be calculated at 85% of maximum safe boiler pressure, against 80% for saturated engines.

The superheating equipment was of either the Robinson () or Schmitt () designs, either applied to the new-build Walschaerts locomotives. Engines upgraded were fitted with Robinson superheaters until 1929. From then, a new all-steel boiler and firebox was designed (in lieu of the prior copper inner firebox lining), and this style used ML5 equipment in lieu (); the steel boiler was interchangeable between the Stephenson and Walschaert locomotives, contingent on the safety valves being correctly set. Superheated engines were also fitted with mechanical lubricators.

Many engines were renumbered two or three times as the railways' management attempted to keep the two subclasses in different number blocks, and as the boundaries between the blocks shifted through the superheating program. The last of the A1 class, No. 808, was converted in October 1949.

Modified front end
In 1933, C class heavy goods locomotive C 5 was equipped with a new front end, based on the Association of American Railroads (AAR) design of self-cleaning smokebox, to improve steaming qualities. This was an evolution of design updates provided to the S and X Class engines from 1928, including requiring only one spark-arresting grate through the year, rather than needing a second grate in summer. These changes netted a 23% increase in power output at . Victorian Railways' Rolling Stock branch engineer Edgar Brownbill continued this work from May 1933, conducting tests with A2 974 between Melbourne, Bendigo and Seymour with  diameter superheater tubes, for a net improvement of 40% increased drawbar horsepower at . These results were very promising, and in April 1934 A2998 was selected for a series of additional tests aimed at further front end improvement. These tests involved various chimney-choke-point and blastpipe nozzle diameter sizes, ranging from  to  and  to  respectively. In September 1934, A2989 was the first to be fitted with the standard form of Modified Front End, and it completed a run from Bendigo to Spencer Street in 2 hours 10 minutes; A2 993 was the next converted, and the first with smoke deflectors fitted in November 1934.

Experiments were conducted, based on the work of Dr Wagner of the Deutsche Reichsbahn and E. C. Young of the University of Illinois, with final modifications to the A2 locomotive including:
 Revision of exhaust nozzle and chimney position and diameter, using Wagner's recommended ratios, with a larger  diameter funnel, and a  diameter low exhaust nozzle replacing the original  diameter narrow-flanged chimney and  diameter high exhaust nozzle
 Revision to the firebox grate, using a "rosebud" type grate with reduced air openings to improve fire stability under heavy load and give better firing qualities
 Replacement of full-length  return bend superheater elements with -long  elements

The sum result of the changes was a significant improvement in power and available tractive effort. Maximum drawbar horsepower increased about 40%, from  at  to  at . The improvement was such that the VR was able to further accelerate services hauled by the A2, with the running time of the Melbourne to Bendigo express on the steeply graded  line being cut from 162 to 145 minutes, and literally hours being cut from the schedule of the Melbourne to Adelaide Overland express.

However, a more recent review indicates that more appropriate exhaust values may have been  to  for the chimney choke point and  to  for the blastpipe nozzle diameter; and that suitable designs could have been adapted to the pre-existing chimney of the A2 class locomotive, without the later need to provide smoke deflectors.

The Modified Front End, which cost just £140 ($280) per locomotive at that time, was an extremely cost-effective improvement, and allowed the VR to defer new locomotive construction. The modification was so successful that not only was the entire A2 fleet converted during 1936–39, but also the C, K, N, S and X class locomotive fleets, and its principles were also incorporated into the design of all subsequent steam locomotives built or modified for the Victorian Railways.

Tenders
Then first forty engines built between 1907-1911 were fitted with Type AD tenders of capacity  coal and  water; these tanks sat on a frame with  bogie centres; this was distinct from the AA class locomotive tenders, which had  bogie centres but were  shorter behind the rear bogie than the Type AD. The bogies were identical to those used on the V and last of the AA class engines, with split-spoke wheels of  diameter. These tenders later had the sides extended to increase the coal capacity to  tons; some had their official water capacity listed as  gallons. The Type AD tenders were swapped between A2 and DD series engines as required, with D2766, A2866, A2893, A2910 and A2923 each being noted as having a short-frame tender with extended sides at some point before 1958. Similar short, self-trimming tenders were provided to the first ten K Class locomotives when they entered service; from that point the short tenders were noted as Type DK. The last of the flat-top tenders were fitted to A2 913 and 939.

Engine A2799 was the first fitted with a self-trimming tender in 1912, such that coal would naturally fall down the bunker towards the footplate as space was freed up; this avoided the fireman having to regularly climb up the top of the tender to push coal forward for later use.  This design had capacity for  coal and  water, and was applied to all future A2 class locomotives as they were built. A similar, but shorter and reduced capacity, version of this design was provided for the DD class locomotives delivered from Walkers, Queensland in 1913. All self-trimming tenders had solid-spoke wheels of  diameter. Some of the A2, C and N class self-trimming tenders had their coal capacity similarly increased around 1931; in this format they were registered as  coal and  water, though it is unlikely that any Type CN tenders were used on A2 locomotives or vice-versa. Generally speaking, ex-A2 tenders could be distinguished from ex-C and N Class tenders by former having square-cut rear ends of the extended sides; the shorter length of the A2 tenders being less obvious.

A new standard self-trimming tender was introduced for the A2 fleet in 1933, mostly using Type AD frames from scrapped DD-series locomotives; all such frames were  long, and not altered. The new tank was straight-sided, with earlier instances being rivetted and later units welded. The capacity was for  coal and  water, and through the decade older tenders were replaced or modified with this design. These were the New Type AD tenders, and they were also given to D3 locomotives from 1935. To accommodate the increased axle load strengthened bogies were provided, fitted with solid-spoked wheels of an over-tyre diameter of  diameter. Smaller versions of these tanks were built for the New Type DK tenders from 1940, provided to new build K Class and refurbished D1, D2 and D3 locomotives; these had a capacity of  coal and  water, though later versions were shown as  coal and  water.

The final development was the creation of an all-welded tender tank, designed for tender frames of  length with  bogie centres. These were known as the Type ACN, were similar to the rivetted tenders provided to the Newport-built 1930/31 N Class locomotives, and were used on the A2, C and N Class engines interchangeably. They had capacity for  coal and  water.

Other changes
The original five locomotives had their Westinghouse air brake compressors mounted on the right-hand side of the firebox; all later engines had this changed to the smokebox, and within a few years the first five were amended to suit.

A2 1072 was the last engine built at Newport to be painted Canadian Red; the next engine, C 2, was the first painted black. It is not known whether the ten subsequent A2 engines built at Ballarat and Bendigo were painted red or black on entry to service.

In 1922-1923 the Victorian Railways experimented with Precipitated Brown Coal, using locomotives A2800, C16 and DD1022. After completion of the trials, all three engines reverted to black coal firing. A photo of the engine with the modified tender appears in Newsrail, November 1983, p. 295.

May 1926 saw a Pyle National electric headlight, marker, cab and tender lights fitted to locomotive A2978, and this was rolled out to all A2 and many other classes of engine in subsequent years, generally operated by a Pyle or Stone generator mounted ahead of the safety valves. Also around this time, Automatic Staff Exchange equipment was fitted to allow non-stop high-speed running through stations, where trains would otherwise have needed to slow down or stop for manual token exchanges.

In June 1933, A2970 was fitted with an improved type of exhaust steam injector on the fireman's side; this was later compared to the 1935 fitting of an experimental A.C.F.I. (Accessoires pour les Chemins de Fer et l'Industrie) feedwater heater to A2973. However, there was not sufficient improvement in efficiency for the equipment to be fitted to other locomotives and the latter was removed twelve years later, in 1947. The equipment was, however, retained for significantly longer than equivalent experiments by the New South Wales, Commonwealth and Western Australian Railways. While fitted with the A.C.F.I. equipment, A2973 was generally allocated to the Bendigo line. After the equipment was removed, the engine was reallocated and often ran trips on The Overland.

With the reduced exhaust blast resulting from the revised smokebox, smoke deflectors were fitted to prevent drifting smoke from obscuring visibility.

By the 1930s the original plate frames of the A2 class had proven prone to cracking, particularly around the axle box cut-outs and the draw-gear (coupler) pockets. This resulted in at least five, possibly ten, engines being reframed with American-style bar frames in the period 1939-1945. (Australian Railway History 2019 lists five engines, Newsrail November 1983 says ten engines but does not specify which.)

In the years following World War II, problems with the quality and availability of coal supplies caused VR to order the conversion of all 60 Walschaerts A2s to oil firing; in practice, only 56 were altered as four were scrapped before the conversion could be completed.  A2 942 was the first to be modified, being provided with a  gallon square oil tank fitted to the coal space of the tender. This style was selected to permit reconversion to coal burning if required. When it became apparent that oil burning was a permanent conversion, a new cylindrical tank design with  capacity was provided, that style also later rolled out to C and N Class locomotives. Additional benefits included less time needed for enroute engine maintenance, e.g. breaking up clinker in the firebox and dumping of ash. These tanks later had steam heating coils fitted, to allow the use of cheaper Bunker C oil. Engines thought to have been fitted with the square-type oil tank included 940-941, 943-955, 957, 969, 971-974, 976-997 and 999.

Late in their life, some of the A2s also received Boxpok driving wheels as their conventional spoked wheels began to suffer fatigue cracks with age and mileage. These wheels were reputed to give the engines a very rough ride, but apparently reduced the amount of maintenance required to the axle boxes. In July 1951, engine A2888 was fitted with a different style of driving wheel, described as "fabricated welded", but restricted to freight work from that point on. A photo of these latter driving wheels appears in Newsrail, November 1983, p. 295.

Six Stephenson engines were fitted with shunters steps in the mid 1950s. This alteration may have been timed with the fitting of sand boxes for tender-first operation.

Other alterations not noted above included fitting of Flaman speed recorders, solid bush big ends and hard grease lubrication, exhaust steam injectors (for a while), flanged smokebox doors, automatic couplers, conversion to all-steel boilers (most locomotives), trick-ported valves on A2963, Cardew track depression indicator gear on A2980 and later A2951, and tender scale buoy and continuous blowdown for A2875. Some of the last changes involved fitting of integral water treatment units to the tenders, with a blow-down valve operated manually from the cab. This arrangement pulled sludge down to the boiler firebox water legs, allowing it to be discharged at regular intervals instead of needing to cool down and manually wash out the boiler.

Later years
In 1939, by which time most of the class was already over twenty-five years old, World War II broke out. The massive increase in traffic on the VR the war effort brought saw these ageing locomotives subjected to a punishing regime of heavy utilisation and minimal maintenance.

With VR's locomotive workshops switched to production of armaments and all available manpower given to the war effort, plans to eliminate the double-headed A2 operations on Melbourne–Adelaide passenger services with the introduction of more powerful H class 4-8-4 locomotives and additional S class locomotives did not come to fruition. The extra S class locomotives were never built and the line to Adelaide did not receive the necessary upgrades to take the weight of the H class.

The A2's principal express passenger role continued into the postwar years as the VR, struggling with a backlog of repairs and limited capital expenditure, deferred new passenger locomotive construction. It was not until March 1946 when the first of the class, A2878, was withdrawn from service.

In 1951, when the first of 70 new R class 4-6-4 express passenger locomotives were introduced, the A2 was finally superseded. In 1953, no fewer than 53 A2s went to scrap, followed by 36 more in 1954. However, many of the class (particularly the later Walschaerts variants) continued on in secondary roles such as branch-line passenger and goods services and a number lasted into the 1960s. Their last regular mainline duty was hauling services between Flinders Street and Leongatha, on the South Gippsland line. The last in service, A2986, was withdrawn on 2 December 1963, exactly 56 years after the original A2572 entered service.

Accidents 
Some A2 locomotives were unfortunate enough to be involved in major accidents:
 At 2:58am on 7 September 1951, the westbound and eastbound Overland expresses, both hauled by double-heading A2s, collided head-on at Serviceton. All four locomotives were written off; three were so badly damaged they were scrapped on site.
 Wodonga level crossing accident: Australia's worst level crossing accident occurred on 8 May 1943, when A2863 collided with a bus carrying troops at Wodonga. 25 people were killed.

List of engines and renumberings

The A2 fleet was constructed in ten batches. All the Stephenson engines, batches 1 to 8, were constructed at the Victorian Railways' Newport Workshops. The same is true of Batch 9 and the first 20 engines of Batch 10. However, engines 1073–1077 (later 973–977) were built at Ballarat Workshops, and 1078–1082 (later 978–982) were built at Bendigo Workshops. There is no indication as to where engines 1083–1092 would have been constructed.

Except where otherwise marked, these tables are based on:
 Australian Railway History, August 2019
 Australian Railway History, August 2019 (Web extra)
 Medlin, P. N. (2004) Victorian Railways Locomotives by Number (self-published, based on Victorian Railways' locomotive repair cards)
 Victorian Railways locomotive record cards

Stephensons engines

Walschaerts engines

Preservation 

Only one of the original batch of 125 Stephenson A2 locomotives survives; 1913-built A2884 is today preserved at the Newport Railway Museum, along with (Walschaerts) A2995. The museum notes that A2884 ran a total  and A2995 a total  during their service lives.

A2964 is preserved at Edwardes Lake Park, Reservoir and A2996 in Echuca.

After a 32-year-long effort, Steamrail Victoria restored A2986 to full working order as a coal burner. It first moved under steam on 30 May 2015 and entered service with Steamrail on 13 May 2017.

References

External links 
 Dee et al., Power Parade, VicRail Public Relations Division, Melbourne, 1981, 
 Pearce et al., North Williamstown Railway Museum, ARHS, Melbourne, 1980, 
 The Recorder, ARHS, Adelaide, November 1985, 
 AHRS Railway Museum History 1900–1950 retrieved on 6 September 2006
 National Library of Australia Photograph of prototype A2572, December 1907
 victorianrailways.net Stephenson A2936 hauling a goods train, 11 June 1930.
 victorianrailways.net Walschaerts A2973 leads a Stephenson A2on The Overland, circa 1930
 Public Record Office Victoria Classic VR photograph of A2-hauled passenger train with E type carriages crossing the Malmsbury Viaduct, 1945
 Public Record Office Victoria – A2856 is cut up for scrap.
 victorianrailways.net A2986, seen around 1962 near the end of its service life. Various modifications over the years have significantly altered its appearance from when photographed in 1916 (see top of this page)
 Steamrail A2986 page Photos detailing the progress of current restoration work on A2986

4-6-0 locomotives
Railway locomotives introduced in 1907
Preserved steam locomotives of Australia
Broad gauge locomotives in Australia
A2 class 1907
Ballarat North Workshops locomotives
Bendigo Workshops locomotives
Newport Workshops locomotives
Passenger locomotives