Production

Based on the success^[2] 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.^[1]

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 70 miles per hour (115 km/h),^[3] the A²was instrumental in the acceleration of timetables on many lines in the years following its introduction. A² locomotives famously ran the Geelong Flier,^[4] the first named train in Victoria,^[5] slashing journey times between Melbourne and Geelong from 90 minutes^[6] to 63^[7] and, finally, 55 minutes,^[8] a time not significantly improved upon until the introduction of 160 km/h Regional Fast Rail services in 2006.^[9]

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^[10] 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.^[11]

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.^[1] 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.^[12]

In 1933, two A² class locomotives set a haulage record for Victorian Railways when they headed a 75-truck 1,598-long-ton (1,624 t) wheat train from Benalla to Seymour.^[13]

Although initially limited to principal mainlines, due to their comparatively heavy axle load, gradual upgrades to secondary lines saw the route-availability of the class expand, together with the range of services they hauled.^[14]

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,^[15] 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.

Design Improvements

The majority of A² locomotives were originally built with saturated steam boilers. The class were gradually fitted with superheaters, 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. 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.

Experiments were conducted in 1923–4 with A² 800 using Pulverised Brown Coal (PBC) burning equipment, but the experiment was discontinued and the locomotive returned to black coal operation.^[16]

The A² class, along with other post-1900 VR steam locomotive designs, was equipped with electric lighting from 1926 onwards. Automatic Staff Exchange equipment to allow non-stop high-speed running between track sections was also fitted from 1926 onwards.^[17]

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. The results were very promising, and in 1934 A²998 was selected for a series of further tests aimed at further front end improvement, conducted under the direction of VR Rolling Stock branch engineer, Edgar Brownbill.^[18]

Diagram of A2 locomotive boiler, firebox and smokebox following Modified Front End improvements

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:^[18]

• Revision of exhaust nozzle and chimney position and diameter, using Wagner's recommended ratios, with a larger 23 in (580 mm) diameter funnel, and a 6 in (150 mm) diameter low exhaust nozzle replacing the original 18+1⁄2 in (470 mm) diameter narrow-flanged chimney and 5+1⁄2 in (140 mm) 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 1+3⁄8 in (35 mm) return bend superheater elements with 8 ft 6 in (2.59 m)-long 1+1⁄2 in (38 mm) elements

The sum result of the changes was a significant improvement in power and available tractive effort. Maximum drawbar horsepower increased about 40%, from 860 hp (640 kW) at 26 mph (42 km/h) to 1,230 hp (920 kW) at 32 mph (51 km/h).^[18] 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 100+3⁄4 mi (162.1 km) line being cut from 162 to 145 minutes, and literally hours being cut from the schedule of the Melbourne to Adelaide Overland express.^[19]

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 for VR.^[18][20]

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.^[15]

Stephenson A²884 (right) dwarfed by H 220 (left), the locomotive intended to replace the A² on Overland services

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.^[23]

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.^[14]

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.^[14] 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.^[14][24]

Stephensons engines

Walschaerts engines