In 1922, after the SAR's worst financial deficit, the government appointed American railroad manager William Webb, from the Missouri-Kansas-Texas Railroad as Chief Commissioner.
When Webb arrived in Adelaide with his young family, he found a railway system unchanged since the late 19th century.
The locomotives and rolling stock were small, wagons and carriages were of wooden construction, the track and bridges were unsuitable for heavy loads, the workshops had antiquated machinery and the signalling system was inflexible.
These attributes drove up the ratio of operating costs to revenue.

Webb introduced a rehabilitation plan based on American railroad principles of large, standardised locomotives and steel bodied freight wagons, with automatic couplers to enable a significant increase in productivity.
Lightly patronised passenger trains would be replaced by self-propelled rail cars, enabling faster, more frequent and more efficient services.
He recruited Fred Shea as his Chief Mechanical Engineer and had him prepare specifications for this new equipment.
This resulted in orders being placed for 1,200 wagons of four types from American Car and Foundry, 12 petrol mechanical railmotor cars from the Service Motors Corporation, Wabash, Indiana, and 30 locomotives based on American Locomotive Company plans but built by Armstrong Whitworth & Co in the United Kingdom.
These were of the Mountain, Pacific and Mikado wheel arrangements, 10 of each type, which became the 500, 600, and 700 class locomotives.

To carry the heavier trains, the rehabilitation plan included the strengthening of track and bridges, and the conversion of the mid north 3 ft 6 in (1,067 mm) narrow gauge system (the Western division) to 5 ft 3 in (1,600 mm) broad gauge.
The antiquated Islington Railway Workshops were demolished and replaced with a thoroughly modern railway maintenance and manufacturing works, a large new round house was built at Mile End, near Adelaide, and several 85 foot turntables were installed throughout the state to enable the much larger locomotives to be turned.
Efficient train operations were facilitated by the adoption of American train order working on country lines, and Adelaide railway station was replaced with an imposing new building, opened in 1927.
This grand building has been partially taken over by the Adelaide Casino.

When the two shiploads of new locomotives arrived in 1926 they caused a sensation with the public and throughout the railway industry in Australia.
The 500 class "Mountain" was over twice the size of the biggest pre-Webb engine, and was the most powerful locomotive in Australia.
Henceforth double heading 5 ft 3 in (1,600 mm) broad gauge trains became a rarity in South Australia.
The massive locomotives were unloaded at Port Adelaide and taken off the pier by horses (the locomotives weight alone exceeding the dock's maximum loading capacity).
Apart from some initial teething problems (mainly to do with overheating bearings and rough riding due to excessive play allowed on driving axles) the new locomotives settled in nicely to their assigned positions.
After the success of the original locomotives, ten more 700 class locomotives, with larger tenders, were locally built using the facilities of the new Islington Workshops.
These were the 710 class.

The 500 class was rated to haul 400 tons over the Mount Lofty Ranges immediately east of Adelaide, where a 19-mile (31 km) continuous 1-in-45 (2.2%) gradient faced trains heading for Victoria.
Two years after their introduction, the class was modified by the addition of a booster engine which required replacement of the two-wheel trailing truck with a four-wheel truck.
This altered the wheel arrangement from 4-8-2 to 4-8-4, but the term "Mountains" stuck with the locomotives.
Reclassified 500B class, their maximum load to Mount Lofty was increased to 600 tons, or eleven passenger cars.
In the pre-Webb era the Rx class - a 4-6-0 with a Belpaire firebox was rated at 190 tons for this line, with three of them required to lift a heavy Melbourne Express - two at the front an
In 1922, after the SAR's worst financial deficit, the government appointed American railroad manager William Webb, from the Missouri-Kansas-Texas Railroad as Chief Commissioner. When Webb arrived in Adelaide with his young family, he found a railway system unchanged since the late 19th century. The locomotives and rolling stock were small, wagons and carriages were of wooden construction, the track and bridges were unsuitable for heavy loads, the workshops had antiquated machinery and the signalling system was inflexible. These attributes drove up the ratio of operating costs to revenue.
Webb introduced a rehabilitation plan based on American railroad principles of large, standardised locomotives and steel bodied freight wagons, with automatic couplers to enable a significant increase in productivity. Lightly patronised passenger trains would be replaced by self-propelled rail cars, enabling faster, more frequent and more efficient services. He recruited Fred Shea as his Chief Mechanical Engineer and had him prepare specifications for this new equipment. This resulted in orders being placed for 1,200 wagons of four types from American Car and Foundry, 12 petrol mechanical railmotor cars from the Service Motors Corporation, Wabash, Indiana, and 30 locomotives based on American Locomotive Company plans but built by Armstrong Whitworth & Co in the United Kingdom. These were of the Mountain, Pacific and Mikado wheel arrangements, 10 of each type, which became the 500, 600, and 700 class locomotives.
To carry the heavier trains, the rehabilitation plan included the strengthening of track and bridges, and the conversion of the mid north 3 ft 6 in (1,067 mm) narrow gauge system (the Western division) to 5 ft 3 in (1,600 mm) broad gauge. The antiquated Islington Railway Workshops were demolished and replaced with a thoroughly modern railway maintenance and manufacturing works, a large new round house was built at Mile End, near Adelaide, and several 85 foot turntables were installed throughout the state to enable the much larger locomotives to be turned. Efficient train operations were facilitated by the adoption of American train order working on country lines, and Adelaide railway station was replaced with an imposing new building, opened in 1927. This grand building has been partially taken over by the Adelaide Casino.
When the two shiploads of new locomotives arrived in 1926 they caused a sensation with the public and throughout the railway industry in Australia. The 500 class "Mountain" was over twice the size of the biggest pre-Webb engine, and was the most powerful locomotive in Australia. Henceforth double heading 5 ft 3 in (1,600 mm) broad gauge trains became a rarity in South Australia. The massive locomotives were unloaded at Port Adelaide and taken off the pier by horses (the locomotives weight alone exceeding the dock's maximum loading capacity). Apart from some initial teething problems (mainly to do with overheating bearings and rough riding due to excessive play allowed on driving axles) the new locomotives settled in nicely to their assigned positions. After the success of the original locomotives, ten more 700 class locomotives, with larger tenders, were locally built using the facilities of the new Islington Workshops. These were the 710 class.
The 500 class was rated to haul 400 tons over the Mount Lofty Ranges immediately east of Adelaide, where a 19-mile (31 km) continuous 1-in-45 (2.2%) gradient faced trains heading for Victoria. Two years after their introduction, the class was modified by the addition of a booster engine which required replacement of the two-wheel trailing truck with a four-wheel truck. This altered the wheel arrangement from 4-8-2 to 4-8-4, but the term "Mountains" stuck with the locomotives. Reclassified 500B class, their maximum load to Mount Lofty was increased to 600 tons, or eleven passenger cars. In the pre-Webb era the Rx class - a 4-6-0 with a Belpaire firebox was rated at 190 tons for this line, with three of them required to lift a heavy Melbourne Express - two at the front an
South Australian Railways