GWR 6000 Class

The Great Western Railway (GWR) 6000 Class or King Class is a class of 4-6-0 steam locomotives designed for express passenger work and introduced in 1927. They were the largest locomotives built by the GWR, apart from the unique Pacific (The Great Bear). The class was named after kings of the United Kingdom and of England, beginning with the then reigning monarch, King George V, and going back through history. They handled the principal GWR expresses on the main line from London to the West of England and on the Chiltern line to Birmingham and Wolverhampton, until 1962 when the class was withdrawn.

Background and development
By 1918, it was apparent to the GWR chief mechanical engineer George Jackson Churchward that his Star Class 4-6-0 locomotives would soon be incapable of handling the heaviest West of England expresses without assistance. He therefore proposed fitting the 6 ft diameter boiler used on his 4700 Class 2-8-0 on to a 4-6-0 chassis, in 1919, to create a more powerful express locomotive, but was prevented from doing so by the weight restrictions on the GWR main line. The future problem was therefore left for his successor Charles Collett to solve.

On taking up office in 1922, Collett began to develop the more powerful Castle Class from Churchward's Star Class. However, the design was limited to a maximum axle-loading of 19.5 lt due to the weakness of some underline bridges. The new class would not therefore be able to pull express trains with more than thirteen coaches unaided. Following their introduction in 1923, the Castle Class was the most powerful express passenger class in the country in terms of tractive effort, but this honour was lost to the Southern Railway's Lord Nelson class in 1926.

The GWR's General Manager, Sir Felix Pole, was anxious for a new design that would once again enable the company to claim to run the most powerful locomotive. Pole agreed to allow Collett to explore a design for a "Super-Castle", subject to getting the tractive effort above 40,000 lbf. By 1927, a series of bridge renewals had taken place on the Great Western mainlines. This was coupled with the widely known (but as yet unpublished) findings of the Bridge Stress Committee, which gave engineers a better scientific understanding of the impact of hammer blow, and enabled the GWR Civil Engineer to agree to raise the maximum allowable axle-loading to 22.5 lt for the new ‘Super Castle’ class.

Design
Although Collett was nominally responsible for the design of the class, the detailed work was undertaken by his Chief draughtsman Frederick Hawksworth. The bulk of the increase in power over the Castle Class was initially achieved through raising the boiler pressure to a maximum of 250 psi and by increasing the cylinder stroke from 26 in to 28 in. These factors together increased the tractive effort to around 38165 lbf, slightly below the figure required by Pole.

As a means of increasing the tractive effort to bring it closer to the 40,000 lbf requested by Pole, smaller 6 ft 6 in (1.981 m) driving wheels were used compared to the standard 6 ft 8.5 in (2.045 m) on the "Castles" and the first six locomotives to be built had their cylinders bored out to 16.25 in giving a further 990 lbf, thereby enabling the ‘Kings’ to achieve a tractive effort of 40300 lbf. The smaller wheels also allowed for a wider boiler within the loading gauge to be used.

Later operational experience showed that loading gauge clearance of the outer cylinders was problematic, resulting in their replacement on each locomotive's first major overhaul, which resulted in a reduced tractive effort of 39700 lbf.

The new, 16 ft long, GWR ‘Standard No.12’ boiler was used on only this class. It had a maximum diameter of 6 ft tapering to 5 ft. There were 171 x 2+1/4 in fire tubes, and 16 x 5+1/8 in flue tubes. The firebox area was 194 sqft, with a tube area of 2008 sqft. As built, they had 96 × 1 in superheater tubes.

To accommodate larger inner cylinders the distinctive design of the leading bogie was adopted, with outside bearings on the fore wheel and inside bearings on the rear wheel.

Production
Twenty locomotives were ordered from the GWR Swindon Works in 1927 (Lot 243). The first locomotive No. 6000 King George V, appeared in June 1927. It was followed by five others (6001-6005) a month later. The remaining fourteen (6006-6019) appeared at almost weekly intervals between February and July 1928. A second batch of ten locomotives (6020-6029 Lot 267) appeared between May and August 1930.

No. 6007 King William III was written off after an accident near Shrivenham on 15 January 1936, and was condemned on 5 March 1936. A replacement was built (Lot 309) which may have incorporated some parts from the damaged locomotive; it took the same number and name, and was added to stock on 24 March 1936.

Naming
It was originally intended that the class be named after notable cathedrals, but, following an invitation to feature a GWR locomotive in the Baltimore and Ohio Railroad's (B&O) centenary celebrations, the GWR decided to make them more notable by naming the class after British Kings.

The class premier, No. 6000, was named King George V after the reigning monarch at the time, and the rest of the class would receive the names of English Kings in reverse order of ascendence to the throne. (ie. No. 6001 King Edward VII, No. 6002 King William IV...)

Following the death of King George V in 1936, No. 6029 King Stephen was renamed King Edward VIII after his successor; and following the abdication of the latter in the same year, No. 6028 King Henry II was renamed King George VI after the new King.

Operations
The class proved to be successful and able to cope with the heaviest express trains at a higher-speed timetable average than the "Castle". Due to their size and weight, the King class was however restricted to the London-Taunton-Plymouth (via both Bristol and Westbury) and the London-Birmingham-Wolverhampton (via Bicester) main lines. The class was therefore used on the GWR's crack expresses such as the Cornish Riviera Limited until the end of regular steam hauled express services on the Western Region of British Railways, although they needed assistance for the heaviest services over the South Devon Banks between Newton Abbot and Plymouth. They were unable to serve in Cornwall, due to the weakness of the Royal Albert Bridge, and so when they were hauling the Cornish Riviera Limited, they had to be swapped for a 'Castle' or 'Hall' at Devonport.

King George V in the United States
After six months of operation, No. 6000 was shipped to North America in August 1927 to join in Baltimore & Ohio Centenary celebrations, where its sleek appearance and smooth performance impressed all who witnessed it. King George V was presented with a brass bell and cabside medallions to mark the occasion. The application of pressurised oil lubrication showed its advantages over the largely grease-lubricated American Locomotives, and was even incorporated into a later design for the B&O in 1928.

Further developments
No. 6014 King Henry VII was partially streamlined in March 1935 with a hemispherical smokebox door, continuous splashers, straight nameplate, smooth running plate and a swept-back cab front, which was carried out so that the GWR would have a streamlined locomotive to promote against the upcoming Gresley A4 Pacifics. This was designed more for aesthetics rather than speed however, and would only give the most basic improvements in aerodynamics. The appendages were soon removed sometime prior to January 1943, with the exception of the cab which would be retained on the locomotive until 1953.

The class proved to be capable and reliable when using the high-calorific South Wales steam coal, on which the GWR had always relied for its good locomotive performance. However, during the 1948 locomotive exchanges, King Henry VI performed disappointingly using Yorkshire coal, despite demonstrating the 4-6-0 type's unique sure-footedness when climbing out of Kings Cross, where pacific types were apt to slip alarmingly.

As originally built the class had a Swindon superheater with an area of 313 sqft. However, in 1947 experiments were undertaken with a four-row high-degree superheater in No. 6022 King Edward III. As a result, the four-row superheaters were fitted to the whole class, and modifications were also made to the draughting arrangement, using No. 6001 King Edward VII as a test-bed. From September 1955, double blast-pipes and chimneys were fitted, initially to No. 6015 King Richard III. Following successful testing the whole of the class was subsequently modified and, as a result, their final years in British Railways ownership saw the very best of their performance, particularly on the steep South Devon Banks at Dainton, Rattery, and Hemerdon.

Accidents and incidents
There have been two serious accidents involving the class:
 * On 10 August 1927, the leading bogie of, then new, 6003 King George IV, became derailed at speed approaching Midgham. This led to the suspension arrangement of the unusual bogie being improved.
 * On 15 January 1936, a freight train, hauled by GWR 2800 Class 2-8-0 No. 2802, became divided at Shrivenham, Berkshire. Due to errors by the guard of the freight train and a signalman, an express passenger train hauled by No. 6007 King William III ran into the six wagons that had been left behind and derailed. Two people were killed. As a result, the locomotive was written off and replaced by another with the same name and number.
 * On 4 November 1940, an express passenger train hauled by No. 6028 King George VI was derailed at Norton Fitzwarren, Somerset due to the driver misreading signals. Twenty-seven people were killed and 57 were seriously injured.

List of King Class locomotives
Thirty-one locomotives were built at Swindon, although only 30 were in service simultaneously:

Preservation
As a result of its previous broad-gauge system, the GWR had the largest loading gauge of all the pre-nationalisation railways in the UK. To allow for maximum power creation and resultant speed, the GWR designed the King class to its maximum mainline loading gauge, specifically a maximum height allowance of 13 ft. Consequently, this restricted them as to where they could operate under both GWR and British Railways ownership.

No. 6018 King Henry VI was the subject of preservation by Sir Billy Butlin, but the plans never came to fruition and the locomotive was scrapped. Famous film actor Kenneth More expressed a desire to save the locomotive, but those plans never came into fruition.

In 1962, the recently withdrawn 6023 King Edward II and 6024 King Edward I were both initially sent to Swindon to be broken up for scrap, but, in light of a new railway bridge being installed west of Bristol, the two locomotives were coupled together and taken to the bridge for weight testing purposes. After the completion of the tests, the locomotives were sent to Woodham Brothers scrapyard at Barry, which would involve less travelling than travelling back to Swindon. This locomotive movement likely saved the locomotives from scrapping.

Developments in high-speed rail from the 1970s mean that ballast depths have increased, resulting in a present decrease in UK pan-network loading gauge height. This has recently started to be reversed with the introduction of pan-European loading gauge standards on some mainlines, mainly originating from ports. The present result of these civil engineering changes is that an original height King locomotive would not pass through various points of the modern Network Rail system, designed to a loading gauge height of 13 ft.

All three preserved Kings have been on the mainline in preservation but only 6000 King George V and 6024 King Edward I have operated on the main line.

Faced with a choice of either not operating their locomotives on the mainline or modifying to allow them to pass within the current restricted UK loading gauge, private societies choose to reduce the height of their locomotives by 4 in by: reducing cab and chimney height; modifying some upper pipe work. The National Railway Museum, owners of 6000 King George V, decided to keep this locomotive in its original condition.

Civic heraldry
The Borough of Swindon commissioned a new coat of arms when it became a unitary authority in 1997. The coat of arms includes an image of 6000 King George V on the shield, recognising the importance of the Swindon works in the development of Swindon. The coat of arms of the old Borough of Swindon (1900–74) included an image of GWR 3031 Class 3029 White Horse.