GWR 6000 Class

Development requirements

After developing the new GWR Castle class from George Jackson Churchward's GWR Star class, Chief mechanical engineer C.B. Collett was faced with the need to develop an even more powerful locomotive to pull 13+ carriage express trains. Resultantly, during planning and construction, the new engine design was dubbed the "Super-Castle".

Collett successfully argued with the GWR's General Manager, Sir Felix Pole, that had the axle-loading restriction of 19.5 long tons (19,800 kg) of the "Castle" class been increased to the maximum allowable of 22.5 long tons (22,900 kg), an even more powerful locomotive could have been created. Pole agreed to allow Collett to explore such a design, subject to getting tractive effort above 40,000 lbf (180,000 N).

As well as to meet future traffic requirements, the design requirement was also a response to the GWR's publicity department's desire to regain the title of having the "most powerful express passenger steam locomotive in Britain", which had been taken from the Castle Class in 1926 by the Southern Railway Lord Nelson Class.

Design

Churchward had proposed fitting the 6 ft (1.83 m) 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 had been prevented from doing so due to weight restrictions on several bridges on the GWR main line. Collett's "Castle" class of 1923 was therefore a compromise with a 5 ft 6 in (1.68 m) boiler. However, bridge strengthening and a better understanding of the effect of hammer blow on structures brought about by the work of the Bridge Stress Committee set up by the Department of Scientific and Industrial Research led to the relaxation of these restrictions.

Collett hence designed the "King" class to the maximum dimensions of the original GWR 7 ft ¹⁄₄ in (2,140 mm) broad-gauge engineering used to develop its mainline, resulting in the largest loading gauge of all the pre-nationalisation railways in the UK, with a maximum height allowance of 13 feet 5 inches (4.09 m). Consequently, this restricted the "King"s as to where they could operate under both GWR and British Railways ownership. To accommodate the largest possible boiler, the "King" class were equipped with smaller 6 ft 6 in (1.981 m) main driving wheels than the "Castle" class, with boiler pressure raised to a maximum of 250 pounds per square inch (1.72 MPa). This resulted in both the GWR's highest-powered locomotive design, but most importantly a higher tractive effort than the "Castle". This combination allowed the "King" class to pull the now required higher-weight 13+ coach express trains from London to Bristol and onwards to the West Country, at a higher-speed timetable average than the "Castle".

Naming

It was originally intended that the class be named after notable cathedrals, but, in light of an invitation to feature 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.

Operations

The first, No. 6000 King George V, appeared in 1927. After six months of operations, it was shipped to North America for the Centenary celebrations of the B&O, where its sleek appearance and smooth performance impressed all who witnessed it. 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. King George V was presented with a brass bell to mark the occasion.

At the time of being out-shipped from the workshops at Swindon, to fully provide Pole's requested tractive effort target, the "Kings" has enlarged cylinders to 16 ¹⁄₄-inch (412.8 mm) bore, resulting in a tractive effort as out-shopped of 40,300 lbf (179.3 kN). To accommodate this enlarged inner-cylinder combination, the result was the distinctive design of the leading bogie, with outside bearings on the fore wheel and inside bearings on the rear wheel. However, operational experience showed that clearance of the cylinders was problematic, resulting in the replacement of the outer pair on each locomotive's first major overhaul, which resulted in a reduction of tractive effort to 39,700 lbf (176.6 kN).

They were engines to be reckoned with, powering the GWR's crack expresses like the Cornish Riviera Limited up until the end of regular steam hauled express services on the Western Region of British Railways. However, although the GWR claimed that the class was built in response to longer and heavier trains, it was several years after its introduction before the platforms at the GWR's major stations were lengthened to accommodate these trains.

Due to their size and weight, the class was restricted to the London-Taunton-Plymouth (via both Bristol and Westbury) and London-Birmingham-Wolverhampton (via Bicester) main lines, and even then, only after bridge strengthening had taken place, due to the engines' large boilers giving them a high axle weight of 22.5 long tons (22.9 t). The "Kings" were unable to serve Cornwall, due to the Royal Albert Bridge being too weak for their weight, and so when they were hauling the Cornish Riviera Limited, they had to be swapped for a 'Castle' or 'Hall' at Devonport. Swindon-born and trained William Stanier based his LMS Princess Royal Class design on the King Class, but with an enlarged boiler and firebox necessitating a 4-6-2 wheel arrangement.

British Rail

In 1947 experiments had been made with a four-row high-degree superheater in No. 6022 King Edward III, owing to a decline in the availability of high-calorific South Wales steam coal, on which the GWR had always relied for its good locomotive performance. During the 1948 locomotive exchanges, King Henry VI had 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. After this, four-row superheaters were fitted to the 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.

They were all withdrawn in 1962, replaced by the western region's short lived diesel Hydraulic Western Class locomotives.

Accidents and incidents

List of King Class locomotives

Thirty-one locomotives were built at Swindon, as follows:

Of the 31, only 30 were in service simultaneously. The original 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 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.

Preservation

As a result of its previous 7 ft ¹⁄₄ in (2,140 mm) 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 feet 5 inches (4.09 m). Consequently, this restricted them as to where they could operate under both GWR and British Railways ownership.

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 feet 1 inch (3.99 m).

Two of the three preserved Kings (6000 King George V and 6024 King Edward I) have operated on the main line in preservation.

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 inches (102 mm) 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.