Power Classification	6P reclassified 7P in 1951
Introduced	1923- 1950
Designer	Collett
Company	GWR
Weight – Loco	79t 17cwt
Tender	46t 14cwt
Driving Wheels	6ft 8.5ins
Boiler Pressure	225psi superheated
Cylinders	Four– 16in x 26in
Tractive Effort	31,625lbf
Valve Gear	Inside Walschaert with rocking shafts (piston valve)

Collett’s four-cylinder Castle class was a development of Churhward’s 4000 Star class with increased dimensions (5083 to 5092 were rebuilds of the Abbey series of Star class locomotives). In fact the first working drawings used to construct Castle class locomotives were Star class plans with alterations made in red ink. Several were rebuilt from Star class locomotives. When introduced they were heralded as Britain’s most powerful express passenger locomotive, being some 10% more powerful than the Stars.

Number in Service.

	Built		Withdrawals	No. in Service
	BR Numbers	Quantity
New Builds
1923	4073-4074	2		2
1924	4075-4082	8		10
1925	4083-4092	10		20
1926	4093-4099 & 5000-5002	10		30
1927	5003-5012	10		40
1932	5013-5022	10		50
1934	5023-5032	10		60
1935	5033-5042	10		70
1936	5043-5057	15		85
1937	5058-5067	10		95
1938	5068-5077	10		105
1939	5078-5082 & 5093-5097	10		115
1946	5098-5099 & 7000-7007	10		125
1948	7008-7017	10		135
1949	7018-7027	10		145
1950	7028-7037	10		155
Rebuilt from Star and Great Bear
1906	4000	1
1907	100A1	1
1908	111	1
1908	4016	1
1910	4032, 4037	2
1922	5083-5086	4
1923	5087-5092	6		16
Total Built				171
1950	100A1		1	170
1951	4016 & 4016		2	168
1952				168
1953	111		1	167
1954				167
1955				167
1956				167
1957	4000		1	166
1958	5086		1	165
1959	4091, 5010 & 5083		3	162
1960			7	155
1961			3	152
1962			55	97
1963			48	49
1964			37	12
1965			12	0

• 100A1 was built as Star class 4009 in 1907 but rebuilt as a Castle in 1936 and renumbered 100A1. It was withdrawn from service in 1950.
• 111 was rebuilt from the Great Bear GWR Pacific built in 1908. It was withdrawn from service in 1953.
• 4016 was built as a Star class in 1908 but rebuilt as a Castle in 1925. It was withdrawn from service in 1951.
• 4032 and 4037 were built as Star class engines in 1910 and rebuilt as Castle class locomotives in 1926
• 5083-92 were the last ten Star class locomotives built and were known as Abbeys. They were rebuilt as Castle class locomotives and renumbered 4063-4072 between 1937 and 1940.
• Of the twelve withdrawn in 1965 nine were from the batches built by BR in 1948 to 1950. The other three being built in 1932, 1933 and 1936. The twelve had been based at Oxley (5), Tyseley (3) and Gloucester (4) when withdrawn from service.

The first, 4073 Caerphilly Castle, made its debut at Paddington station on 23 August 1923.

They were one of the most successful locomotive classes ever built in this country (with a total of 171 being constructed), and they greatly influenced locomotive design on the other three main Railway Companies. The 6000 King class locomotives were directly developed from these engines and were very similar in appearance, although slightly larger.

It is interesting to note that whilst some of the Castle class locomotives have been recorded achieving very fine performances but the well known railway author O S Nock who timed very many said that he did not know of a large class of locomotives where the performance varied so much between engines. It is noticeable that many of the best performances were recorded with the same few locomotives. There were those who said the Star class were better engines and that the Castle design had been hurried in order to compete with the Gresley Pacifics.

4073 was exhibited at the British Empire Exibition at Wembley in 1924 where it was positioned next to 4472 Flying Scotsman which led to trials to compare the locomotives. These trials commenced in April 1925 with 4079 Pendennis Castle representing the GWR on the Great Northern main line and A3 class, 4474 Victor Wild, representing the LNER on Great Western tracks. On the first morning Pendennis Castle was to work a 480 ton train from Kings Cross to Doncaster, and LNER officials fully expected the smaller, lighter engine to encounter problems climbing Holloway Bank. However railway writer Cecil J Allen records that the GWR locomotive made a faster start from King’s Cross to Finsbury Park than any A3 class LNER pacific he had recorded up to that time and over the trial Pendennis Castle kept well within the scheduled time and used less coal, considerably denting LNER pride. For the LNER, Victor Wild was compared on the Cornish Riviera Express to 4074 Caldicot Castle and although it kept to time the longer wheelbase of the pacific proved unsuited to the many curves on the route. Again the GWR took the honours with Caldicot Castle burning less fuel and always ahead of time, this being illustrated on the last 2 days of the trial by gaining 15 minutes on the schedule in both directions. The LNER A3 pacifics were altered to take into account the lessons learned.

Much was made in GWR publicity of the roomy cab with side window with which the Castle class were equipped. The GWR panache was provided by restoration for the first time after World War 1 of the copper-capped chimney and polished brass safety-valve cover. The tender attached to the class as originally built was the standard lo-sided tender taking six tons of coal and 3,500 gallons of water. The Castles average coal consumption was one of the lowest in the country (2.83 pounds per drawbar horsepower per hour compared to 4 pounds consumption figure common for the other railways in the 1920s), but the standard tender was changed for a 4,000 gallon design that emerged in 1926.

5005 was partially streamlined in 1935. The streamling was removed in sections from 1937 to 1947.

There was lots of name changing within the class.  4082 Windsor Castle and 7013 Bristol Castle swapped identities in February 1952. The original 4082 had once been driven by King George V on a visit to Swindon. It was felt that 4082 would be a suitable locomotive to haul the late King George V1’s funeral train in 1952 from London to Windsor. Unfortunately, the locomotive was undergoing repairs in Swindon at the time and could not be made ready in time. Therefore 7013 took its name and number and the two locomotives kept their new identities.

It is interesting to note that the Castle class was the second class of locomotives to be named after castles. Earlier, in 1900, the Highland Railway had introduced the first six engines of the Castle class built for that railway. They were named after the residencies of the directors of the Highland Railway who all lived in castles.

Amongst the other changes was 7007 which was renamed Great Western as it was the last passenger express steam locomotive to be built by the GWR.

In 1946 Hawksworth, Collett’s successor, introduced a higher degree of superheat to the Castle boiler with resulting increased economy in water consumption. From 1956 the fitting of double chimneys to selected engines, combined with larger superheaters, further enhanced their capacity for sustained high-speed performance. In 1958 7018 Drysllwyn Castle, fitted with a double chimney and a four-row superheater, hauled ‘The Bristolian’ express at 100 mph at Little Somerford. The Castle class was noted for superb performance overall, and notably on the Cheltenham Flyer during the 1930s: for example, on 6 June 1932 the train, pulled by 5006 Tregenna Castle, covered the 77.25 miles from Swindon to Paddington in 56 minutes 47 seconds at an average speed of 81.68 mph start-to-stop. This world record for steam traction was widely regarded as an astonishing feat but it is worth noting that this was a staged run organised by the GWR and the load behind the Castle was only 186 tons which was 34 tons less than its normal lightest load. The speeding up of the Cheltenham Flyer was one of the last act made by Sir Felix Pole before he retired as GWR General Manager in 1929. From July train was scheduled to cover the 77.3 miles between Swindon and Paddington in 70 minutes making it the world’s fastest train. It was usually hauled by a Castle class engine but the load was generally no more than 250 tons which was a relatively light load. It is interesting to note that one factors which influenced the GWR to introduce the fast times for the Cheltenham Flyer was that the record that the GWR had had for the length of its non-stop run of nearly 226miles from Paddindton to Plymouth had been eclipsed by the LNER (Kings Cross to Edinburgh – 393 miles) and LMSR (Euston to Carlisle – 299 miles). The Cheltenham Flyer utilised a slightly downhill and well aligned track from Swindon to Paddington and ran at a quiet time of day. The GWR also had a special signalling arrangement for the train which was designed to ensure that long sections were guaranteed to be completed without any restrictions from other trains.

In June 1937 5039 Rhuddlan Castle hauled the Cheltenham Flyer and covered the journey from Swindon to Paddington slightly slower than that of 5006 Tregenna Castle in June 1932. The later run however was eased from Southall into Paddington otherwise it would have at least matched the earlier timings. 5039 attained a speed of 95 mph on 1937 train and averaged 89.3 mph for the 57.4 miles between Uffington and Southall.

111 was rebuilt from GWR pacific The Great Bear of the same number. It was the first pacific type in Britain and when built in 1908 it was the most powerful express engine in the country. Because of its weight it was restricted to main line use between London and Bristol. This restricted its usefulness and it was rebuilt as a Castle class in 1924 and named Viscount Churchill.

The first years of the nationalised Western Region of British Railways saw Castle production continue at the rate of 10 per year until the last Castle, 7037 Swindon was completed in August 1950 making a total of 171 Castle Class locomotives.

The lowest mileage of a Castle was the 580,346 miles run by 7035 Ogmore Castle between August 1950 and June 1964, the highest mileage of any true Castle class was run by 4080 Powderham Castle which totalled 1,974,461 miles in 40 years and 5 months. The highest mileage run of any GWR engine was 4037 South wales Borderers which was rebuilt from Star class Queen Philippa. This engine is credited with covering 2,429,722 miles over a total of 51 years and 8 months until it was withdrawn as the final Star class locomotive in September 1962 and sold for scrap to Cashmore’s at Newport.

An important improvement was made starting with the batch of locomotives from 5023 Brecon Castle onwards. At Swindon and in common with many other railways companies, locomotive alignment between the frames, cylinders and axles box guides was made by using wires, trammels and a centre prop. As the performance and reliability of a locomotive greatly depend on this alignment, the German State Railways began use of Zeiss optical alignment gear and after modification to the Great Western locomotives, it was used for all new builds and locomotive repairs. In addition, due to the exacting dimensions that this achieved, valve gear tolerance could be greatly reduced to the absolute minimum when new, so much so that an ex-Great Western man, when reviewing the manufacturing practices of other railway companies, remarked “We scrap at the amount of clearance that they start with”. Many observers noted that this batch of Castles ran very quietly when new. It is worth noting in this context that 5030 Shirburn Castle completed 420,000 miles before it had its boiler removed from the frames. Dimensions previously maintained to within an accuracy of plus or minus 0.010 in were afterwards made to within plus or minus 0.002 in.

The Castle class were thus built over a period of 27 years (1923-1950) which is longer than for any other class of British express engine.

Castle class locomotives built from number 5033 in 1935 were fitted with speedometers for the first time.

Accidents and Incidents

• On 19th December 1933 4085 Berkeley Castle was hauling the Paddington to Fishguard express when it hit and killed the retired GWR Chief Mechanical Engineer Churchward. Churchward had retired from his role with the GWR in 1922 but he continued to live in a GWR owned house near to the line at Swindon and he continued to take an interest in the railway.
  • As an all-round railwayman he recognised the sound of a “hanging” rail joint near to his house and phoned the Divisional Engineer at Bristol and urged him to do something about it. After a few days passed taken and with no action and the noise getting worse Churchward told his housekeeper one foggy morning that he was going out “to find out where that damned joint is”. These were to be the last words he spoke as he searched for the fault in the foggy conditions he appears not to have heard the sound of the approaching 8:55am from Paddington and he was knocked down and killed. By this time Churchward was aged 76 and had poor eyesight and was hard of hearing.
  • The locomotive was built three years after he retired as CME but was a development of his Star class.

• On 2^nd July 1941 locomotive 4091 Dudley Castle was involved in a collision with LMS 8F 8293 near Slough which resulted in the death of five passengers on the Plymouth to Paddington train which the Castle class locomotive was hauling. 4091 was the first real Castle to be taken out of service in January 1959 when based at Old Oak Common. The 8F needed repairs and thus missed being shipped to mainland Europe and it survived with BR until the end of steam in June 1968.

• On 30th November 1948 5022 Wigmore Castle was hauling a Paddington to Birkenhead passenger train when it ran past a danger signal in poor visibility and ran into 5101 class 4150 at Lapworth. There were no serious injuries although the tank engine required its front end to be rebuilt.

• On 20 August 1957 7002 Devizes Castle was hauling a ten coach express passenger train from the West Country to Paddington. Shortly after sighting the Slough West distant signal was set at caution the driver closed the regulator. Just sfter he had done that he slumped down onto the footplate and struck his head on the water scoop handle as he fell. The fireman hauled him up against the cab side but with the train passing a distant signal at caution and stioll travelling at speed the safety of the train had to take priority. The fireman (Ron Giles)had come on duty as a relief fireman and he had no previous experience of working on a express passenger train – he had only had on previous working to London. The fireman managed to bring the train to a hault and it was fortunate that there was another crew on the train who could take over. The driver was later taken off the train but he was dead.

• On 12 November 1958, a freight train overran signals and was derailed at Highworth Junction, Swindon. Locomotive 5009Shrewsbury Castle was hauling a newspaper train which collided with the wreckage.

Preservation

Of the 8 Castle’s to be preserved 5 have operated on the mainline: 5029 Nunney Castle, 5043 Earl of Mount Edgcumbe, 5051 Earl Bathurst, 5080 Defiant & 7029 Clun Castle. 4073 Caerphilly Castle was given directly to the national collection upon withdrawal and 7027 Thornbury Castle is currently in ex Barry Scrapyard condition. Although 4079 Pendennis Castle has worked on the mainline in preservation it hasn’t been on British soil as she spent most of itsr preserved years in Australia, at present it is undergoing a mainline overhaul.

• 4073 Caerphilly Castle
• 4079 Pendennis Castle
• 5029 Nunney Castle
• 5043 Earl of Mount Edgcumbe
• 5051 Drysllwyn Castle (Earl Bathhurst)
• 5080 Defiant (Ogmore Castle)
• 7027 Thornbury Castle
• 7029 Clun Castle

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