GWR 4073 Class

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GWR 4073 Castle class
5034 Corfe Castle fresh from the works.jpg
5034 Corfe Castle fresh from Swindon Works, 1954.
Type and origin
Power type Steam
Designer Charles Collett
Builder GWR / BR Swindon Works
Build date 1923–1950
Total produced 171
Configuration 4-6-0
UIC classification 2'C h4
Gauge 4 ft 8 12 in (1,435 mm)
Leading wheel
3 ft 2 in (0.965 m)
Driver diameter 6 ft 8 12 in (2.045 m)
Minimum curve 8 chains (530 ft; 160 m) normal,
7 chains (460 ft; 140 m) slow
Length 65 ft 2 in (19.86 m) over buffers
Width 8 ft 11 in (2.72 m)
Height 13 ft 4 12 in (4.08 m)
Axle load 19 long tons 14 cwt (44,100 lb or 20 t) full
Weight on drivers 58 long tons 17 cwt (131,800 lb or 59.8 t) full
Locomotive weight 79 long tons 17 cwt (178,900 lb or 81.1 t) full
Tender weight 47 long tons 6 cwt (106,000 lb or 48.1 t) full
Fuel type Coal
Fuel capacity 6 long tons 0 cwt (13,400 lb or 6.1 t)
Water capacity 4,000 imp gal (18,000 l; 4,800 US gal)
Boiler pressure 225 lbf/in2 (1.55 MPa)
Firegrate area 29.36 sq ft (2.728 m2)
Heating surface:
– Tubes
1,857.7 sq ft (172.59 m2) (Collett)
1,799.5 sq ft (167.18 m2) (Hawksworth)
– Firebox 162.7 sq ft (15.12 m2) (Collett)
163.5 sq ft (15.19 m2) (Hawksworth)
Superheater type 14-element "Swindon" (Collett)
21-element (Hawksworth)
Superheater area 262.6 sq ft (24.40 m2) (Collett)
295.0 sq ft (27.41 m2) (Hawksworth)
Cylinders Four (two inside, two outside)
Cylinder size 16 in × 26 in (406 mm × 660 mm)
Valve gear Inside cylinders: Walschaerts
Outside cylinders: derived from inside cylinders via rocking bars.
Valve type Piston valves
Performance figures
Tractive effort 31,625 lbf (140.68 kN)
Operator(s) Great Western Railway
British Railways
Power class GWR: D
BR: 7P
Number(s) 4073–4099; 5000–5099; 7000–7037.
Axle load class GWR: Red
Withdrawn May 1950 to December 1965
Disposition Eight preserved, remainder scrapped

The GWR 4073 Class or Castle class locomotives are a group of 171 4-6-0 steam locomotives of the Great Western Railway.[1] They were originally designed by the railway's Chief Mechanical Engineer, Charles Collett, for working the company's express passenger trains.


The origins of this highly successful design date back to the Star Class of 1907 which introduced the basic 4-cylinder 4-6-0 layout with long-travel valves and Belpaire firebox that was to become synonymous with the GWR. The Star class were built to take the top express trains on the GWR with 61 in service by 1914, but after World War 1 there was a need for an improved design of express locomotive, and to meet this need Chief Mechanical Engineer GJ Churchward had in mind an enlarged Star class design with a standard No.7 boiler.[2] However, the combination would have taken the axle load of such a design over the 20 ton limit set by the civil engineers, and in the end nothing came of the idea.


C. B. Collett succeeded Churchward as Chief Mechanical Engineer of the GWR in 1922 and immediately set about meeting the needs for a new locomotive design that would both supplement the Stars and replace them on the heaviest expresses. Collett's solution was to take the basic layout of the Star and add the larger but lighter No.8 boiler, the increased amount of steam that this produced allowing an increase in the cylinder diameter from 15" to 16". Along with an increased grate area, the result was an increase in tractive effort to 31,625 lb, and a locomotive that looked attractive and well proportioned while remaining within the 20 ton axle limit.

The first 10 locomotives were built in 1923, and numbered 4073 - 4082; the number series continuing unbroken from the Star class. The last 12 Star class locomotives, which were built in 1922-23, had been given names of Abbeys in the western area served by the GWR, and the new locomotives were named after castles also in the west.

When introduced they were heralded as Britain’s most powerful express passenger locomotive, being some 10% more powerful than the Stars. The first, No. 4073 Caerphilly Castle, made its debut at Paddington station on 23 August 1923. The choice of 4082 as Windsor Castle proved fortuitous as this locomotive was used to haul the royal train when King George V and Queen Mary visited Swindon Works in 1924, and much publicity was gained when the king was permitted to drive the engine back from the works to the station before the return journey, with the Queen and several high-ranking GWR officers also on the footplate.[3]

Pendennis Castle at Chester
GWR 4079 Pendennis Castle at Chester General station before hauling the return Birkenhead Flyer to Birmingham, 4 March 1967

During 1924 4073 Caerphilly Castle was exhibited at the British Empire Exhibition at Wembley, alongside Sir Nigel Gresley’s Flying Scotsman. The Great Western declared their engine to be more powerful than its bigger LNER rival, and in terms of tractive effort alone they were entitled to do so. As a result of this GWR General Manager Sir Felix Pole proposed to LNER Southern Area General Manager Alexander Wilson that a trial of the two types should take place via an exchange arrangement.[4] The resulting trials commenced in April 1925 with 4079 Pendennis Castle representing the GWR on the Great Northern main line and 4474 Victor Wild representing the LNER on Great Western tracks. On the first morning Pendennis Castle was to work a 480-ton train from King's 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 LNER pacific he had recorded up to that time[4] 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.[4]

Castle class locos 5051 and 5029 climb St Germans bank

In 1926, number 5000 Launceston Castle was loaned to the London, Midland and Scottish Railway where it ran trials between London and Carlisle. The locomotive fulfilled the LMS requirements so well that the latter first requested the GWR to build a batch of Castles for use on the West Coast Main Line, and, failing that, a full set of construction drawings. Both proposals were rejected by the GWR Board of Directors. The LMS eventually succeeded in gaining access to the design by recruiting William Stanier, the GWR's Works Manager at their main Swindon railway works to become the new Chief Mechanical Engineer for the LMS.[5]

Nunney Castle steam special passing through Dorchester West on its return from Weymouth to Bath 14 August 2011

So successful was the Castles' design that construction continued at intervals until 1950, by which time 171 had been built. This included 15 converted from the Star class, plus the rebuilding of The Great Bear, the Great Western’s only Pacific locomotive.

In 1946 Frederick 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 No. 7018 Drysllwyn Castle, fitted with a double chimney and a four-row superheater, hauled ‘The Bristolian’ express at 100 mph at Little Somerford.

Accidents and incidents[edit]

  • On 12 November 1958, a freight train overran signals and was derailed at Highworth Junction, Swindon, Wiltshire. Locomotive No. 5009 Shrewsbury Castle was hauling a newspaper train which collided with the wreckage.[6]


171 Castles were built or converted over a 27-year span from August 1923 to August 1950 occupying the GWR number series: 4073–4099; 5000–5099; 7000–7037; plus 7 odd numbers of converted or rebuilt locos:

  • Batch1: 4073 - 4082[3] were delivered between June 1923 and April 1924.[2]
  • Batch2: 4083 - 4092[3] with deliveries from May to August 1925.[2] Between the first two batches, the only Great Western pacific No.111 The Great Bear was converted to a castle, although only the frames and some ancillary items were retained; the new loco being renamed Viscount Churchill. Also included during the second production batch was the conversion of 4009 Shooting Star, this again being renamed, this time as 100 A1 Lloyds. Following on from the second batch, towards the end on 1925, a second Star class was also converted to a Castle although 4016 The Somerset Light Infantry (Prince Albert's) retained its name.[2]
  • Batch3: 4093-4099 and 5000 to 5012,[3] although deliveries continued at the rate of 10 per year through to the end of 1927, with two further conversions of Stars also being done in 1926; 4032 Queen Alexandra and 4037 The South Wales Borderers.[2]

After this there was a pause in the construction programme, and with the conversion of 4000 North Star in 1929, the decade finished with a total of 46 Castles in service, of which 5 were rebuilt Star Class locomotives and one the rebuild of the Great Western Railway's sole 4-6-2. The next 10 years saw the addition of 85 Castles, with minimal changes to the original design of 1923. From 5013 Abergavenny Castle there was an alteration to the shape of the front-end casing over the inside cylinders, and from 5043 Earl of Mount Edgcumbe a shorter chimney was fitted.[3] This brought the number series up to 5097, although numbers 5083 to 5092 were rebuilds of the "Abbey" series of Star class locomotives.[2]

After World War 2, a batch of 10 more Castles, 5998-9 and 7000-7007 were built in 1946 incorporating a new 4-row superheater, the last of the class built by the GWR. 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 Castles handled all but the heaviest loads, these being entrusted to the 30-strong King Class, themselves a development of the Castles with an even larger boiler and smaller wheels (6'6" diameter) for both increased tractive effort and to allow for loading gauge clearance.

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 at an average speed of 81.68 mph start-to-stop (124.3 km at an average speed of 131.4 km/h). This world record for steam traction was widely regarded as an astonishing feat.[3]

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 Castle class was run by 4080 Powderham Castle which totalled 1,974,461 miles in 40 years and 5 months.


Withdrawal started in the 1950s, with the first 100 A1 Lloyds withdrawn from Old Oak Common in March 1950. The first "new build" Castle, number 4091 Dudley Castle was withdrawn from Old Oak Common, nearly 10 years later in January 1959.

The last three castles to be withdrawn were all allocated to Gloucester shed,[2] with 5042 Winchester Castle and 7022 Hereford Castle withdrawn in June 1965. The last to be withdrawn was Clun Castle in December 1965, which worked the last steam train out of Paddington on 27 November 1965.[7]

List of locomotives[edit]

See List of GWR 4073 Class locomotives


On 4 March 1967, Nos. 7029 Clun Castle and 4079 Pendennis Castle hauled specials from Banbury and Oxford respectively to Chester, to mark the end of through trains between Paddington and Birkenhead. Eight Castles survive in preservation.

Of the eight Castles to be preserved, five have operated on the main line: nos. 5029 Nunney Castle, 5043 Earl of Mount Edgcumbe, 5051 Earl Bathurst, 5080 Defiant and 7029 Clun Castle. No. 4073 Caerphilly Castle was given directly to the National Collection upon withdrawal, and no. 7027 Thornbury Castle is currently in ex-Barry Scrapyard condition. Although no. 4079 has worked on the main line in preservation, this was not on British soil as it spent most of its preserved years in Australia, at present it is undergoing overhaul.

As of 2015, only 5043 has a valid main line certificate as 5029 was recently withdrawn requiring an overhaul, 7029 is due to return to main line traffic in late 2015/early 2016.

Image Number Name Built Renamed Withdrawn Owner Current location Current status
GWR Caerphilly Castle 2 db.jpg
Caerphilly Castle
August 1923
May 1960
National Railway Museum
Swindon Steam Railway Museum
On static display
Dscn4066-pendennis-dark-in-shed crop 1200x600.jpg
Pendennis Castle
February 1924
May 1964
Great Western Society
Didcot Railway Centre
Under mainline standard overhaul
5029 Nunney Castle Didcot old slide.jpg
Nunney Castle
May 1934
December 1963
Jeremy Hosking
Awaiting Overhaul
5043 Earl of Mount Edgcumbe Tyseley (2).jpg
Earl of Mount Edgcumbe
(Barbury Castle)
March 1936
September 1937
December 1963
Birmingham Railway Museum
Tyseley Locomotive Works
Operational, main line certified
DSCN2101-earl-bathurst crop 1200x600.JPG
Earl Bathurst
(Drysllwyn Castle)
May 1936
August 1937
May 1963
Great Western Society
Didcot Railway Centre
On static display
GWR Castle Class 5080 Defiant.jpg
(Ogmore Castle)
May 1939
January 1941
April 1963
Birmingham Railway Museum
Buckinghamshire Railway Centre
On static display
Thornbury Castle GWR.jpg
Thornbury Castle
August 1950
December 1963
Pete Waterman
Crewe Heritage Centre
Stored awaiting restoration
7029 Clun Castle Tyseley.jpg
Clun Castle
May 1950
December 1965
Birmingham Railway Museum
Tyseley Locomotive Works
Undergoing mainline standard overhaul

There is now a Haynes Owner's Workshop Manual available.


Hornby Railways currently manufacture a model of the 4073 in OO gauge. The Hornby Dublo brand, then owned by Meccano Ltd, also built "Bristol Castle" (released 1957) for their three-rail system and "Cardiff Castle" for the two-rail system two years later; Wrenn continued the Hornby Dublo model when they took over the range. Airfix/GMR (and later Dapol) also produced an OO model; Tri-ang released a TT gauge model; and Graham Farish (later Bachmann) released N gauge models. Many different prototype examples have been depicted by the various manufacturers.


  1. ^ Ian Allan, compiler (March 1944). The ABC of Great Western Locomotives. Staines, Middlesex: Ian Allan. p. 21. 
  2. ^ a b c d e f g Waters, Laurence (1991). Steam In Action 'Castles'. Shepperton: Ian Allan. ISBN 0 7110 2006 X. 
  3. ^ a b c d e f Nock, O.S. (1969). Kings & Castles of the G.W.R. (2nd ed.). Shepperton: Ian Allan. ISBN 0 7110 0071 9. 
  4. ^ a b c Allen, Cecil J (1970). Salute to the Great Western. Shepperton: Ian Allan. ISBN 0 7110 0181 2. 
  5. ^ Kenneth J. Cook (1974). Swindon Steam 1921–1951. Staines, Middlesex: Ian Allan. p. 52. 
  6. ^ Trevena, Arthur (1980). Trains in Trouble. Vol. 1. Redruth: Atlantic Books. p. 47. ISBN 0-906899-01-X. 
  7. ^ Riley, R.C. (1966). Great Western Album. Shepperton: Ian Allan. ISBN 0 7110 0073 5. 
  • Brian Haresnape (1978). Collett & Hawksworth Locomotives—A Pictorial History. Ian Allan Ltd. ISBN 0-7110-0869-8. 
  • Whitehurst, Brian (1973). Great Western engines, names, numbers, types, classes: 1940 to preservation. Oxford: Oxford Publishing Company. pp. 36–37, 44–46, 64, 103, 143. ISBN 0-902888-21-8. OCLC 815661. 


External links[edit]