| GWR 4073 Castle class | |
|---|---|
| 5034 Corfe Castle fresh from Swindon Works, 1954. | |
| 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 1⁄2 in (1,435 mm) |
| Leading wheel diameter |
3 ft 2 in (0.965 m) |
| Driver diameter | 6 ft 8 1⁄2 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 1⁄2 in (4.08 m) |
| Axle load | 19 tons 14 cwt (44,100 lb or 20.0 t) full |
| Weight on drivers | 58 tons 17 cwt (131,800 lb or 59.8 t) full |
| Locomotive weight | 79 tons 17 cwt (178,900 lb or 81.1 t) full |
| Tender weight | 47 tons 6 cwt (106,000 lb or 48.1 t) full |
| Fuel type | Coal |
| Fuel capacity | 6 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 |
1,799.5 sq ft (167.18 m2) |
| Heating surface: Firebox |
163.5 sq ft (15.19 m2) |
| Superheater area | 295.0 sq ft (27.41 m2) |
| Cylinders | Four (two inside, two outside) |
| Cylinder size | 16 × 26 in (406 × 660 mm) |
| Valve gear | Inside cylinders: Walschaerts Outside cylinders: derived from inside cylinders via rocking bars. |
| Valve type | Piston valves |
| Tractive effort | 31,625 lbf (140.68 kN) |
| Career | Great Western Railway British Railways |
| Power class | GWR: D BR: 7P |
| Number | 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| Withdrawn | May 1950 to December 1965 |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 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.
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A development of the earlier Star Class, 171 Castles were built, over a 27-year span from August 1923 to August 1950. They were numbered 4073–4099; 5000–5099; 7000–7037.
Although most were built new, 16 locos were rebuilt from older locomotives— 15 Star Class locomotives; and the Great Western Railway's sole 4-6-2 locomotive, number 111 The Great Bear.
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.
The origins of this highly successful design date back to G. J. Churchward’s Star Class of 1907. Stars were 4 cylinder 4-6-0s with long-travel valves and Belpaire fireboxes, and were an immediate success on the GWR’s top-link express duties to the west of England. However, with increasing loads the Stars had little in reserve to maintain the restored pre–World War One timings. C.B. Collett succeeded Churchward as Chief Mechanical Engineer of the GWR in 1922 and immediately faced the task of providing more power with little possibility of increasing axle weight. Thus the Castle class was born. When introduced they were heralded as Britain’s most powerful express passenger locomotive, being some 10% more powerful than the Stars. The Castle class locomotives had a larger boiler and cylinder bores were increased from 15 to 16 inches diameter. The first, No. 4073 Caerphilly Castle, made its debut at Paddington station on August 23, 1923.
During 1924 Caerphilly Castle was exhibited at The British Empire Exhibition, Wembley, alongside Sir Nigel Gresley’s Flying Scotsman. The Great Western engine was declared to be more powerful than its bigger LNER rival. During the subsequent ‘Locomotive Interchange Trials’ between the GWR and LNER No. 4079 Pendennis Castle operated on the East Coast Main line alongside Gresley pacifics; while LNER 4474 Victor Wild was sent to work between Paddington and Plymouth alongside No. 4074 Caldicot Castle. All locomotives acquitted themselves well but the compact Castle class demonstrated their superior fuel and water efficiency. 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.[2]
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.
The Castles handled all but the heaviest loads, these being entrusted to the 30-strong King Class. The Kings were themselves a development of the Castles, with an even larger boiler and slightly smaller wheels for increased tractive effort.
Withdrawal started in the 1950s; the last to be withdrawn was Clun Castle at the end of 1965, which worked the last steam train out of Paddington in 1965. However, with preservation, that was not the end of the story for this long lived and popular class of express locomotives. On 4 March 1967 Clun Castle and No. 4079 Pendennis Castle hauled specials from Banbury and Oxford respectively to Chester, to mark the end of through trains between Paddington and Birkenhead.
See List of GWR 4073 Class locomotives
Eight Castles survive in preservation:
| Number | Image | Name | Owner | Current location | Current status |
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On static display | |
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Under rebuild | |
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Operational, main line certified | |
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(Barbury Castle) |
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Operational, main line certified | |
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(Drysllwyn Castle) |
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On static display | |
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(Ogmore Castle) |
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On static display | |
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Stored awaiting restoration | |
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Under overhaul |
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