Editing GWR 4073 Class (section)

==Production==
Unlike the Star class, there was no prototype. Collett was sufficiently confident of the design to place an order with [[Swindon Works]] (Lot 224) for ten locomotives in 1923, although there was a four-month delay between the appearance of the first example in August 1923 and the second in December, to allow for the correction of any teething problems.{{sfnb |le Fleming|1953 |p=H17}} Thereafter the remaining eight locomotives came out at regular intervals until April 1924. They were 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. The new locomotives were named after castles, also in the west, beginning with ''[[GWR 4073 Class 4073 Caerphilly Castle|Caerphilly Castle]]''.

Over the twenty-seven years from August 1923 to August 1950, 155 Castles were built new at Swindon Works and a further sixteen were converted from other classes. In February 1952, two engines, 4082 ''Windsor Castle'' and 7013 ''Bristol Castle'', swapped names and numbers: 7013 was disguised as 4082 to run [[George VI]]'s funeral train and the numbers were never swapped back. 4082 was withdrawn from service in 1964 as 7013 and 7013 was withdrawn from service as 4082 in 1965.

===New builds===
The new-builds were as follows.{{sfnb |le Fleming|1953 |p=H17–H18}}

Great Western Railway
*Lot 224: Nos. 4073–4082, delivered August 1923 to April 1924.
*Lot 232: Nos. 4083–4092, delivered May to August 1925.
*Lot 234: Nos. 4093–4099 and 5000 to 5012, delivered May 1926 to July 1927.
*Lot 280: Nos. 5013–5022, delivered June to August 1932.
*Lot 295: Nos. 5023–5032, delivered June to August 1932.
*Lot 296: Nos. 5033–5042, delivered May to July 1933.
*Lot 303: Nos. 5043–5067, delivered March 1936 to July 1937. (Nos. 5043–5063 were originally named after Castles, but were renamed in 1937 after Earls)
*Lot 310: Nos. 5068–5082 delivered June 1938 to June 1939. (Nos. 5069 and 5070 were named after [[Isambard Kingdom Brunel]] and [[Daniel Gooch|Sir Daniel Gooch]]; In 1941 5071–5082 were renamed after aircraft used by the [[Royal Air Force]])
*Lot 324: Nos. 5093–5097, delivered June to July 1939.
*Lot 357: Nos. 5098–5099, 7000–7007 delivered May to July 1946.

[[Western Region of British Railways|British Railways (Western Region)]]
*Lot 367: Nos. 7008–7027, delivered May 1948 to August 1949.
*Lot 375: Nos. 7028–7037, delivered May 1950 to August 1950.
These locomotives were built with minimal changes to the dimensions. However, 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.<ref name=KCGWR/> Those built before 1926 were fitted with a {{convert|3500|impgal|abbr=on}} tender but thereafter {{convert|4000|impgal|abbr=on}} became standard for the class.

===Rebuilds===
Between January and September 1924, the only Great Western [[4-6-2]], No.111 [[GWR 111 The Great Bear|The Great Bear]], was rebuilt into a member of the Castle Class, although only the "front portion of the original [[Locomotive frame|frames]] and the number plates were used again but probably little else". The new locomotive was renamed ''Viscount Churchill'' and survived until withdrawal in July 1953.{{sfnb |le Fleming|1953 |p=H13}}

In April 1925, Star class No. 4009 ''Shooting Star'' was likewise rebuilt as a Castle by extending the frames and fitting a new Castle Class boiler and cab. It was renumbered and renamed 100 A1 ''Lloyds'' and was withdrawn in 1950.{{sfnb |le Fleming|1953 |p=H17–H19}}

In October 1925 a second Star class, No. 4016 ''The Somerset Light Infantry (Prince Albert's)'', was similarly converted to a Castle although in this case, it retained its name and number.{{sfnb |le Fleming|1953 |p=H13}} Two further conversions of Stars were undertaken in 1926; Nos. 4032 ''Queen Alexandra'' and 4037 ''The South Wales Borderers'' retaining their names and numbers and surviving until 1951 and 1962 respectively.

In November 1929 the prototype for the Star Class, No. 4000 ''North Star'' was rebuilt into a Castle, being subsequently withdrawn in 1957.

Between 1937 and 1940 a further ten members of the 'Abbey series' of the Star class (Nos. 4063–4072) were rebuilt as Castles on Lot 317. They were allocated new numbers 5083 to 5092 but retained their original names and were withdrawn between 1958 and 1964.