Castle-class corvette

In mid-1939, the Admiralty ordered 175 Flower-class corvettes for protecting shipping on the east coast of Britain. They were designed to be built in large numbers in small shipyards without propulsion and other components (mainly gearboxes, but also guns) then in short supply so not compete with other warships for construction. By the time the Flowers began entering service in late-1940, due to their long range they were required to undertake missions beyond coastal waters.Friedman (2006): page 134Friedman (2006): page 135 The Flowers were unsuited for open-ocean escort missions in the North Atlantic, especially in poor weather; they lacked speed, endurance, and habitabilityFriedman (2006): page 136 but became the mainstay of the Mid-Ocean Escort Force protecting convoys crossing the Atlantic.

The Royal Navy recognized the limitations of the Flower and began designing an open-ocean escort in November 1940,Friedman (2006): page 139 which became the {{sclass2|River|frigate}}.Friedman (2006): page 140 The larger Rivers were too expensive to produce at the required rate and needed larger slipways. In response, the {{sclass2|Loch|frigate}} was developed in late-1942, which was developed from the River and designed for prefabricated construction.Friedman (2006): page 149 The Castle was developed from a proposal by Smith's Dock Company – who had designed the Flower-class – for a stretched Flower.Brown (2007): chapter 7, "The origin of the Castles has been mentioned previously..." The result was a scaled-down version of the Loch for shipyardsFriedman (2006): page 156 that only built corvettes using mainly traditional methods.

The design was approved in May 1943 and 96 Castles were ordered from yards in the UK and Canada. Fifteen British and all 37 Canadian ships were later cancelled; Canada receiving twelve British-built ships instead. The UK completed a further five as convoy rescue ships for its Merchant Navy. Four became weather ships after the war.

The Castle resembled later Flowers with an extended forecastle and mast behind the bridge, but was 135 tons heavier and 47 feet longer. The Admiralty Experiment Works at Haslar developed an improved hull form which, in combination with the increased length, made the Castle at least half a knot faster than the Flower despite using the same engine. The Castle also had a single-screw.Brown (2007): chapter 7, "It was thought that at least 200 new escorts..." A lattice mainmast was used instead of the pole version fitted to the Flowers.

Construction used mainly traditional methods with as much welding as possible. Scantling was based on the Flower, but lightened in some areas. The wireless office (the same as on the Loch), the radar office, and the lattice mast were installed as prefabricated units.

The Castle was armed with a Squid anti-submarine mortar, directed by Type 145 and 147B ASDIC. The Flower used the older Hedgehog mortar and could not be fitted with Squid.Friedman (2006): page 146 The first operational Type 147 and Squid were installed aboard HMS Hadleigh Castle in September 1943.Brown (2007): chapter 7, "The first operational set was installed..."

In place of the BL 4-inch Mk IX main gun, the Castles had the new QF 4-inch Mk XIX gun on a High-Angle/Low-Angle mounting which could be used against aircraft as well as surface targets such as submarines.

The Castle was criticized for being barely fast enough to fight German Type VII submarines and difficult to handle at low speed.

The following vessels were all originally built for the Royal Navy, but were transferred to the RCN on completion (for details of builders and construction dates see under Royal Navy below). All their pennant numbers (except Hedingham Castle, which was never completed), as well as their names, were changed when transferred.

• HMCS Arnprior (K494) (ex-{{HMS|Rising Castle|K398|6}})
• HMCS Bowmanville (K493) (ex-{{HMS|Nunney Castle|K446|6}}), sold to Republic of China as cargo ship, but taken over by the Communist People's Liberation Army Navy after the end of the Chinese Civil War and rearmed with Soviet guns, entering PLAN service as Guangzhou.
• HMCS Copper Cliff (K495) (ex-{{HMS|Hever Castle|K521|6}})
• HMCS Hespeler (K489) (ex-{{HMS|Guildford Castle|K378|6}}) (later SS Chilcotin)
• HMCS Humberstone (K497) (ex-{{HMS|Norham Castle|K447|6}})
• HMCS Huntsville (K499) (ex-{{HMS|Woolvesey Castle|K461|6}})
• HMCS Kincardine (K490) (ex-{{HMS|Tamworth Castle|K393|6}})
• HMCS Leaside (K492) (ex-{{HMS|Walmer Castle|K405|6}}, later SS Coquitlam II)
• HMCS Orangeville (K491) (ex-{{HMS|Hedingham Castle|K491|6}}), sold to Republic of China as cargo ship, but taken over by the ROC Navy on 29 June 1950 and rearmed with US guns, entering ROCN service as De An (德安)
• HMCS Petrolia (K498) (ex-{{HMS|Sherborne Castle|K453|6}})
• HMCS St. Thomas (K488) (ex-{{HMS|Sandgate Castle|K473|6}}, later SS Camosun III)
• HMCS Tillsonburg (K496) (ex-{{HMS|Pembroke Castle|K450|6}}), sold to Republic of China as cargo ship, but taken over by ROCN on 29 June 1950 and rearmed with US guns, entering ROCN service as Kao An (高安)

The first of the Castle-class were the prototypes Hadleigh Castle and Kenilworth Castle, ordered on 9 December 1942; another 12 vessels were also ordered on 9 December, also under the 1942 War Programme. The remaining eighty-one ships were all ordered for the RN under the 1943 War Programme, of which thirty were completed. Fifty-one of these ships (15 from UK shipyards and 36 from Canadian shipyards) were cancelled late in 1943.

Notes: (a) from the previous order placed for a Modified Flower-class corvette named Amaryllis.

Two of those ordered 3 March 1943, three ordered 4 May 1943 and two ordered 10 July 1943 were all cancelled, as were all thirty-six ordered from Canadian shipyards on 15 March 1943.

• {{HNoMS|Tunsberg Castle}} – HMS Shrewsbury Castle was loaned to the Royal Norwegian navy on 17 April 1944. On 12 December 1944, she hit a mine and sank.

Fifteen ships ordered for the Royal Navy from UK shipyards as part of the 1943 Programme were all cancelled on 31 October 1943:

• Caldecot Castle – ordered 19 January 1943 from John Brown & Company, Clydebank.
• Dover Castle – ordered 19 January 1943 from A. & J. Inglis, Glasgow.
• Dudley Castle – ordered 19 January 1943 from A. & J. Inglis, Glasgow.
• Bere Castle – ordered 23 January 1943 from John Brown & Company, Clydebank.
• Calshot Castle – ordered 23 January 1943 from John Brown & Company, Clydebank.
• Monmouth Castle (originally to have been Peel Castle) – ordered 23 January 1943 from John Lewis & Sons, Aberdeen.
• Rhuddlan Castle – ordered 23 January 1943 from John Crown & Sons, Sunderland.
• Thornbury Castle – ordered 23 January 1943 from Ferguson Brothers, Port Glasgow.
• Appleby Castle – ordered 3 March 1943 from Austin, at Sunderland.
• Tonbridge Castle – ordered 3 March 1943 from Austin, at Sunderland.
• Norwich Castle – ordered 4 May 1943 from John Brown & Company, Clydebank.
• Oswestry Castle – ordered 4 May 1943 from John Crown & Sons, Sunderland.
• Pendennis Castle – ordered 4 May 1943 from John Crown & Sons, Sunderland.
• Alton Castle – ordered 10 July 1943 from Fleming & Ferguson, Paisley.
• Warkworth Castle – ordered 10 July 1943 from Fleming & Ferguson, Paisley.

The following ships were ordered on 15 March 1943 for the Royal Navy from Canadian shipyards for completion between May 1944 and June 1945, but were all cancelled in December 1943:

{{div col|colwidth=10em}}

• Aydon Castle
• Barnwell Castle
• Beeston Castle
• Bodiam Castle
• Bolton Castle
• Bowes Castle
• Bramber Castle
• Bridgnorth Castle
• Brough Castle
• Canterbury Castle
• Carew Castle
• Chepstow Castle
• Chester Castle
• Christchurch Castle
• Clare Castle
• Clavering Castle
• Clitheroe Castle
• Clun Castle
• Colchester Castle
• Corfe Castle
• Cornet Castle
• Cowes Castle
• Cowling Castle
• Criccieth Castle
• Cromer Castle
• Devizes Castle
• Dhyfe Castle
• Dunster Castle
• Egremont Castle
• Fotheringay Castle
• Helmsley Castle
• Malling Castle
• Malmesbury Castle
• Raby Castle
• Trematon Castle
• Tutbury Castle
• Wigmore Castle

{{Div col end}}

• {{HMS|Hurst Castle|K416|2}} was sunk by {{ship|German submarine|U-482||2}} northwest of Ireland on 1 September 1944.
• HNoMS Tunsberg Castle was sunk by a mine near Båtsfjord, Norway on 12 December 1944.
• {{HMS|Denbigh Castle|K696|2}} was hit by a torpedo from {{ship|German submarine|U-992||2}} in the Barents Sea on 13 February 1945. She was towed by {{HMS|Bluebell|K80|2}} to the Kola Inlet but later capsized.

• {{ship|German submarine|U-744||2}} was sunk by {{HMS|Icarus|D03|2}}, {{HMCS|St. Catharines|K325|2}}, {{HMCS|Fennel|K194|2}}, {{HMCS|Chilliwack|K131|2}}, {{HMCS|Chaudiere|H99|2}}, {{HMCS|Gatineau|H61|2}} and {{HMS|Kenilworth Castle|K420|2}} on 6 March 1944
• {{ship|German submarine|U-484||2}} was sunk in the north-west of Ireland by {{HMS|Portchester Castle|K362|2}} and {{HMS|Helmsdale|K253|2}} on 9 September 1944
• {{ship|German submarine|U-1200||2}} was sunk south of Ireland by {{HMS|Pevensey Castle|K449|2}}, {{HMS|Lancaster Castle|K691|2}}, {{HMS|Portchester Castle|K362|2}} and {{HMS|Kenilworth Castle|K420|2}} on 11 November 1944
• {{ship|German submarine|U-387||2}} was sunk in the Barents Sea by {{HMS|Bamborough Castle|K412|2}} on 9 December 1944
• {{ship|German submarine|U-877||2}} was sunk north-west of the Azores by {{HMCS|St. Thomas|K488|2}} on 27 December 1944
• {{ship|German submarine|U-425||2}} was sunk in the Barents Sea by {{HMS|Lark|U11|2}} and {{HMS|Alnwick Castle|K405|2}} on 17 February 1945
• {{ship|German submarine|U-878||2}} was sunk in the Bay of Biscay by {{HMS|Vanquisher|D54|2}} and {{HMS|Tintagel Castle|K399|2}} on 10 April 1945

The final third of the film The Cruel Sea is set on the Castle-class corvette Saltash Castle (portrayed by {{HMS|Portchester Castle|K362|2}}).

Three were converted to passenger/cargo ships for the Union Steamship Company of British Columbia and were known as the White Boats.Twigg They were operated from 1946 to 1958 but were heavy on fuel and had limited cargo capacity, for example they could not carry cars in the hold.

• SS Camosun III – ex-HMCS St. Thomas, HMS Sandgate Castle
• SS Chilcotin – ex-HMCS Hespeler, HMS Guildford Castle
• SS Coquitlam II – ex-HMCS Leaside, HMS Walmer Castle

{{Reflist}}

• {{Cite book |last=Brown |first=David K. |title=Atlantic Escorts : Ships, Weapons & Tactics in World War II |date=2007 |publisher=Seaforth Publishing |isbn=978-1-78346-901-7 |location=Barnsley, UK|author-link=David K. Brown}}
• {{cite book|last=Friedman|first=Norman|title=British Destroyers & Frigates: The Second World War and After|year=2008|publisher=Seaforth Publishing|location=Barnsley, UK|isbn=978-1-84832-015-4 |author-link=Norman Friedman}}
• {{cite book|last=Lenton|first=H. T.|title=British & Empire Warships of the Second World War |publisher=Naval Institute Press|location=Annapolis, Maryland|year=1998 |isbn=1-55750-048-7 |author-link=Henry Trevor Lenton}}
• Twigg, Arthur M.: Union Steamships Remembered: 1920–1958 (1997) {{ISBN|1-55056-516-8}}.

{{Commons category|Castle class corvettes}}

• [http://www.castlecorvette.co.uk/ Castle-class corvette (Frigate) Association]
• [http://www.uboat.net/allies/warships/class.html?ID=4 Castle-class corvettes on U-Boat.net]

{{Castle class corvette}}

{{WWII British ships}}

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Category:Corvette classes