Denbigh Castle
Class overview
Name	Castle class
Builders	Smiths Dock (5) Fleming and Ferguson (4) Harland and Wolff (4) William Pickersgill & Sons (3) Blyth Dry Dock (3) Caledon Shipbuilding & Eng. (3) Robbs (3) John Lewis and Sons (3) Swan Hunter (3) A and J Inglis (2) Ailsa Shipbuilding (2) George Brown & Co. (2) John Crown & Sons (2) Ferguson Shipbuilders (2) Barclay Curle (1) Ferguson Brothers (1) SP Austin & Son (1)
Operators	Royal Navy  Royal Canadian Navy  Royal Norwegian Navy  Republic of China Navy  People's Liberation Army Navy
Preceded by	Flower class
Succeeded by	None
Planned	95
Completed	44
Cancelled	51
Lost	3
Retired	41
General characteristics
Type	Corvette
Displacement	1,060long tons (1,077 t)
Length	252 ft (76.8 m)
Beam	37 ft (11.3 m)
Draught	10 ft (3.0 m)
Installed power	2 ×water-tube boilers 2,750 ihp (2,050 kW)
Propulsion	1 screw; 1triple-expansion steam engine
Speed	16.5knots (30.6 km/h; 19.0 mph)
Range	9,500 nmi (17,600 km; 10,900 mi) at 10 knots (19 km/h; 12 mph)
Complement	112
Sensors & processing systems	Type 272 radar Type 144Qsonar Type 147B sonar
Armament	1 × single4 in (102 mm)DP gun 1 ×Squidanti-submarine mortar 1 ×depth charge rail, 15 depth charges 2 × twin20 mm (0.8 in)AA guns Up to 6 × single 20 mm AA guns

TheCastle-class corvette was an ocean going convoy escort developed by theUnited Kingdom during theSecond World War. It was the follow-on to theFlower-classcorvette, and designed to be built in shipyards that were producing the Flowers. The Castle-class was a general improvement over the smaller Flowers which were designed for coastal rather than open ocean use.

The Castle-class corvettes started appearing in service during late 1943.

In mid-1939, theAdmiralty ordered 175 Flower-class corvettes for protecting shipping on the west coast of Britain as well as the Western Approaches. 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.^[1][2] The Flowers were unsuited foropen-ocean escort in theNorth Atlantic, especially inpoor weather; they lacked speed, endurance, and habitability but became the mainstay of theMid-Ocean Escort Force protecting convoys crossing the Atlantic.^[2][3]

The Royal Navy recognized the limitations of the Flower and began designing an open-ocean escort in November 1940, which became theRiver-classfrigate.^[4][5] The larger Rivers were too expensive to produce at the required rate and needed larger slipways. TheLoch-classfrigate was developed in late-1942, which was derived from the River and designed forprefabricated construction.^[6] The Castle was developed from a proposal bySmith's Dock Company – who had designed the Flower-class – for a stretched Flower.^[7] The result was a smaller version of the Loch for shipyards that only built corvettes using mainly traditional methods.^[8]

The design was approved in May 1943 and 96 Castles were ordered from yards in the UK andCanada.^[7] Fifteen British and all 37 Canadian ships were later cancelled; Canada receiving twelve British-built ships instead.^[8][7] The UK completed a further five asconvoy rescue ships for itsMerchant Navy. Four becameweather ships after the war.^[8]

The Castle resembled later Flowers with an extended forecastle and mast behind thebridge, but was 135 tons heavier and 47 feet longer. TheAdmiralty Experiment Works atHaslar 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.^[7] The Castle also had a single-screw.^[9] A lattice mainmast was used instead of the pole version fitted to the Flowers.

Construction used mainly traditional methods with as muchwelding as possible.Scantling was based on the Flower, but lightened in some areas. The wireless office^[7] (the same as on the Loch^[8]), the radar office, and the lattice mast were installed as prefabricated units.^[7]

The Castle was armed with aSquid anti-submarine mortar, directed by Type 145 and 147B ASDIC.^[7] The Flower used the olderHedgehog mortar^[4] and could not be fitted with Squid.^[10] The first operational Type 147 and Squid were installed aboardHMSHadleigh Castle in September 1943.^[11][7]

In place of theBL 4-inch Mk IX main gun, the Castles had the newQF 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 fightGermanType VII submarines and difficult to handle at low speed.^[7]

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 underRoyal Navy below). All their pennant numbers (exceptHedingham Castle, which was never completed), as well as their names, were changed when transferred.

• HMCSArnprior (K494) (ex-HMS Rising Castle)
• HMCSBowmanville (K493) (ex-HMS Nunney Castle), sold toRepublic of China as cargo ship, but taken over by the CommunistPeople's Liberation Army Navy after the end of theChinese Civil War and rearmed with Soviet guns, entering PLAN service asGuangzhou.
• HMCSCopper Cliff (K495) (ex-HMS Hever Castle)
• HMCSHespeler (K489) (ex-HMS Guildford Castle) (later SSChilcotin)
• HMCSHumberstone (K497) (ex-HMS Norham Castle)
• HMCSHuntsville (K499) (ex-HMS Woolvesey Castle)
• HMCSKincardine (K490) (ex-HMS Tamworth Castle)
• HMCSLeaside (K492) (ex-HMS Walmer Castle, later SSCoquitlam II)
• HMCSOrangeville (K491) (ex-HMS Hedingham Castle), sold toRepublic of China as cargo ship, but taken over by theROC Navy on 29 June 1950 and rearmed with US guns, entering ROCN service asDe An (德安)
• HMCSPetrolia (K498) (ex-HMS Sherborne Castle)
• HMCSSt. Thomas (K488) (ex-HMS Sandgate Castle, later SSCamosun III)
• HMCSTillsonburg (K496) (ex-HMS Pembroke Castle), sold toRepublic of China as cargo ship, but taken over byROCN on 29 June 1950 and rearmed with US guns, entering ROCN service asKao An (高安)

The first of the Castle-class were the prototypesHadleigh Castle andKenilworth 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 namedAmaryllis.

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 – HMSShrewsbury 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 beenPeel 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:

• Hurst Castle was sunk byU-482 northwest of Ireland on 1 September 1944.
• HNoMSTunsberg Castle was sunk by a mine nearBåtsfjord,Norway on 12 December 1944.
• Denbigh Castle was hit by a torpedo fromU-992 in theBarents Sea on 13 February 1945. She was towed byBluebell to the Kola Inlet but later capsized.

• U-744 was sunk byIcarus,St. Catharines,Fennel,Chilliwack,Chaudiere,Gatineau andKenilworth Castle on 6 March 1944
• U-484 was sunk in the north-west of Ireland byPortchester Castle andHelmsdale on 9 September 1944
• U-1200 was sunk south of Ireland byPevensey Castle,Lancaster Castle,Portchester Castle andKenilworth Castle on 11 November 1944
• U-387 was sunk in theBarents Sea byBamborough Castle on 9 December 1944
• U-877 was sunk north-west of the Azores bySt. Thomas on 27 December 1944
• U-425 was sunk in theBarents Sea byLark andAlnwick Castle on 17 February 1945
• U-878 was sunk in theBay of Biscay byVanquisher andTintagel Castle on 10 April 1945

The final third of the filmThe Cruel Sea is set on the Castle-class corvetteSaltash Castle (portrayed byPortchester Castle).

Three were converted to passenger/cargo ships for theUnion Steamship Company of British Columbia and were known as theWhite Boats.^[12] 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.

• SSCamosun III – ex-HMCSSt. Thomas, HMSSandgate Castle
• SSChilcotin – ex-HMCSHespeler, HMSGuildford Castle
• SSCoquitlam II – ex-HMCSLeaside, HMSWalmer Castle

• Brown, David K. (2007).Atlantic Escorts : Ships, Weapons & Tactics in World War II. Barnsley, UK: Seaforth Publishing.ISBN 978-1-78346-901-7.
• Friedman, Norman (2008).British Destroyers & Frigates: The Second World War and After. Barnsley, UK: Seaforth Publishing.ISBN 978-1-84832-015-4.
• Lenton, H. T. (1998).British & Empire Warships of the Second World War. Annapolis, Maryland: Naval Institute Press.ISBN 1-55750-048-7.
• Twigg, Arthur M.:Union Steamships Remembered: 1920–1958 (1997)ISBN 1-55056-516-8.

Wikimedia Commons has media related toCastle class corvettes.

• Castle-class corvette (Frigate) Association
• Castle-class corvettes on U-Boat.net

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• Castle-class corvettes

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