The Castle-class corvette was an ocean going convoy escort developed by the United Kingdom during the Second World War. It was the follow-on to the , 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.
Background In mid-1939, the Admiralty 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 to 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 in the North Atlantic, especially in poor weather; they lacked speed, endurance, and habitability but became the mainstay of the Mid-Ocean Escort Force protecting convoys crossing the Atlantic.Friedman (2006): page 136
The Royal Navy recognized the limitations of the Flower and began designing an open-ocean escort in November 1940, which became the .Friedman (2006): page 139Friedman (2006): page 140 The larger Rivers were too expensive to produce at the required rate and needed larger slipways. The was developed in late-1942, which was derived 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 smaller version of the Loch for shipyards that only built corvettes using mainly traditional methods.Friedman (2006): page 156
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.
Design 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.
In service The Castle was criticized for being barely fast enough to fight German Type VII submarines and difficult to handle at low speed.
Ships
Royal Canadian Navy 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-) HMCS Bowmanville (K493) (ex-), 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-) HMCS Hespeler (K489) (ex-) (later SS Chilcotin) HMCS Humberstone (K497) (ex-) HMCS Huntsville (K499) (ex-) HMCS Kincardine (K490) (ex-) HMCS Leaside (K492) (ex-, later SS Coquitlam II) HMCS Orangeville (K491) (ex-), 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-) HMCS St. Thomas (K488) (ex-, later SS Camosun III) HMCS Tillsonburg (K496) (ex-), 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)
Royal Navy 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.
+ Castle-class corvettes of the Royal Navy Name Pennant Hull builder Ordered Laid down Launched Commissioned Paid off Fate K355 Smiths Dock Company 9 Dec 1942 4 Apr 1943 21 Jun 1943 18 Sep 1943 Aug 1946 Scrapped, Jan 1959 K420 Smiths Dock Company 9 Dec 1942 7 May 1943 17 Aug 1943 22 Nov 1943 1948 Scrapped, 20 Jun 1959 K689 Fleming & Ferguson 9 Dec 1942(a) 22 Jul 1943 29 Feb 1944 19 June 1944 1947 Scrapped 1958 K412 John Lewis & Co. Ltd 9 Dec 1942 1 Jul 1943 11 Jan 1944 30 May 1944 1950 Scrapped 22 May 1959 K690 John Lewis & Co. Ltd 9 Dec 1942 26 Aug 1943 22 May 1944 29 September 1944 1947 Scrapped Mar 1956 K696 John Lewis & Co. Ltd 9 Dec 1942 30 Sep 1943 5 Aug 1944 30 December 1944 Declared constructive total loss, 13 Feb 1945 K413 John Crown & Sons Ltd 9 Dec 1942 25 Jun 1943 25 Apr 1944 31 Jan 1945 1947 Scrapped, 31 Oct 1960 K529 John Crown & Sons Ltd 9 Dec 1942 2 Nov 1943 30 Oct 1944 12 May 1945 Aug 1945 Scrapped, Apr 1958 K691 Fleming & Ferguson 9 Dec 1942 10 Sep 1943 14 Apr 1944 15 Sep 1944 1947 Scrapped, 20 Jun 1959 Maiden Castle K443 Fleming & Ferguson 9 Dec 1942 1943 8 Jun 1944 November 1944 Became convoy rescue ship Empire Lifeguard before completion; Scrapped, 22 Jul 1955 (ex-Totnes Castle) K447 A. & J. Inglis 9 Dec 1942 30 Sep 1943 12 Apr 1944 6 Sep 1944 Transferred to Canada as HMCS Humberstone 1944; Sold for mercantile service 1947 K530 A. & J. Inglis 9 Dec 1942 30 Sep 1943 20 Jul 1944 10 Dec 1944 1950 Became the weather ship Weather Reporter 1957 K450 Ferguson Shipbuilders 9 Dec 1942 3 Jun 1943 12 Feb 1944 29 June 1944 Transferred to Canada as HMCS Tillsonburg in 1944; Sold for mercantile service 1947; Sold to Republic of China as Kao An 1952 K695 Ferguson Shipbuilders 9 Dec 1942 1943 12 Jun 1944 Oct 1944 Completed as convoy rescue ship Empire Rest K405 George Brown & Co. 19 Jan 1943 1943 3 Oct 1944 1957 Broken up Dec 1958 K594 George Brown & Co. 1943 3 Oct 1944 completed 1945 as convoy rescue ship Empire Shelter K383 Henry Robb, at Leith 20 Apr 1943 1 Sep 1943 31 Dec 1943 Mar 1956 Broken up 10 Jul 1958 K378 Henry Robb, at Leith 25 May 1943 13 Nov 1943 11 Mar 1944 to Canada as HMCS Hespeler, 1944; Sold for mercantile service 1946 (later SS Chilcotin) K491 Henry Robb, at Leith 23 Jul 1943 26 Jan 1944 10 May 1944 to Canada as HMCS Orangeville, 1944; Sold for mercantile service 1947; to Republic of China Navy 1951 as Te An K389 Blyth Dry Dock 22 Apr 1943 1 Sep 1943 5 April 1944 1947 Broken up 16 Mar 1956 K397 Blyth Dry Dock 27 May 1943 27 Nov 1943 20 June 1944 1947 Broken up 3 Aug 1959 K473 Smiths Dock, at Middlesbrough 23 Jun 1943 28 Dec 1943 18 May 1944 22 Nov 1945 to Canada as HMCS St. Thomas, 1944; sold for mercantile service 1946 (later SS Camosun III) K393 Smiths Dock, at Middlesbrough 25 Aug 1943 26 Jan 1944 3 Jul 1944 17 Feb 1946 to Canada as HMCS Kincardine; sold for mercantile service 1946 K405 Smiths Dock, at Middlesbrough 23 Sep 1943 10 Mar 1944 5 Sep 1944 16 Nov 1945 to Canada as HMCS Leaside; sold for mercantile service 1946 (later SS Coquitlam II) York Castle Ferguson Brothers, Port Glasgow 1944 20 Sep 1944 completed Feb 1945 as convoy rescue ship Blyth Dry Dock 29 June 1943 24 Feb 1944 15 Aug 1944 to Canada as HMCS Copper Cliff, 1944; Sold for mercantile service 1947, then became Chinese (People's Liberation Army) 1949 K384 William Pickersgill & Sons 23 Jan 1943 22 Apr 1943 12 Oct 1943 15 Feb 1944 Nov 1956 broken up 5 Jun 1958 K693 William Pickersgill & Sons 23 Jan 1943 23 Jun 1943 26 Nov 1943 13 Jul 1944 1946 broken up 9 Aug 1960 K446 William Pickersgill & Sons 23 Jan 1943 12 Aug 1943 26 Jan 1944 8 Oct 1944 to Canada as HMCS Bowmanville, 1944; Sold for mercantile service 1946, then became Chinese (People's Liberation Army) Kuang Chou 1949 K692 Harland and Wolff 23 Jan 1943 21 Jun 1943 11 Dec 1943 10 Mar 1944 1946 broken up 6 Sep 1960 K449 Harland and Wolff 23 Jan 1943 21 Jun 1943 11 Jan 1944 10 Jun 1944 Feb 1946 Became weather ship Weather Monitor in 1959 K398 Harland and Wolff 23 Jan 1943 21 Jun 1943 8 Feb 1944 26 Jun 1944 14 Mar 1946 to Canada as HMCS Arnprior, 1944; transferred to Uruguay as Montevideo K536 Fleming & Ferguson 23 Jan 1943 1944 8 Sep 1944 Jan 1945 Completed as convoy rescue ship (Empire Peacemaker) K453 Harland and Wolff 23 Jan 1943 21 June 1943 24 Feb 1944 14 Jul 1944 8 Mar 1946 to Canada as HMCS Petrolia, 1944; Sold for mercantile service 1946 K399 Ailsa Shipbuilding Company 23 Jan 1943 29 April 1943 13 Dec 1943 7 Apr 1944 Aug 1956 Broken up Jun 1958 K461 Ailsa Shipbuilding Company 23 Jan 1943 1 Jun 1943 24 Feb 1944 15 Jun 1944 15 Feb 1946 to Canada as HMCS Huntsville, 1944; Sold for mercantile service 1947 K386 S P Austin & Son Ltd 2 Feb 1943 31 May 1943 25 Nov 1943 24 Nov 1944 1947 Became the weather ship Weather Adviser in 1960 K387 Barclay Curle 2 Feb 1943 23 Apr 1943 19 Aug 1943 18 Nov 1944 1946 Scrapped 24 February 1956 K379 Caledon Shipbuilding & Engineering Company 2 Feb 1943 12 Mar 1943 31 Jul 1943 17 Nov 1943 1947 Scrapped 14 June 1958 K388 Caledon Shipbuilding & Engineering Company 2 Feb 1943 6 May 1943 28 Sep 1943 25 Feb 1944 1947 Scrapped March 1961 K416 Caledon Shipbuilding & Engineering Company 2 Feb 1943 6 August 1943 23 Feb 1944 9 Jun 1944 Sunk by U-482 on 1 Sep 1944 K362 Swan Hunter 6 Feb 1943 17 March 1943 21 Jun 1943 8 Nov 1943 1947 Scrapped 14 May 1958 K372 Swan Hunter 6 Feb 1943 8 April 1943 16 Jul 1943 24 Feb 1944 1946 Became the weather ship Weather Surveyor in 1960 K374 Swan Hunter 6 Feb 1943 5 May 1943 16 Aug 1943 24 Apr 1944 Transferred to Norway on completion and renamed HNoMS Tunsberg Castle; Sunk by mine 12 Dec 1944
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.
Royal Norwegian Navy – HMS Shrewsbury Castle was loaned to the Royal Norwegian navy on 17 April 1944. On 12 December 1944, she hit a mine and sank.
Cancelled 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.