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 east coast of Britain. They were designed to be built in large numbers in small shipyards and 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. The Flowers were unsuited for open-ocean escort missions 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. The Royal Navy recognized the limitations of the Flower and began designing an open-ocean escort in November 1940, which became the . The larger Rivers were too expensive to produce at the required rate and needed larger slipways. In response, the was developed in late-1942, which was developed from the River and designed for prefabricated construction. The Castle was developed from a proposal by Smith's Dock Company – who had designed the Flower-class – for a stretched Flower. The result was a scaled-down version of the Loch for shipyards that only build 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. Design The Castle resembled later Flowers with an extended forecastle and mast behind the bridge, but was 420 tons heavier and 37 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. A lattice mainmast was used instead of the pole version fitted to the Flowers. Construction