Castle-class patrol vessel

The Castle-class was a class of British offshore patrol vessels of the Royal Navy. Two ships were constructed. Both were transferred to the Bangladesh Navy in 2010. The Bangladesh Navy upgraded them with more weapons and sensors. These ships are now reclassified as corvettes by the Bangladesh Navy.
Design.
The Castle-class was designed by David K. Brown and was intended as a series of six offshore patrol vessels for the Royal Navy, designed in response to criticism of the previous for insufficient speed, sub-optimal sea-keeping and lack of a flight deck for rescue helicopters.
In the event, only two ships were built, and . Both vessels were built by Hall Russell in Aberdeen, Scotland. These had significant improvements over the Island-class – they were 300 tonnes larger, more stable in heavy seas, faster and fitted with a large flight deck capable of supporting a Sea King helicopter. For brief periods, the ships could accommodate up to 120 troops.
Their primary mission was to serve with the Fishery Protection Squadron, protecting both the fishing fleets and the oil and gas fields of the North Sea. They could also serve as minelayers, and had detergent spraying facilities on board for dispersing oil slicks.
Operations.
After the Falklands War, one ship was kept long-term in the Falkland Islands as a guard ship. "Leeds Castle" and "Dumbarton Castle" rotated the role on a three-yearly basis, although the ship's crew usually did a six-month rotation.
Replacement.
The Castle-class was replaced in the Falklands by a unique vessel based on the , , and both vessels of the class were decommissioned. Originally due to transfer to the Pakistan Maritime Security Agency in 2007, the deal fell through and both ships were sold to the Bangladesh Navy.