The Bangladesh Navy upgraded these with more armaments including C-704 anti-ship missiles and sensors.

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 Island class for insufficient speed, sub-optimal sea-keeping and lack of a flight deck for rescue helicopters.

These had significant improvements over the Island-class – they were 300 tonnes larger, more stable in heavy seas, 3 knots (5.6 km/h; 3.5 mph) faster and fitted with a large flight deck capable of supporting a Sea King helicopter.

They could also serve as minelayers, and had detergent spraying facilities on board for dispersing oil slicks.

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.