The Castle class was a class of British offshore patrol vessels of the Royal Navy. Two ships were constructed and after nearly 30 years service were sold to the Bangladesh Navy in 2010. The Bangladesh Navy upgraded these with more armaments including C-704 anti-ship missiles and sensors. These ships are now reclassified as corvettes by the Bangladesh Navy.

The River class is a class of offshore patrol vessels built primarily for the Royal Navy of the United Kingdom. A total of nine were built for the Royal Navy (RN), four Batch 1 and five Batch 2. One Batch 1 (HMS Clyde), which was the Falklands guard ship, was decommissioned and transferred at the end of its lease to the Royal Bahrain Naval Force.