Runnymede-class

The River class, designated Fleet Minesweepers (MSF), was developed for the British Royal Navy during the 1980s to replace the Ton class. The design was based on commercial offshore support vessels, a concept refined through the use of chartered trawlers. Richards (Shipbuilders) Ltd constructed twelve vessels at yards in Lowestoft and Great Yarmouth.

The class featured a traditional steel hull designed for deep-sea operations and ocean environments, with the capability to remain at sea for extended periods without support. Developed to counter deep-water buoyant moored mines, the vessels utilized the Wire Sweep Mark 9 system to perform Extra Deep Armed Team Sweeping (EDATS). This process involved ships operating in pairs or formations to tow a sweep that followed the seabed profile to cut mine moorings. The system also supported influence sweeping by using a towed transducer to generate acoustic and electro-magnetic signatures. Armament consisted of a manually operated Bofors gun and general-purpose machine guns.

Upon entering service, the class joined the 10th Mine Countermeasures Squadron at Rosyth. Most vessels were assigned to various Royal Naval Reserve divisions, though HMS Blackwater operated with the regular Royal Navy. Following a 1993 review of reserve forces, the class was withdrawn from reserve service. A subset of the class, including Blackwater, Spey, Arun, and Itchen, was reassigned to the Northern Ireland Squadron to conduct counter-terrorist operations and waterway patrols. HMS Orwell served as a training ship beginning in 1994. Between 1994 and 2001, the Royal Navy decommissioned the class and sold the units to the navies of Bangladesh, Brazil, and Guyana. In these roles, the vessels have been utilized as patrol corvettes, survey ships, buoy tenders, and coast guard vessels.