UK Navy tracks surface Russian Submarine in waters close to the UK.

According to information published by UK Navy on February 26, 2021, Royal Navy patrol ship HMS Mersey has tracked the movements of the surfaced Russian submarine B-237 Rostov-on-Don as it sailed through waters close to the UK.
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River-class offshore patrol vessel HMS Mersey and B-237 Rostov-on-Don Russian diesel-electric submarine Project 636.3 Varshavyanka (Picture source: UK Navy)

The River-class offshore patrol vessel was on watch as the Kilo-class diesel powered attack submarine RFS Rostov Na Donu sailed through wintry seas in the North Sea and English Channel on its journey from the Baltic to the Mediterranean.

Mersey reported on the movements of the Russian Black Sea Fleet submarine, so that NATO Allies could track her progress as she continued her onward journey.

Mersey was also on duty when the Kilo-class submarine made the reverse journey in October last year, as she returned from operations in the Mediterranean back to the Baltic.

The HMS Mersey is a River-class offshore patrol vessel (OPV) of the British Royal Navy. She was built by Vosper Thornycroft in Southampton to serve as a fishery protection vessel within the United Kingdom's waters along with her two sister ships Tyne and Severn. All three were commissioned into service in 2003 to replace the five older Island-class patrol vessels.

The River-class OPV is powered by two Ruston 12 RK 270 medium speed diesel engines, rated at 4,125 kW, 1,000 rpm, which drive twin controllable pitch propellers. She can sail at a maximum speed 200 knots (37 km/h) with a maximum cruising range of 5,500 nmi. (10,200 km). It has a crew f 20.