The M class were K-class hulls re-engined with diesels and modified to take a single 12 in (305 mm) naval gun directly forward of the conning tower.

A design was drawn up in the late 1920s and three vessels were built by Vickers in Barrow: Thames in 1932, and Severn and Clyde in 1935.

During the Second World War, they initially operated in the North Sea and Mediterranean, then moved to the Far East in the latter stages.

Clyde and Severn set sail from Gibraltar heading to take up station in Freetown on 31 August 1939, just four days before the outbreak of hostilities.

On their arrival, they joined South Atlantic Command and were tasked with convoy defence duties.

When it is discovered, it is highly likely that it is to be left alone, because like all ships lost in wartime, it is considered to be a war grave.

It would be used in the aftermath of the Battle of the River Plate to hunt for German Surface Raiders and their support ships.