The River class was the last attempt by the Admiralty to produce "Fleet Submarines" that is submarines fast enough to operate as part of a fleet which at the time meant being able to manage somewhere around 20 knots (37 km/h) while surfaced. The previous attempts had been the steam powered K-class submarines and the large 12-inch (305 mm) gunned M-class submarines. 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, Severn and Clyde in 1935. The latter were a little larger than Thames. Initially 20 were planned but changes in thinking and cost limited the building to just the three.
The design compromised on diving depth to keep weight down and speed up. They had a safe diving depth of some 300 feet (90 m) compared to the Odin class before them which had managed 500 feet (150 m). They were powered by two diesel engines delivering 8,000 bhp (6,000 kW). Two Ricardo engines drove generators that supercharged the diesels up to 10,000 bhp (7,500 kW). This gave them a surface speed of 22 knots (41 km/h).
Thames was lost off Norway on 23 September 1940. Clyde was used to deliver supplies to the besieged island of Malta in September 1941. Severn and Clyde were in service in the Far East when they were taken out of service in mid to late 1945.