River-class submarine

British River-class submarine (HMS Severn)
Class overview
Name:	River class
Operators:	Royal Navy
Preceded by:	S class
Succeeded by:	Grampus class
Completed:	3
Lost:	1
Retired:	2
General characteristics
Type:	Submarine
Displacement:	2,206 tons surfaced (Thames 2,165 tons) 2,723 tons submerged (Thames 2,680 tons)
Length:	345 ft (105 m)
Beam:	28 ft 3 in (8.61 m)
Draught:	15 ft 11 in (4.85 m)
Propulsion:	2 shaft diesel electric 2 supercharged diesels 10,000 hp (7,500 kW) max 2 electric motors 2,500 hp (1,900 kW)
Speed:	22 knots (41 km/h) surfaced 10 knots (19 km/h) submerged
Complement:	61
Armament:	6 × 21-inch (533 mm) torpedo tubes (bow) 1 × QF 4-inch (101.6 mm) Mk XII deck gun

The River class, or Thames class were a class of submarines built for the Royal Navy. Operating during the Second World War, the three boats of the class comprised Thames, Severn and Clyde. All the submarines were named after rivers in the United Kingdom. One was lost during the war and the rest taken out of service following it.

The River class was the last attempt by the Admiralty to produce "fleet submarines", 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).