British U-class submarine

U-class submarine HMS Ultimatum departing Holy Loch, August 1943
Class overview
Name	U class
Operators	Royal Navy  Polish Navy  Free French Naval Forces  Soviet Navy  Royal Netherlands Navy  Royal Danish Navy  Hellenic Navy  Royal Norwegian Navy
Preceded by	T class
Succeeded by	V class
Completed	49
General characteristics
Type	Submarine
Displacement	540 long tons (550 t) standard, 630 long tons (640 t) full load surfaced 730 tons submerged
Length	191 ft (58 m)
Beam	16 ft 1 in (4.90 m)
Draught	15 ft 2 in (4.62 m)
Propulsion	2 shaft diesel-electric 2 Paxman Ricardo diesel generators + electric motors 615 hp (459 kW), 825 hp (615 kW)
Speed	11.25 kn (20.84 km/h; 12.95 mph) surfaced 10 kn (12 mph; 19 km/h) submerged
Range	4,500 nmi (8,300 km; 5,200 mi) at 11 kn (20 km/h; 13 mph) surfaced
Complement	27 to 31
Armament	6 × 21 inch (533 mm) torpedo tubes - 4 bow internal, 2 bow external (first group only) 8–10 torpedoes 1 × QF 3 inch 20 cwt 3 in (76 mm) gun

The British U-class submarines (officially "War Emergency 1940 and 1941 programmes, short hull")^[1] were a class of 49 small submarines built just before and during the Second World War. The class is sometimes known as the Undine class, after the first submarine built. A further development was the British V-class submarine of 1942.

At the start of the Second World War the U class was, with the British S Class and T class submarines, the Dutch O 21 class and German Type VII class one of the most advanced submarine classes in service.^[2]