HMS H21

HMS H4, another submarine of the same class
History
United Kingdom
Name	H21
Builder	Vickers Limited, Barrow-in-Furness
Launched	20 October 1917
Commissioned	28 January 1918
Fate	Sold, 13 July 1926
General characteristics
Class and type	H class submarine
Displacement	423 long tons (430 t) surfaced 510 long tons (518 t) submerged
Length	171 ft 0 in (52.12 m)
Beam	15 ft 4 in (4.67 m)
Propulsion	1 × 480 hp (358 kW) diesel engine 2 × 620 hp (462 kW) electric motors
Speed	11.5 knots (21.3 km/h; 13.2 mph) surfaced 9 knots (17 km/h; 10 mph) submerged
Range	2,985 nmi (5,528 km) at 7.5 kn (13.9 km/h; 8.6 mph) surfaced 130 nmi (240 km) at 2 kn (3.7 km/h; 2.3 mph) submerged
Complement	22
Armament	4 × 21 in (533 mm) bow torpedo tubes 8 × 21 inch torpedoes

HMS H21 was a British H class submarine built by Vickers Limited, Barrow-in-Furness, as the first of the Batch 3 H class submarines. She was launched on 20 October 1917 and was commissioned on 28 January 1918. H21 was an improved design of the H class which produced a larger displacement and the latest 21 inch torpedo tubes replacing the old 18 inch torpedo tubes. This would be incorporated into all batch 3 H class submarines. HMS H21 was sold to John Cashmore Ltd on 13 July 1926 for scrapping at Newport.

Design

Like all post-H20 British H-class submarines, H21 had a displacement of 423 long tons (430 t) at the surface and 510 long tons (520 t) while submerged.^[1] It had a total length of 171 feet (52 m),^[2] a beam of 15 feet 4 inches (4.67 m), and a draught of 12 metres (39 ft).^[3] It contained a diesel engines providing a total power of 480 horsepower (360 kW) and two electric motors each providing 320 horsepower (240 kW) power.^[3] The use of its electric motors made the submarine travel at 11 knots (20 km/h; 13 mph). It would normally carry 16.4 long tons (16.7 t) of fuel and had a maximum capacity of 18 long tons (18 t).^[4]

The submarine had a maximum surface speed of 13 knots (24 km/h; 15 mph) and a submerged speed of 10.5 knots (19.4 km/h; 12.1 mph). Post-H20 British H-class submarines had ranges of 2,985 nautical miles (5,528 km; 3,435 mi) at speeds of 7.5 knots (13.9 km/h; 8.6 mph) when surfaced.^[1][3] H21 was fitted with an anti-aircraft gun and four 21 inches (530 mm) torpedo tubes. Its torpedo tubes were fitted to the bows and the submarine was loaded with eight 21 inches (530 mm) torpedoes.^[1] It is a Holland 602 type submarine but was designed to meet Royal Navy specifications. Its complement was twenty-two crew members.^[1]

References

1. Gardiner, Robert; Gray, Robert (1985). Conway's All the World's Fighting Ships 1906-1921. London: Conway Maritime Press. p. 92. ISBN 0-85177-245-5.
2. Derek Walters (2004). The History of the British 'U' Class Submarine. Casemate Publishers. pp. 2–. ISBN 978-1-84415-131-8.
3. Colledge, J. J.; Warlow, Ben (2006) [1969]. Ships of the Royal Navy: The Complete Record of all Fighting Ships of the Royal Navy (Rev. ed.). London: Chatham Publishing. ISBN 978-1-86176-281-8. Retrieved from Naval-History on 20 August 2015.
4. J. D. Perkins (1999). "Building History and Technical Details for Canadian CC-Boats and the Original H-CLASS". Electric Boat Company Holland Patent Submarines. Retrieved 20 August 2015.

Bibliography

• Hutchinson, Robert (2001). Jane's submarines : war beneath the waves from 1776 to the present day. London: HarperCollins. ISBN 9780007105588.