Submarine of the Royal Navy
 HMS H4, another submarine of the same class
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| 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 | |
| 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 | |
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]
