HMS H21

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.

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 & 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

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]