R-class submarine
History
United Kingdom
Name	HMS R4
Builder	Chatham Dockyard, Kent
Laid down	4 March 1917
Launched	8 June 1918
Commissioned	23 August 1919
Nickname(s)	"The Slug"
Fate	Sold, 26 May 1934
General characteristics
Class and type	R-class submarine
Displacement	410 long tons (417 t) surfaced 503 long tons (511 t) submerged
Length	163 ft 9 in (49.91 m)
Beam	15 ft 3 in (4.65 m)
Draught	11 ft 6 in (3.51 m)
Installed power	240 bhp (180 kW) (diesel) 1,200 hp (890 kW) (electric)
Propulsion	1 × diesel engine 1 × electric motor
Speed	9.5 knots (17.6 km/h; 10.9 mph) surfaced 15 knots (28 km/h; 17 mph) submerged
Range	2,400 nmi (4,400 km; 2,800 mi) at 9 knots (17 km/h; 10 mph) surfaced; 60 nmi (110 km; 69 mi) at 5 knots (9.3 km/h; 5.8 mph) submerged
Test depth	150 feet (45.7 m)
Complement	2 officers and 20 ratings
Sensors and processing systems	Bow hydrophone array
Armament	6 × bow 18-inch (45 cm) torpedo tubes

HMS R4 was one of 10 R-class submarine built for the Royal Navy during the First World War. The boat was not completed before the end of the war and was sold for scrap in 1934.

The R-class submarine was designed to meet an Admiralty requirement for a specialised hunter-killer submarine with an emphasis on submerged performance. The boats had a length of 163 feet 9 inches (49.9 m) overall, a beam of 15 feet 3 inches (4.6 m) and a mean draft of 11 feet 6 inches (3.5 m). They displaced 410 long tons (420 t) on the surface and 503 long tons (511 t) submerged. The R-class submarines had a crew of 2 officers and 20 ratings.^[1] They had a diving depth of 150 feet (45.7 m).^[2]

For surface running, the boats were powered by a single eight-cylinder ^[3] 240-brake-horsepower (179 kW) diesel engine that drove the single propeller shaft. When submerged it was driven by a 1,200-horsepower (895 kW) electric motor. They could reach 9.5 knots (17.6 km/h; 10.9 mph) on the surface and 15 knots (28 km/h; 17 mph) underwater. On the surface, the R class had a range of 2,400 nautical miles (4,400 km; 2,800 mi) at 9 knots (17 km/h; 10 mph) and 60 nmi (110 km; 69 mi) at 5 knots (9.3 km/h; 5.8 mph) submerged.^[4]

The boats were armed with six 18-inch (45 cm) torpedo tubes in the bow. They carried six reload torpedoes for a grand total of a dozen torpedoes. They were equipped with an array of five hydrophones in the bow to allow them to locate and engage targets while submerged.^[4]

HMS R4 was laid down on 4 March 1917 at Chatham Dockyard, launched on 8 June 1918 and commissioned on 23 August 1919. She came too late to see any combat in World War I, like most of the other R-class submarines. Her shape resulted in her being nicknamed "The Slug".^[5]

On 1 November 1926, R4 ran aground at Exmouth, Devon, England. She was refloated 10½ hours later.^[6]

R4 was the only boat to survive through to the 1930s. Additions to her casing produced slightly better sea keeping at the cost of a reduced speed from 15 knots submerged to 13 knots. She was used as a fast underwater target at the Portland anti-submarine school until 1934, then sold on 26 May 1934 to Young, Sunderland.

• Akermann, Paul (2002). Encyclopaedia of British Submarines 1901–1955 (reprint of the 1989 ed.). Penzance, Cornwall: Periscope Publishing. ISBN 1-904381-05-7.
• 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.
• Gardiner, Robert & Gray, Randal, eds. (1985). Conway's All the World's Fighting Ships 1906–1921. Annapolis, Maryland: Naval Institute Press. ISBN 0-85177-245-5.
• Harrison, A. N. (January 1979). "The Development of HM Submarines From Holland No. 1 (1901) to Porpoise (1930) (BR3043)". RN Subs. Retrieved 27 September 2022.