HMS R4

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)". Submariners Association: Barrow in Furness Branch. Archived from the original on 19 May 2015. Retrieved 19 August 2015.