British R-class submarine

The R-class submarines were a class of 12 small British diesel-electric submarines built for the Royal Navy during World War I, and were forerunners of the modern hunter-killer submarines, in that they were designed specifically to attack and sink enemy submarines, their battery capacity and hull shape being optimized for underwater performance.

With a submerged speed of 14 kn, the class set an underwater speed record not broken until the experimental Japanese Submarine No.71 of 1938, which was capable of more than 21 kn submerged.

Description
Ordered in December 1917, the R-class were designed to be faster underwater than on the surface, achieving a submerged speed of 14 kn versus a surfaced speed of 9 kn. They were well-streamlined, having no external ballast tanks, casing, or deck gun, and a streamlined spindle-shaped hull of circular cross-section (not reproduced until the Los Angeles-class) which tapered sharply towards the stern and allowed only for a single screw. The bulbous bow contained five sensitive hydrophones and the lightened conning tower was also well-streamlined.

Thirty-five percent of the space inside the pressure hull was occupied by machinery. A single 8-cylinder 480 hp Diesel engine was installed for surface propulsion, while high underwater speed was given by two large electric motors arranged one behind the other to drive the single propeller shaft, and powered by a 200-cell battery of the same type fitted to J-class submarines. The large battery was, however, sufficient for only about an hour at full power. In addition, the engine took a full day to charge the batteries, using half its power. Charging was therefore undertaken in harbour, using a supply of electricity from the shore or from special battery charging vessels.

Despite being designed for maximum underwater performance, the R-class submarines were extremely difficult to control submerged, especially at high speeds. Surfaced, they had poor seakeeping and were slow. Minor modifications were made to R4, the only submarine of the class to survive into the 1930s, which made it more manageable on the surface, but reduced its submerged speed to a maximum 13 kn.

Armament
The R-class were the first Royal Navy submarines to be fitted with six bow torpedo tubes, number of torpedoes being considered more important than range or size of warhead carried when attacking U-boats. The torpedo tubes were originally the smaller 18 in but later changed to 21 in. As designed, one spare torpedo was allowed for, but in operation six reloads were carried in place of the senior Ratings' accommodation. It was originally intended to fit a 4 inch gun on the foredeck, but this was dropped due to the adverse effect it would have had on submerged speed.

Construction
R-1 through R-4 were ordered from Chatham, R-5 and R-6 from Devonport (later changed to Pembroke), R-7 and R-8 from Vickers, R-9 and R-10 from Armstrong, and R-11 and R-12 from Cammell Laird. In August 1919, with World War I over, R-5 and R-6 were cancelled, the rest being completed. To save time, they used H-class components.

Service
Operating out of Killybegs, Donegal, one of the class reportedly tracked and fired on a U-Boat in October 1918, firing a full salvo of six torpedoes of which only one hit but did not detonate.

All but R-4 and R-10 were sold for scrap in 1923. The two survivors were relegated to ASW training at Portland, where their high performance led to them (literally) running rings around naval trawlers whose performance their crews found deficient. R-10 was sold in 1929, while R-4 survived as a fast underwater target at Portland until 1934.

R-class submarines
* Cancelled while under construction
 * HMS R1
 * HMS R2
 * HMS R3
 * HMS R4
 * HMS R5 *
 * HMS R6 *
 * HMS R7
 * HMS R8
 * HMS R9
 * HMS R10
 * HMS R11
 * HMS R12