In October 1917, 12 R boats were ordered from five yards and R7 was the first to be completed, at Vickers, in June 1918 within nine months of order. Vickers also constructed R8. A further. two boats that were to be built at Pembroke Dockyard, R5 and R6, were cancelled before launch.
The R boats' surface speed of 9.5 knots was attained from one 240 bhp engine of the H Class type and their two main motors, driven by 220 battery cells, generating 1200bhp. Also, the fact that the class could reach a submerged speed of 15 knots, which remained a record until the closing stages of the Second World War, was partly due to their lightened superstructure, which was cut to a bare minimum, and a streamlined fish-shaped hull.
From war experience, designers became rather optimistic in their assessment of diving depths and the designed diving depth of the R Class was given as 250 feet, but the operational diving depth would have been fixed at 150 feet.
The R Class were the first Royal Navy submarines to be fitted with six 18-inch bow torpedo tubes, which was a powerful torpedo armament for the size of boat. One spare torpedo was allowed for in the design, but during the war, six spares were stowed at the expense of the Senior Ratings' accommodation. Originally it was intended to fit a 4-inch gun forward of the bridge, but this was never adopted, as it would have had an adverse effect on submerged speed, which was the main characteristic of the design.
Having a greater submerged radius than most submarines of the period, the R boats used five hydrophones to detect submerged enemy vessels: had they been fitted with a better detection device, the development of the modern submarine may have gone ahead more quickly. An R boat is credited with torpedoing a U-Boat in October 1918 - had the torpedo exploded, the R boats might have earned more respect instead of being thought of as curiosities.
