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
