 Ordered in December 1917, the R class were designed to be faster underwater than on the surface, achieving a submerged speed of versus a surfaced speed of .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 American USS "Albacore") 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.