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