HMS R3 was one of 10 R-class submarine built for the Royal Navy during the First World War.

On the surface, the R class had a range of 2,400 nautical miles (4,400 km; 2,800 mi) at 9 knots (17 km/h; 10 mph) and 60 nmi (110 km; 69 mi) at 5 knots (9.3 km/h; 5.8 mph) submerged.

They were equipped with an array of five hydrophones in the bow to allow them to locate and engage targets while submerged.

[4] HMS R3 was laid down on 4 February 1917 at Chatham Dockyard, launched on 8 June 1918 and commissioned on 17 March 1919.

She came too late to see any combat in World War I, like most of the other R class submarines.