HMS Unrivalled was one of the second group of U-class submarines ordered on 23 August 1940.[1] These submarines differed from their predecessors in that they were lengthened by 5feet "to give a more streamlined shape aft and to improve the flow of water over the propellers."[2]
The submarine was 195inchesft6inchesin (ftin) long and 15inchesft9inchesin (ftin) abeam. Unrivalled had a single hull with internal ballast tanks and had a draft of 15inchesft19inchesin (ftin) when surfaced. She displaced 735LT while submerged, but only 648LT on the surface.[3] The submarine was equipped with two diesel engines and twin General Electric electric motors—for surfaced and submerged running, respectively. They were coupled together with a diesel-electric transmission. Unrivalled had a surface speed of up to 11.25kn and could go as fast as while underwater. The boat could carry up to 55LT of diesel fuel, giving her a range of 5000nmi at . Her electric motors and batteries provided a range of at while submerged.[1]
HMS Unrivalled was equipped with four 21inches bow torpedo tubes and could carry eight torpedoes. The submarine was also armed with a 3inches QF Mk I gun deck gun. She had a crew of 33 men.[1]
HMS Unrivalled was ordered on 23 August 1940 as part of the 1940 naval construction programme from Vickers-Armstrong at Barrow-in-Furness.[1] She was laid down on 12 May 1941, launched on 16 February 1942 and commissioned on 3 May 1942.[4]
Apart from a work-up patrol in the Norwegian Sea, she spent the bulk of the war in the Mediterranean. While working up, Unrivalled fired a torpedo at what was thought to be a submerged enemy submarine. Only the periscope was sighted, and the torpedo was fired in the direction detected by the hydrophones, but no German submarine was in the area. Whilst in service in the Mediterranean, she sank a number of small merchantmen and small naval auxiliary vessels with both torpedoes and gunfire. These included the Italian auxiliary submarine chaser O 97 / Margherita, the Italian merchants Maddalena, Mostaganem and Pasubio, the Italian tugs Genova and Iseo, the Italian sailing vessels Triglav, Albina, Margherita, Sparviero and Ardito, the German auxiliary submarine chasers UJ 2201/Bois Rose and UJ 2204/Boréal, the Italian tanker Bivona, the small Italian merchant Santa Mariana Salina, the Italian auxiliary minesweeper R 172 / Impero and the small Italian vessel San Francisco di Paola A.[4]
Unrivalled also damaged the on 3 December 1942, but neither sank or damaged any Axis ships after 28 July 1943.[4] During Operation Husky in July 1943, she was stationed offshore to mark the landing beaches for the 1st Canadian Infantry Division.[5] The boat survived the war, but was too slow for requirements and was not retained after the war.[1] She was scrapped at Briton Ferry, Wales, beginning on 22 January 1946.[4]