HMS Unrivalled (P45) was a U-class submarine built for the Royal Navy during World War II.

She sank a number of small merchant ships and naval auxiliaries, but major success eluded her during the war.

[1] These submarines differed from their predecessors in that they were lengthened by 5 feet (1.5 m) "to give a more streamlined shape aft and to improve the flow of water over the propellers.

The boat could carry up to 55 long tons (56 t) of diesel fuel, giving her a range of 5,000 nautical miles (9,300 km; 5,800 mi) at 10 knots (19 km/h; 12 mph).

Her electric motors and batteries provided a range of 120 nautical miles (220 km; 140 mi) at 2 knots (3.7 km/h; 2.3 mph) while submerged.

[4] During Operation Husky in July 1943, she was stationed offshore to mark the landing beaches for the 1st Canadian Infantry Division.