HMS Rorqual
Porpoise-class
General Characteristics
Displacement:	2,080 tons surfaced/2,450 tons dived
Length:	290 ft (88.4 m)
Beam:	26.6 ft (8.11 m)
Draught:	18 ft (5.5 m)
Propulsion:	2 shafts, two 1650 hp (1.230 MW) Admiralty Standard range diesel generators, two English Electric main motors 12000 hp (8.95 MW)
Speed:	12 knots (22 km/h) surfaced/17 knots (31 km/h) dived
Range:	9,000 nautical miles at 12 knots (17,000 km at 22 km/h)
Complement:	71
Armament:	Eight 21 inch (530 mm) torpedo tubes (6 bow, 2 stern; 30 torpedoes in total)

The Porpoise class was an eight-boat class of diesel-electric submarines of the Royal Navy. This class was originally designated patrol submarines, then attack. They were the first submarines to be built after the end of World War II. Their design was, in many ways, influenced by the German WWII-era Type XXI U-boat, which was the first submarine that was designed to actually operate while submerged, unlike previous boats which could only operate underwater temporarily while being used more as a surface ship.

The Porpoise class were considerably quieter than their US counterparts, thanks in large part to a number of different techniques in the interior of the boat and the use of diesel-electric for the class. The class were relatively large compared to previous submarine classes, at 290 ft (88.4 m) and 2450 tons dived and had very effective long-range sensor equipment.

They were far more capable than previous submarine classes in operating for prolonged periods thanks to much improved underwater breathing systems. The class also performed excellently in clandestine operations, such as surveillance and inserting special forces. The class were also the first to not have a gun on deck, a decision that would be carried in all subsequent submarine classes in the RN.

The first Porpoise-class boats were launched in 1958 during the ever increasing threat of the Soviet Union's submarine fleet. The weaponry of the Porpoise-class was updated in 1970 to operate the Mk24 Tigerfish torpedo. The Porpoise-class were all decommissioned by the 1980s. The Oberon-class submarines, which were almost identical to the Porpoises, and the first of which was commissioned in 1961, survived their predecessor only a little longer, all being decommissioned in the early 1990s.