1956 - 1988: Porpoise Class
This class was originally designated patrol submarines, then attack. They were the first conventional British submarines to be built after the end of World War II.
The Porpoise class were larger but shorter than their T Class predecessors and used a much improved steel known as UXW. This, and improved design and construction techniques allowed much deeper diving. It was found in tests that the unusually long engine room was liable to collapse, so there were extra large frames in this section, which proved to be something of an operational inconvenience.
Designed for 18 knots, they made 17 knots, which, with the use of silenced propellers, dropped to 16 knots. However, quieter running was felt to be a positive trade off for the reduced speed. The Porpoise class were exceptionally quiet underwater, more so than their NATO counterparts and far more so than the Soviet Whiskeys. This was in part due to careful attention to detail in the mounting of machinery, and advances made in propeller design to prevent cavitation. Initially, the silenced propellers actually set up a distinctive resonant 'singing', and it was said that HMS Rorqual was once identified leaving the River Clyde from a listening station from Long Island However, grooves were cut into the propellers and injected with a damping filler which cured the problem; HMS Rorqual was later able to surface undetected off the Statue of Liberty. The silent running abilities made their sonar equipment particularly effective.
They were far more capable than previous submarine classes in operating for prolonged periods thanks to much improved air recirculation and cleaning systems. The class also performed excellently in clandestine operations, such as surveillance and inserting special forces. The class were also the first since the R-class of 1917 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 Mark 24 Tigerfish torpedo. The Porpoise class boats 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.