Porpoise Class submarines were fitted with two Admiralty Standard Range 16-cylinder diesel generator sets. Together these supplied 3300 bhp, providing a surface speed of 12 knots. The submerged speed of 17 knots was attained from two massive main batteries which drove the propulsion motors, developing 5000 hp.
Having beautifully clean welded hulls and a high yet silent underwater speed, these submarines were among the best conventional boats in the world for their day. Long patrol endurance was a primary design requirement of the Porpoise Class, and the snort equipment was designed to give maximum snort charging facilities and to operate in rough sea conditions in any part of the world. When required, oxygen replenishment and carbon dioxide and hydrogen eliminators made it possible for the class to remain totally submerged for several days without 'snorting'.
When snorting, these submarines remained submerged for as long as six weeks. They were fitted with apparatus to distil freshwater from sea-water for drinking purposes, and this, together with stowage capacity for large quantities of stores and provisions, enabled them to remain independently operational for months without any outside support. With this ability to stay at sea for such long periods, habitability standards had to be of the highest quality, and an air conditioning plant, which provided drying and either heating or cooling of the air as appropriate for arctic or tropical service, was an important installation in the Porpoise Class.
Of the last exponents of the class, the Barrow built Porpoise was sunk as a target on 20th October 1985, whilst Rorqual was broken up in the same year, Sealion and Walrus were sold in 1987 and Finwhale was broken up in the same year.
