In 1951-56, eight of the welded-hull boats were completely rebuilt in a manner similar to the American Greater Underwater Propulsive Power 'Guppy' Programme. The eight converted were: Tabard; Truncheon; Thermopylae; Totem; Turpin and the Vickers-built Trump, Tiptoe and Taciturn. Their hulls were cut. in two and new sections added to their length. They were streamlined and their underwater propulsion capacity was increased enormously to give twice the previous submerged speed and increased endurance. At the same time, sensing and detection equipment was updated.
Although in later years their speed of 15.25 knots surfaced and 9 knots submerged was judged to be inadequate, proof of their high reputation for reliability is demonstrated by those T Class submarines which, after many refits, were still in active service with a Foreign Navy in the early 1970s.
