During the Second World War, T Class submarines operated. successfully in all the theatres in which the Royal Navy was committed and many of the Group 2 boats were further modified for employment in the Far East. Several ballast tanks were changed into fuel tanks, thereby increasing the fuel load from 132 to 230 tons and surface range from 8000 to 11 000 miles at 10 knots. In a theatre where it took up to a week to sail from base to the operational area, this increase in range, together with increased stores capacity, enabled long patrols to be carried out - the record being 56 days by the Barrow-built Tantalus, 40 days of which were spent in the patrol area.
Although the T Class obtained satisfactory results, the fact that they were one of the classes which bore the brunt of Second World War submarine operations meant that they were subjected
