Instantly recognizable as a result of their oddly cranked profiles, the T class boats were the Royal Navy's standard wartime patrol submarines. Between HMS Triton and Tabard, launched in October 1937 and November 1945 respectively, the class reached a respectable 54 in number. With the 'Thames' class abandoned for the reasons discussed and a replacement required for the unsatisfactory 'O1 class, the T class design needed not only to rectify shortcomings but also to conform to the treaty agreements that bedevilled mterwar planning. The London Naval Treaty limited total (rather than individual) displacement so, to obtain maximum numbers of boats, a 1,000-ton target was set. Into this a 42-day endurance was to be packed. That the final result was only some 9 per cent heavy, while being highly reliable, was a credit to the design team.
Because of their limiting parameters, the T class boats could ship only small-sized diesels and their surface speed was thus modest, In contrast they carried a large punch, the six forward tubes within the pressure hull being augmented by a pair in the bulged bow casing and a further pair in the casing, one on each side of the tower. Thus, a 10-torpedo forward salvo could be fired, albeit at the cost of a highly individual profile.
This arrangement applied to all 22 boats built before World War II, later units having the amidships tubes taken farther aft and reversed, and a single tube added in the casing right aft, Warbuilt boats also had their bows altered to set the external tubes higher, and some external ballast tanks converted to bunker space. Oil fuel capacity was almost doubled and the endurance of the boat became more than that of her crew and their supplies.
Fourteen of the pre-war boats were lost, mainly in the Mediterranean. Those from the wartime programmes were completed largely after the end of the Mediterranean war and only one was lost at sea. Post-war many were sold, while others were stretched and streamlined, serving alongside their successors, the A' class, until the late 1960s. Four units were cancelled and another only projected.
Specification 'T' class Displacement: 1,325 tons surfaced and 1,570 tons submerged Dimensions: length 83.82 m (275.0 ft); beamS. 10 m (26.58 ft); draught 4,50 m (14.75ft) Propulsion: two diesels delivering 1864.25 kW (2,500 bhp) and two electric motors delivering 1081.3 kW ( 1,450 hp) to two shafts Speed: 15.25 kts surfaced and 9 kts submerged Endurance: 20382 km (12,665 miles) at 10 kts surfaced Armament: one 101.6-mm(4-in)gun and 10 or 11533-mm (21-in) torpedo tubes (in first group 10 bow and in second group eight bow and three 3tern) Complement: 56 (first group) or 61 (second group)