Requirements for the new class (defined as Patrol Submarines) demanded that they have a strong armament and a patrol duration of at least 42 days. Restricted by the limitations imposed by the London Naval Treaty, which allowed only 16500 tons total of new construction submarines, the class was designed to have a displacement of about 1575 tons so that a sufficient number could be built. The first-of-class, approved in the 1935 Programme, was built at Vickers and entered service in December 1938 under the name of Triton.
Fifty-three T Class submarines were eventually constructed, making it the largest class of ocean-going submarines ever built for the Royal Navy: the original order for the class was made under the growing threat of war, which forced the Admiralty to open its purse strings, and no fewer than 21 riveted-hull T boats, built between 1937 and 1941, followed Triton.
Displacing almost 400 tons less than the Oberon Class, Parthian Class and Rainbow Class, this first group of 22 T Class submarines were noted for their simplicity of construction. They were superior to the Oberon Class, Parthian Class and Rainbow Class in that they had greater submerged speed, better surface and underwater handling and more torpedo tubes. However, because the displacement limitations restricted the size and power of their engines to 2500 hp (surfaced) (1450 hp submerged), the maximum surface speed was lower.
The first T Class submarines were 275 feet long and displaced 1327 tons surfaced. Their 'surface' armament included one 4-inch gun and three 0.303-inch machine-guns, which were later replaced by, or supplemented by, one 20mm Oerlikon cannon. They were the last Royal Navy submarines designed for overseas patrol to have insufficient range for the Pacific.
THE WAR YEARS
Under the 1940 War Programme came the decision to build nine slightly modified T Class submarines. These modifications were made in the light of experience gained with the first group of T boats and the main changes were in the number and disposition of torpedo tubes, the outer hull shape and the use, in most of the modified vessels, of an electrically welded, rather than a riveted, construction. The latter change assisted deeper diving, improved the resistance to depth charge attack, and also enabled the shipbuilder to adopt the new technique of prefabricating the hull in sections in the shops and assembling large units at the building berth.
To this modified group of submarines was fitted, at the extreme stern, an additional external torpedo tube, whilst the two tubes amidships were repositioned aft of the conning tower, angled to fire astern. These changes altered the shape and silhouette of the class, as did the removal of the bulbous bow casing which had created a notable bow wave which, when running at periscope depth, hampered visibility and the correct trim of the boat. As a result of these alterations, the second group of boats were more streamlined, and the openings for the two external tubes were more clearly visible.
The two faces of T Class submarines. Above: one of the first - HMS Tally-Ho and, below, HMS Taciturn showing the radical changes that resulted from the 1951/56 rebuilding programme.
In addition to their eleven 21-inch torpedo tubes. Group 2 T Class submarines were fitted with a 4-inch gun, a 20mm Oerlikon cannon on a platform aft of the periscopes and three 0.303-inch machine-guns on removable mountings.
Additional orders in the 1941 and 1942 programmes meant that a total of 31 modified T Class submarines entered service between 1942 and 1946. 21 of which were laid down at Vickers, although a number of these were completed at other yards. Of the 22 Group 1 submarines constructed, eight were built exclusively at Barrow, along with other British submarines. The T boats ordered in the 1941 and 1942 programmes were fitted with surface and air search radar sets.
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 to the highest loss rate. For example, 13 boats were lost in the Mediterranean, despite the fact that large enemy vessels were very vulnerable in that sea. Nevertheless, the T Class were particularly successful against submarines, and 13 boats (six of which were Barrow-built) sank 13 enemy submarines: six Italian, four German and three Japanese.
In January 1943, Thunderbolt, ex Thetis, transported 'chariot' type assault craft which penetrated the harbour of Palermo and sank the hull of the Italian light cruiser Ulpio Traiano, which was being fitted out. Other major successes included the sinking of two cruisers - the 5700-ton Kuma and the 13 000-ton Ashigara - by the 'Barrovians' Tally-ho and Trenchant respectively, whilst, in August 1941, another Vickers boat, the Triumph, managed to seriously damage the 12 000-ton cruiser Bolzano.
At the end of the war, Group 1, Group 2 and some Group 3 submarines were placed in reserve, scrapped or ceded to other countries. Those remaining in service largley unmodified, are shown in Diesel Submarines 1948 - 1958
In addition other T class submarines were modified significantly. Five T class - Tireless, Token and the Barrow-built Tapir, Talent and Teredo were streamlined and fitted with improved battery cells, modern sonar and a fin-shaped conning tower is described in A fresh look at the Five Streamlined T class submarines of the early 1950s
In 1951-56, eight of the welded-hull boats were completely rebuilt in a manner similar to the
American 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 a new section added to their length, they were streamlined and their underwater propulsion capacity was increased by a factor of four to give 15 knots, nearly twice the previous submerged speed, and with increased endurance at at slow submerged speeds
For more detail see T Class Conversion and Diesel Submarines 1948 - 1958
Though wartime experience had shown the maximum surface speed of 15 knots was not sufficient, in the post war conversions this was apparently not considered a major disadvantage in the circumstances of the Cold War. This presumably due the change to major transits by snort as discussed in Snorting in the Royal Navy, 1945 onwards. Although in later years their speed was judged to be inadequate, a proof of their high reputation for reliability is demonstrated by T Class submarines, which after many refits, were still in active service with a Foreign Navy in the early 1970's.
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