Group Three 1940 Programme
Large Patrol Submarine
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This class were built as a replacement for the 'P' class and were very often referred to as the 'Replacement 'P'. They were some 400 tons smaller than the 'O', 'P' and 'R' classes but were superior in just about every other aspect except surface speed as their displacement meant they could be fitted with less powerful diesel engines.
It was intended to fit the first group with different types of engines so an evaluation could be done on the differing types, the commencement of WWII halted this and the remaining boats were either fitted with Vickers or Admiralty design diesel units.
The first batch were of an all riveted design and their torpedo tubes were arranged to fire forward, this was modified in all later boats which had an external stern tube fitted. The two external midships tubes were moved further aft and also turned to fire astern. Another disadvantage of this first batch were the forward external tubes. These were encased in a bulbous casing which caused a bow-wave which proved to be an obstruction when using the periscope. These modifications were carried through to the Second group.
The Third group benefited from all the above and also was fitted with a 20mm Anti-aircraft gun aft of the conning tower as well as being fitted with RDF. These modifications were eventually carried out on all the class with the exception of losses.
Some of this Third group were partially of a welded structure and eventually of a complete welded structure. The boats which were completely welded were transferred to the Far East as some of their tanks were converted to carry fuel which gave them a much larger radius of operation.
The longest patrol carried out by a British submarine was recorded by Tantalus who spent 56 days.
The class proved to be most successful and were employed in all theatres of WWII, they suffered their greatest losses in the Mediterranean which was not suited to large submarines. After the end of WWII some of the 'T' class were streamlined: Five of the riveted hull boats of which were Tapir, Tireless, Talent, Teredo and Token were modernised with up to date sonar and fitted with a fin type conning tower.
In the 1950's eight of the welded type were completely rebuilt, their hulls were cut in two and lengthened. Improvements were made to the propulsion units both electric and diesel, modern noise reduction techniques were fitted as well as new sensors, these also were fitted with a fin type conning tower.
The eight were: Tabard, Trump, Truncheon, Tiptoe, Taciturn, Thermopylae, Totem and Turpin.
1 x 20mm HA Oerlikon.
3 x 0.303 Lewis or Vickers Mg.
11 x 21 inch tubes, 8 fwd, 2 amidships and 1 aft.
17 reloads or 12 MkII mines.