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 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: 7 Built
Traveller and Trooper were fitted with Admiralty Diesels.
Trusty and Turbulent were fitted with Vickers Diesels.
3 x o.303 Lewis or Vickers MG.
11 x 21 inch tubes, 8 fwd, 2 amidships and 1 aft.
17 reloads or 12 MkII mines.
1943 Thrasher and Trusty 1 x 20mm HA Oerlikon added.