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 was 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, most T Class submarines were placed in reserve, taken out of service or ceded to other countries. Most of the early T Class with riveted hulls could not be fully modernized, but five - Tireless, Token and the Barrow-built Tapir, Talent and Teredo - were streamlined and completely refitted with six bow tubes, modern sonar and a fin-shaped conning tower.
