P 311 was the only unnamed T-class boat, she was due to have been named Tutenkhamen but lost before she could be renamed. She was fitted to carry 2 Chariot human torpedoes.

HMS P 311 (Cdr. Richard Douglas Cayley, DSO and 2 Bars, RN) was lost while engaged in Operation Principle, the Chariot attack on Italian cruisers at La Maddalena. HMS P 311 left Scotland in November 1942 with sister-boats HMS Thunderbold and HMS Trooper after addition of human torpedo deck-mounted watertight containers, direct for Malta. P 311 departed from Malta on 28 December 1942. She sent her last signal on 31 December 1942 from position 38º10'N, 11º30'E. After this signal she was not heard from again and she is presumed sunk by Italian mines in the approaches to Maddalena on or around 2 January 1943. She was reported overdue on 8 January 1943 when she failed to return to base.

Commanding Officer:
Cdr. Richard Douglas Cayley, DSO and 2 Bars, RN
8 June 1942 - 8 January 1943