An Italian diver has discovered the wreck of a British World War II submarine that sank in 1942 with 71 servicemen on board.

Massimo Domenico Bordone, dubbed the "wreck hunter", spotted the ghostly wreck of the HMS P311 100 metres down off the north-east coast of Sardinia, near the island of Tavolara.

Mr Bordone said it looked like only the submarine's prow was damaged from the explosion, and it remained airtight as it sank.

"It looks like it probably went down with air sealed inside, leaving the crew to die eventually of oxygen deprivation," he said.

"Immediately I thought of the destiny of the men who met their deaths down there.

"It was a fate shared by so many men, submariners in particular, on both sides of the conflict."

HMS P311 set out from Malta on December 28, 1942 on a mission to torpedoing the Italian battleships Trieste and Gorizia as they lay at anchor in La Maddalena, a port off Sardinia's northern coast.

But the submarine disappeared without a trace after apparently hitting mines laid by the Italian navy to protect the island.

Local fisherman at the time reported hearing a loud rumble at night, but the 84-metre-long T-class vessel was never found.

The wreck boasted two Chariot manned torpedos, ready to be launched underwater to carry two navy divers into action.

The divers, known as frogmen, would enter enemy harbours on the Chariot and stick mines on enemy ships.

AFP