The wreckage of a British World War II submarine that sank 70 years ago in the Mediterranean Sea has been discovered seven miles away from Malta and in doing so a World War II British mystery has been solved.

On 8 May 1942, under cover of darkness, the British submarine HMS Olympus (N35) was attempting to leave the British Naval Base in the Grand Harbour of Malta, at a time when Malta was blockaded by the Germans and Italians.

But the Olympus didn’t get far before striking a mine and sinking.

Only 11 of the 98 men aboard survived, swimming about seven miles in cold water and without lights to guide them due to the wartime blackout.

Olympus was stationed out of Malta but many of her crew trained in Gosport and lived in the Portsmouth area.

Archivist George Malcolmson, of the Royal Naval Submarine Museum in Gosport, said: “In terms of men killed, the loss of HMS Olympus ranks as one of the worst Royal Navy wartime submarine losses.

“There were just 11 survivors. One of these was the famous Gordon Selby, a legend in the submarine service for surviving the sinking of several boats during the war.

“Gordon once told me that his lasting memory of the sinking of Olympus was looking back at the submarine as she settled in the water and there he saw a mass of boots and shoes neatly placed in one long line on the upper deck casing.

“The footwear was placed there by the survivors of the initial mine explosion before they abandoned the submarine and took to the water.”

The exact spot where the 283ft-long submarine sank in the Mediterranean Sea had remained a mystery for 70 years. That was until a marine archaeology survey team confirmed they had discovered the Olympus’ resting place using side-scan sonar to survey the seabed.

A year ago, the marine archaeology survey team from the Aurora Trust discovered the sub using side scan sonar. But at the time, they weren’t sure exactly what the image showed. The team, which operates from Malta, returned a few months later with deep-sea robotic vehicles to videotape the wreck − twice as deep as recreational divers can go.

Timmy Gambin, the archaeological director of Florida-based Aurora Trust, said: “Armed with our research on the features of the submarine, where the guns were, the placing and types of the rudder and propeller, we were able to identify her.

“Except for the damage from the mine she was in pristine condition, sitting upright as if she’d been placed on the seabed.”

Olympus is in the best condition of any wreck found by the Aurora Trust with almost no underwater growth on it.

“Sure enough, there was a submarine, sitting on the bottom, with the propeller intact and the hatch open,” said Ian Koblick, who co-founded the trust with fellow ocean explorer Craig Mullen in 2003. “We were pretty sure it was the Olympus because of the configuration of the [eight bow] torpedo tubes, the location and the fact that it was armed.”

The video shows cannons onboard, antennas for the radio, machine guns and a blowout at the bottom of the sub, where the mine struck, Koblick said.

The video also showed the distinctive feature of an Odin class sub: a 4-inch deck gun. It was found slightly elevated, looking ready for action.

Still, it took a few more months of further research before Malta’s Superintendent of Cultural Heritage was satisfied the submarine was indeed the Olympus.

In 2008, a team of technical divers from the United Kingdom and Malta claimed they had discovered the Olympus after identifying features that appeared consistent with the submarine’s layout. But their dive was brief with low visibility.

The technical divers said in a release three years ago they would return to positively identify the wreck, but they never did.

On Monday, Malta authorities gave the Aurora Trust permission to announce the discovery. “It took time because they are very protective of their cultural resources,” Koblick said according to the Miami Herald, which reported the story.

A trust executive notified the British Embassy in Washington about the submarine discovery on Tuesday. Plans are being made to show a British Navy Admiral the video footage and provide all information they have about the discovery.

The submarine is the likely resting place for at least a few of the military men who didn’t survive.

“It’s quite a sad story,” Koblick said. “These folks were on their way home via Gibraltar. Some had survived two other submarine sinkings.”

During the height of the Italian and German blockade of Malta, the British Navy battled to keep the island supplied with fuel, food and war supplies. Submarines played a key role.

The Olympus was launched in 1927 and served the Royal Australian Navy in China before being deployed to the Mediterranean to support allied efforts.

The trust’s operation has discovered 24 ancient shipwreck sites, many not seen for 2,000 years or more. It has also uncovered other World War II shipwrecks, more than a dozen World War II airplanes and unexploded military mines.

Timmy Gambin, the trust’s Maltese archaeologist, said three months ago that the team was mapping “the underwater landscape of war”.

The Olympus is the best-preserved World War II relic that the trust has found.

“It was like somebody took your toy submarine and put it on the bottom,” Koblick said. “There is hardly any growth.”

The trust is hoping to do a documentary about the discovery.

The site is due to be formally designated by the Commonwealth War Graves Commission and is being treated with “every sensitivity possible”, Mr Gambin said.