Photos show the recently discovered wreck of a World War II-era submarine more than 80 years after a German sub sank it

• Researchers discovered the wreck of a World War II-era submarine off the coast of Norway this year.
• The HMS Thistle was a British sub that sank after being hit by a German vessel in 1940.

A crew of Norwegian maritime researchers said they stumbled upon the long-lost wreck of a World War II-era British submarine that was torpedoed by a German submarine in 1940 just seven months after the war began.

Researchers with Norway's Institute of of Marine Research and the MAREANO program, which maps seabed biology and geology, discovered the wreck's remains earlier this year, according to a press release from the Institute of Marine Research.

But it took until this fall for researchers to confirm the wreck was the HMS Thistle, a British Royal Navy submarine that sunk off the coast of Norway in April of 1940 after being hit by a German submarine. The strike resulted in the deaths of all 53 crew members.

Researchers on board a routine cruise earlier this year noticed peculiarities on their map, according to the Institute of Marine Research. Unaware of whether the abnormalities were part of the seafloor geology or something else, the crew established a research station to investigate further.

An underwater camera eventually revealed the remains of a submarine sitting more than 500 feet beneath the ocean's surface, outside Rogaland, Norway, the press release said.

"Since there was no sign of any wreck right here, I checked if there were any submarines that were missing in the area and that could match this wreck," senior engineer Kjell Bakkeplass told the Institute for Marine Research.

Researchers consulted with both the Norwegian and British navies before confirming the submarine was a lost British vessel. They eventually narrowed it down to one of two options: the HMS Oxley, which was accidentally sunk by another British submarine just seven days after WWII began, or the HMS Thistle, which was hit by a German submarine in April 1940.

Historic information suggested the Oxley was the closest geographic wreck to the site, Bakkeplass said, but offshore submarine experts eventually determined the wreck was likelier to be that of the Thistle.

"After several people had studied the photo, we concluded that it was probably HMS Thistle, but the photo showed too few details for it to be conclusively settled," Bakkeplass said.

A second exhibition in October passed by the wreck again and confirmed this time that the wreck was the Thistle, the Institute for Marine Research said, though the British Royal Navy maintains rights of ownership over the underwater grave and has final say on identifying the submarine.

The Royal Navy did not immediately respond to Insider's request for comment.

Bakkeplass said the assumed position of the Thistle was likely wrong for years because of the vessel's antiquated bearings.