IT has lain on the bottom of the seabed off the Scottish coast for almost a century after an encounter with a British warship and, its captain claimed, a sea monster.

But now fresh light could be shone on one of the First World War's most enduring mysteries after engineers discovered what may be the watery grave of submarine UB-85.

Marine engineers working on the Western Link project, a joint venture between ScottishPower and National Grid to lay an undersea electricity cable between Scotland and England, pinpointed the wreck while surveying the sea bed off the coast of Dumfriesshire.

Remarkable sonar images show the 100-year-old vessel largely intact and attempts to identify it have led experts to conclude that it may be that of UB-85.

The German warship was sunk in April 1918 after it was caught on the surface during the day by a British patrol boat. The German submarine crew surrendered without resistance, to the surprise of their British counterparts.

However, another story has long been associated with the U-boat and its commander, Captain Krech. An old sea tale, widely shared online, recounts that the Captain, when questioned about why he had been cruising on the surface, told how the sub had been recharging batteries at night when a "strange beast" rose from the sea.

He is said to have described a "beast” with “large eyes, set in a horny sort of skull. It had a small head, but with teeth that could be seen glistening in the moonlight".

The animal was so large that it is claimed it forced the U-boat to list greatly to starboard. “Every man on watch began firing a sidearm at the beast," Krech is believed to have said, telling how the battle continued until the animal dropped back into the sea.

In the struggle, though, the forward deck plating had been damaged and the sub could no longer submerge. "That is why you were able to catch us on the surface," the Captain is said to have concluded.

Innes McCartney, a historian and nautical archaeologist who has been working with the Western Link team in a bid to identify the wreck, said that the mystery of UB-85 could be one step closer to being solved.

Monster hunters say that an examination of the wreck may also shed light on its supposed encounter with an unidentified beast from the sea.

Gary Campbell, keeper of the Official Sightings Register of the Loch Ness Monster, said: “It is entirely feasible that some large sea creature disabled the submarine.

"History has shown that there have been consistent reports of large ‘monsters’ not just in lakes and lochs like Loch Ness but out in open waters as well."

Peter Roper, of Western Link partner ScottishPower, said: “The images we get back from the subsea scans are incredibly detailed, but we obviously need to be aware of what lies beneath before we can start laying a power cable. In all the years I have been building power lines, I can say that this is the most extraordinary discovery."