Dr Innes McCartney was seated in his office in Bournemouth when the call first came through.

A nautical archaeologist, his number was pretty much on speed dial for most companies whose work involved rummaging around the seabed.

"We're a rare breed," he jokes, and sure enough the voice on the end of the line was from a major contractor he'd heard from several times before.

Scottish Power they said, marine engineers. They were off the coast of Scotland and thought they had found something.

The engineers had known there was something down there for a few years, before the £1bn project to lay one of the world's largest subsea power cables between Scotland and England, had begun.

It was September, the weather was already turning, but deep on the rocky floor beneath the turbulent Irish sea their sonar had picked up an unusual find.

Unusual finds are Dr McCartney's speciality. He's personally discovered close to 50 sunken submarines. "So I know what they look like," he jokes.

Which is why the images the engineers sent through made his archaeological senses tingle.

The scans showed a wreck, the watery grave site of a submarine, lost for a century but still intact.

There were at least 12 British and German submarines known to have sunk in the waters of the Irish Sea during World War One and Dr McCartney suspected this iron lady could be one of two known boats.

The first, boat UB-82, was sunk on April 17, 1918 by HMS Pilot Me and HMS Young Fred and it's recorded that 37 crew members died in the event.

The second, a sister boat to UB-82, was an altogether different story though - a submarine at the centre of one of the world's strangest naval war mysteries.

According to official records by the British Naval Department, UB-85 was hit by gunfire from the British patrol vessel HMS Coreopsis while attempting to dive. It resurfaced and was abandoned by her crew.

Every single unofficial account, however, says something entirely different and float around websites focusing on alleged paranormal events.

According to the old sea yarn, the submarine's captain, Günther Krech, explained to his bemused British captors that his vessel has been cruising on the surface because he could not dive, due to damage caused by "a strange beast" that leaped out of the water.

He told how the sub had been recharging batteries at night when a monster rose from the sea, a "beast" he said, 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.

The damage forced the entire crew to surrender to the British patrol: the men were taken off and the submarine scuttled.

While historians have been quick to point out the unlikelihood of a monster attack in the Irish Sea, one Scottish expert of a different kind is willing to consider a similar theory.

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

"The WWI report from the Captain of the British ship HMS Hilary a year earlier makes it clear that seafarers at that time were well aware of large sea 'monsters' that could be harmful to their ships."

As Gary says, history has shown consistent reports of large 'monsters' not just in lakes and lochs like Loch Ness but out in open waters as well.

"For many years the giant squid was known as the fearsome Kraken and given the size of the oceans, it wouldn't be a surprise if many large species were still to be discovered," he adds.

"The area of sea where the attack took place has a history of sea monster sightings - they have ranged from the north coast of Wales to Liverpool bay. What the German Captain said could well be true.

"It's great to see how Nessie's saltwater cousin clearly got involved in helping with the war effort - she even managed to do the damage without anyone being killed."

While Nessie spotters might be happy at the prospect of a distant Scottish cousin floating about the Irish Sea, historians like Dr McCartney are now waiting to see if any more identification comes through for the sunken sub to see which German lady, UB-82 or UB-85, currently lies beneath the surface.

"While I can conclude that this wreck is likely to be one or the other, they would be practically impossible to tell apart, aside from the numbers painted on them in service, now obviously long gone," says Dr McCartney.

"Unless a diver can find a shipyard stamp, we cannot say definitively but yes, we're certainly closer to solving the so-called mystery of UB-85 and the reason behind it's sinking - whether common mechanical failure or something that is less easily explained."

"After that though, I don't think there is really anything else left to do with it," he adds.

"Sometimes, with these things, it's better to leave them down there alone at rest."