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After 80 years of debate about its existence, researchers have discovered the remains of a 30ft monster deep under the waters of Loch Ness.

Some have long believed that seawater must have entered the loch after the last ice age and that was how Nessie got in.

But what has been found by a new underwater sonar-imaging investigation is of more recent origin, having been a model from the 1970 film, The Private Life of Sherlock Holmes.

It was directed by Billy Wilder and starred Robert Stephens and Christopher Lee. It is thought the model sank after its humps, which made it buoyant, were removed. It has never been seen again, until now. The monster was actually a submarine in the original movie, although Dr Watson apparently made his own sighting of Nessie.

Norwegian company Kongsberg Maritime, experts in subsea survey and construction, is using its torpedo-shaped Munin device or drone to conduct the most technologically advanced examination of Loch Ness, yet undertaken

Normally used to trace ships, equipment or aircraft lost at sea, it is equipped with sonar imaging to survey the bottom of the loch which is over 750 feet deep in parts.

Supported by The Loch Ness Project and VisitScotland, the state-of-the-art marine robot, has already revealed other new information about the loch.

Claims made in January that a ‘Nessie trench’ had been found in the northern basin of the loch are incorrect, according to Munin's more precise data.

Meanwhile a 27-foot long shipwreck has also been uncovered at the bottom of the loch and the team is tracing the origins of the boat.

The survey, the first of its kind in Scotland, is being carried out over two weeks by Kongsberg, with an analysis of findings and discoveries every day. Loch Ness has been notoriously difficult to survey in the past due to its depth and steeply sloping side ‘walls’ consisting of hard clay and rocky outcrops.

Operating autonomously, the device is over 13 feet long.

Discoveries previously made in the loch over the years include: a crashed Wellington bomber from the Second World War, a 100-year-old Zulu class sailing fishing vessel and parts of John Cobb’s speed record attempt craft Crusader which crashed at over 200mph in 1952.

It is estimated that the Loch Ness Monster or ‘Nessie’ phenomenon is worth more than £60 million to the Scottish economy drawing visitors from around the world.

Craig Wallace, Subsea Applications Engineer, Kongsberg Maritime said:

“Kongsberg first surveyed Loch Ness with some of the world’s first multi-beam sonar back in 1987 and have continually visited bringing the latest technology to uncover this loch’s mysteries.

“Munin is the most advanced low logistic autonomous underwater vehicle (AUV) in the world and is the first in the next generation AUVs from Kongsberg Maritime. The vehicle allows sonars to scan just a few metres from the loch floor, giving resolution several orders of magnitude greater than anything before.”

Adrian Shine, Leader of the Loch Ness Project, said:

“Because Munin can dive and navigate itself safely at great depth, it can approach features of interest and image them at extremely high resolution. We already have superb images of the hitherto difficult side wall topography and look forward to discovering artifacts symbolic of the human history of the area.”

Malcolm Roughead, Chief Executive of VisitScotland said: "We are excited about the findings from this in-depth survey by Kongsberg, but no matter how state-of-the-art the equipment is, and no matter what it reveals, there will always be a sense of mystery and the unknown around what really lies beneath Loch Ness.”