A shy hotel manager's fleeting glimpse of something strange in 1933 helped to create a modern monster myth. In 1987, the BBC reported on the scientists who used sonar equipment to search for Nessie.

The mystery of the Loch Ness Monster has puzzled scientists and delighted tourists for decades. A long thin lake in the Scottish Highlands, Loch Ness holds more water than all English and Welsh lakes together. Who knows what secrets may lie within its mysterious depths? From big-game hunters to trombonists seeking to coax the beast by mimicking a mating call, experts and amateurs alike have poured their hearts into capturing the elusive creature affectionately nicknamed Nessie.

In 1987, a major sonar exploration attempted to find out definitively if the Loch Ness Monster existed. The world's media descended on the tranquil grouse moors around the loch – the Scottish word for lake – for the launch of Operation Deepscan. An international team of would-be monster hunters turned up with £1m ($1.35m) worth of high-tech equipment, aiming to leave Nessie with no hiding place.

Twenty-four boats lined up to span the loch, each armed with cutting-edge sonar that cast a wall of sound down to the depths. Along its 23 miles (37km), the fleet trawled its sonic net through the water, as scientists scanned their charts for any telltale blips. No monster was found. Over the course of a week, however, the sensors did pick up three sonar contacts that indicated something big in the waters below the ruins of Urquhart Castle. And although that something could just have been a seal or a school of salmon, the good news was that it allowed the Loch Ness Monster myth to survive intact.

Project leader and veteran Nessie hunter Adrian Shine told the BBC: "I think if we were to get a fish on the scale that the contacts would suggest then I don't think anyone would be too dissatisfied, and all those eyewitnesses would get their vindication."

The mission's success was seen as inconclusive – "not proven", as Scots law might say. Sonar expert Darrell Lowrance certainly hedged his bets: "That doesn't mean there's a monster here, but it doesn't mean also that I suppose that there is not. I wouldn't want to be lynched in northern Scotland." Tourists were unfazed. One woman insisted she had "distinctly" seen the Monster during her visit. As the BBC's Clive Ferguson concluded: "If nothing else, Operation Deepscan has proved one thing; you cannot kill a legend with science."

The original Nessie legend dates to the 6th Century, when the medieval Irish monk St Columba is said to have encountered a creature in the River Ness, which flows from the loch. The modern monster myth began in 1933 with a rather reluctant eyewitness. One sunny spring day, hotel manager Aldie Mackay spotted something unusual in the water. It wasn't until 50 years later that she chose to give her first radio interview, on the........

© BBC