THEY lie deep in the murky waters of the Forth, trapped on the seabed, rusting treasure troves of mine-blasted boats and tragic fishing trawlers.
There are early 20th century steamers which carried coal and food up and down the Firth of Forth, warships scuppered in the heat of battle, schooners lashed by gales, submarines, even a one time luxury liner, a tanker and a clutch of unfortunate planes.
Wrecks in the Forth: Click here to open PDF map showing sites of lost vessels
And somewhere – but no-one is certain where – lies the Blessing of Burntisland, believed to be still laden with its royal golden treasures, the kind of multimillion pound bounty any diver worth his sea salt dreams of finding.
Which might be why Scottish Government ministers have launched their own maritime manoeuvres aimed at protecting the country's shipwrecks.
The proposed Scottish Marine Bill will record and safeguard shipwreck sites throughout Scottish waters, increasing the range of marine sites that may be listed as being of "national importance" and throwing an exclusion net around some which might be of particular historic significance.
Around 500 wrecks are believed to litter the bed of the Firth of Forth – from the Kitty just off Dunbar, a 105ft trawler blown up by a submarine in 1917, to the glittering prize of the Blessing. And while diving school boss Mark Blyth says they may not harbour pots of gold, they do boast plenty of interesting features.
"There are a lot of wrecks out there, some are very scenic and very colourful, often covered in soft corals which makes them really impressive," he says. "People imagine it's very murky and dull down there – it isn't."
The wreck many divers want to see is that of the Campania, a one-time luxury Cunard liner recommissioned by the Royal Navy during the First World War.
"At one time it held the Blue Ribband for crossing the Atlantic," says Mike, of Dive Bunker, based in Burntisland. "It was supposed to be scrapped then the Navy had it turned into an aircraft carrier. But it became stuck after a storm in 1918 when it dragged its anchor just off Burntisland. It hit HMS Revenge and the Royal Oak before it went down.
"You're captured by the sheer size of the structure – it was the largest ship to sink in the Forth – even though it was eventually blown up and anything of any worth salvaged."
On a calm summer day, visibility can stretch to 15 to 20 metres, but even seven or eight metres visibility offers divers like Mark an opportunity to find things they might have missed on previous dives.
Such as the time he explored the wreck of the Royal Archer, a steamship blown up by a mine in 1940 around five miles off Kirkcaldy, only to find the "holy grail" of shipwreck treasure for local divers.
"We'd dived before but hadn't seen anything of great note," he recalls. "Then we came across the ship's bell which was an incredible find."
He laughs off suggestions that his next find might be the treasure of the Blessing of Burntisland. He was involved in searches several years ago that failed to confirm the historic vessel's resting place. However, he did find another remarkable piece of seabed booty: the crumpled wreckage of a plane.
"It was around the time there was a lot of excitement over the Blessing. Prince Andrew was on a ship that did a sweep and spotted something.
"I went down thinking I was going to find a tug, instead I found myself sitting in the cockpit."
The plane turned out to be the remains of a German Avenger torpedo bomber. It had been based at 785 Squadron at Crail, suffered engine failure and ditched during a training flight in December 1945.
Perhaps the most poignant dive for Forth explorers is the one to the watery grave of the English-based armed tug, HMS Saucy.
Just 155ft in length, she was working in the vital role of mine clearance in September 1940 when she disappeared only ten minutes after setting off.
Twenty-eight people on board – many from the same families in Brixham, Devon – perished, making it the Forth's worst maritime disaster.
"There are people who dive it without knowing much about its history who talk of feeling a certain kind of electricity when they are there. They've surfaced and asked right away 'did anyone die on there?' It's not something I've encountered, but there does seem to be a kind of energy around it," says Mark.
Wrecks are still being recovered – but as yet they don't include the Blessing of Burntisland, sunk in 1633 during a vicious storm with King Charles I's personal cargo, 30 courtiers and servants on board along with a royal heirlooms valued at 500 million today.
However, in 1997 engineers working on the foundations of the Forth Road Bridge found the century-old wreck of the Telesilla.
It's the unpredictability of the Forth wrecks that keeps divers returning, says Mark. "I dived in Tenerife recently and within a few days I was bored. Diving in the Forth you are always finding things.
"However, divers these days are very aware of preservation and the environment – they are more likely to take photographs than take anything from a wreck."
However, Philip Robertson, Historic Scotland's senior inspector of marine archaeology, believes there is a need to reform shipwreck laws. "The existing laws are widely considered ineffective," he says. "Proposals for new legislation would give us a more effective and workable tool to safeguard marine sites."
Gary Lawson of Dunbar-based Dive Safari believes moves to slap protection orders on wrecks wrongly suggests divers are underwater vandals.
"Do they really think that divers go off with a hammer looking to batter bits off wrecks to take home and stick in the garage? The divers I know are professional, responsible people.
"They are certainly not vandals."
And as for precious gems and gold bars lurking below the waves, Mark insists they don't exist – or if they do, he's not found them.
"I did find something else, though," he smiles. "When I was sitting in that ditched plane, I looked over on to the wing and there was a set of false teeth. Not exactly treasure from the deep!"