It came down to three simple words in the end: "Paragraph Eleven; confirm".

It was a code, strung up in flags, but Admiral Ludwig von Reuter knew his men would understand the order.

They had been preparing for it for months.

It was June 21, 1919, and out in the brisk waters of Scapa Flow, the 74 warships under his command began to hoist the German flag one last time.

Hundreds of miles away, in Paris, the bitter wrangling over the peace treaty to officially end the Great War was reaching its height. The fate of the magnificent German warships was due to be decided.

The French and the Italians wanted some of the ships for themselves but the Americans did not approve and nor did the British.

Admiral von Reuter stood ready to take the decision out of their hands.

Those who knew him well described him as a gentleman, an exceptional officer with high conceptions of honour and duty. He did not want his fleet, already under British guard in the Orkney harbour, to be seized as spoils of war.

At 10:30am his own flagship, the Emden, sent out the command for his men to scuttle their own ships.

Seacocks, portholes, watertight doors, hatches and torpedo tubes were opened, and the German crews of around 2,000 men took to their lifeboats.

Swiftly, with a tremendous hissing of steam and gurgling water, the fleet began to sink beneath the waves.

It was the single greatest loss of shipping ever recorded in a single day.

The few British ships in the harbour desperately boarded some of the vessels to try to stop the scuttling, towing some of them into shallower waters or trying to force German sailors back onto their vessels.

The two sides came to blows, leaving nine German sailors killed and 16 wounded. It was to be the war's final death tally.

Within 24 hours the entire might of the German naval fleet would surrender out in open water to the British Royal Navy.

The last act of defiance from Admiral Ludwig von Reuter, however, would be remembered.

The graveyard of ships, lying broken on the sandy floor in the waters of Scapa Flow, a lasting reminder of history beneath the waves.

Today, the body of water in the Orkney islands known as Scapa Flow is still a natural harbour nearly 200ft deep in places.

The vast battleships that were scuttled there rest on the shallow sandy floor, and smaller blockships are dotted along the rugged coastline.

HMS Royal Oak and HMS Vanguard are war graves which must not be disturbed. Decorated now in anemones and plantlife, the flowers of the sea serve as living wreaths on the graves of the dead.

Nearby are the seven remaining warships of the German High Seas Fleet.

The wrecks of the SMS Cöln, SMS Kronprinz Wilhelm, SMS Brummer, SMS Karlsruhe, SMS König, SMS Markgraf and SMS Dresden all still lie where they sank off the coast of Orkney, almost a century ago.

The three battleships and four light cruisers have rusted and broken apart in the currents, but they still draw in visiting divers.

Most recently though, their visitors have been from a boat of intrepid men, all determined to help preserve the underwater monuments to the past.

The boat's skipper is Bob Anderson and his vessel contains an unusual mix of crew, including engineer and coastguard rescue officer Andrew Hunter, former probation officer Richard Booth, IT technician Alex Bicheno and Alex's dad, Pete.

Steve Jakeaway, an artist, is with them. He's a pretty major part of it. Together, they're trying to create a unique series of interactive maps, to help protect one of Scotland's most iconic shipwreck sites.

Seven ships, six men, and one groundbreaking goal to map the wrecks of Scapa Flow.

"Bob is a fairly adventurous guy," explains Andrew. "We'd been out at sea, talking about some of his projects, and he mentioned how he had an artist coming up who needed some divers."

So far, so simple. Bob and artist Steve intended to sketch out each sunken ship as accurately as possible.

The resulting maps would then help guide divers to explore the wrecks and serve as a way to highlight potential hazards.

Litter which divers spot such as discarded fishing nets are a constant problem, causing a phenomenon called "ghost fishing", when old nets get snagged and kill marine wildlife.

Scuba divers would be encouraged to log on-line any debris they spot on the wrecks on the maps. The data could then be recorded, gathered and prioritised, the items then uploaded to the list to be targeted for removal.

In a way, it would serve as an underwater crowd-sourced clean-up that could actively protect the wrecks over the years.

Andrew, the expedition leader, was eager to get involved.

"They're a bit of a diving mecca for divers," he says. "These wrecks are very old now but they're still pretty impressive.

"They have deteriorated but that is both good and bad - bad because you want to preserve them, good because as they fall apart, we can start to actually see inside them."

For an engineer whose mind lights up at mechanics, it's a veritable playground on the seafloor.

"Parts of it have opened up like a sardine can, and because the currents flow there is plenty of sealife, sea ferns and anemones growing on the wrecks," he says.

"When all these underwater flowers are open you can get some truly stunning vistas. You can see truly stunning images of magnificent ships as the natural daylight filters through.

"As an engineer I look at the way these great battleships were constructed and think how on earth would I have done that back then. It's intricate metal down in the turbines. It's all unique really."

What they needed was Steve to draw the shipwrecks, filling in as much detail as possible, to help both future divers navigate them and to provide a base for their interactive clean-up idea.

What Steve needed was every little detail you can only see when you're down at the bottom of the sea poking your head into a portal.

"He needed us to go down there and validate his drawings," says Andrew. "We have cameras, of course, and technology is advanced but it only does these ships so much justice."

The plan was Bob's diving boat, the Halton, an enthusiastic team of divers and copious cups of coffee.

All are members of the British Sub-Aqua Club (BSAC) which has a well established history of expedition diving. The club's current president is Prince William.

"We went down there, to the places where you can poke your head in and get a good look round," says Andrew.

"Then we'd pop back up to the surface, have a cup of coffee and a sit-down with Steve and tell him exactly what it looks like down there.

"I don't know if anyone has done something like this before."

The simple system worked well. Steve has been able to get into the fin ite, real-time details of the wrecks and the objects around them, from the ships' guns to fishing creels and discarded lines.

All seven wrecks have now been mapped, though several dives were needed on each wreck to produce an accurate illustration.

The map of the SMS Brummer, for example clearly shows the minelaying light cruiser submerged in the sea bed on its side. Green diamond symbols mark were debris has been removed, including three nets, two batteries, some buckie pots, rope and even two car tyres.

The map of the battleship the SMS Kronprinz Wilhelm shows red triangle symbols, marking where discarded buckie pots and rope have been spotted and are yet to be cleared.

"The idea was to create a series of very simple single-line illustrations showing the layout of each wreck so divers can easily work out what they are swimming over or under," says Steve.

"The Scapa Flow wrecks are all in between 12 and 45 metres of water, but the visibility is not always great," Steve adds.

"Often even experienced divers are not sure precisely what they are looking at, especially if a wreck has capsized and everything is upside-down."

The resulting drawings are being uploaded to the Big Scapa Clean Up project website which is run by Bob and Steve.

Bob, whose brainchild the Big Scapa Clean Up was, explains.

"The underlying concept is to protect our marine heritage," he says. "With these maps if we can not only document what is down there but also add some value, so that divers take a custodian role by logging what they see, then this encourages them to take more responsibility for protecting what is down there."

According to the team, the Karlsrhue is very broken up, but the Cöln is still intact. On the Kronprinz you can see a 12-inch gun that was fired at the Jutland, 36 metres down the gun barrels are still there.

The only other place you can see such guns is outside the British War Museum.

"This was my first time diving Scapa and it was absolutely excellent," says Alex.

"It's fascinating to think about what the lives of the people on board must have been like and imagine what must have happened in the moments before they sank."

One account that still exists today, is that of a young British officer, who recorded the dramatic events of that day in a letter to his mother.

Edward Hugh Markham David - Hugh, or "Ti" (short for "Tiny") to his family - was 18 years old in 1919, but had already been in the Royal Navy for two years.

His ship, the HMS Revenge had received a message at around 12:45 that day that its captive German ships were sinking. The fleet had turned back at full speed but it was too late.

"The sight that met our gaze as we rounded the Island of Flotta is absolutely indescribable," wrote David.

"A good half of the German fleet had already disappeared, the water was one mass of wreckage of every description, boats, carley floats, chairs, tables and human beings, and the Bayern the largest German battleship, her bow reared vertically out of the water was in the act of crashing finally bottomwards, which she did a few seconds later, in a cloud of smoke bursting her boilers as she went."

Admiral von Reuter was taken aboard HMS Revenge and David recounts, in great detail, the exchange between the two commanders.

"About the most dramatic moment of the whole day was the meeting of the English and German Admirals," wrote David.

"The two men were about the same height, both fine looking and tall. At first there was a pause, the German standing at the salute then the following conversation -

Fremantle: I presume you have come to surrender?

Von Reuter: I have come to surrender my men and myself (with a sweeping gesture towards the fast sinking ships) I have nudding else.

Pause

Von Reuter: I take upon myself the whole responsibility of this, it is nothing to do with my officers and men - they were acting under my orders.

Fremantle: I suppose you realise that by this act of treachery [hissing voice] by this act of base treachery you are no longer an interned enemy but my prisoner of war and as such will be treated.

Von Reuter: I understand perfectly.

Fremantle: I request you remain on the upper deck until I can dispose of you.

Von Reuter: May my Flag Lieutenant accompany me?

Fremantle: Yes, I grant you that.

David's account gives a rare insight into the tension on that day, and serves as another reminder to the current expedition crew as to why their work is important.

"It's been fascinating to dive on these wrecks," says Steve.

"The heritage of the area and the history of how they were sunk is unique and the project has given me a real insight into why they are an important part of our marine heritage.

"It's wonderful to be able to use our skills and expertise to help preserve something of real historic value."

While the maps are now up and available online for divers to use, the team's work is not yet over.

The crew plan to return this year with "more toys" to play with, particularly with the hope of creating 3D photo images of the wrecks.

"We're learning what works and what doesn't," admits Andrew. "It's a bit of a journey, but we're having a lot of fun doing it."

The goal is to help Bob and the rest of the Scapa Flow clean-up team get the shipwrecks and the area they rest in up to pristine condition as they mark a centenary since their sinking in June 2019.

The hope is that if enough care is taken of them now, they'll remain for another 100 years in the care of the harbour.

"We know they are not going to last forever," says Andrew. "But we have an obligation now to protect them as much as we can.

"We have phenomenal diving sites in Scotland and we need to protect them."

As team diver Richard adds: "When you are down there and you cast your mind back to when it was the most important naval base in the UK, people from all over the world come to dive there.

"It's important to preserve the history for future generations."

Underwater photos taken during dives on the German High Seas Fleet Big Scapa Clean Up

Admiral Ludwig von Reuter, the man who sank a navy, was made a prisoner of war after the events of that day, along with the other 1,773 officers and men of the fleet's remaining crews.

On his eventual return to Germany, he was requested to hand in his resignation from the navy.

He eventually became a State Councillor and wrote a book 'Scapa Flow: Grave of the German Fleet'.

In it, he described his thoughts leading up to the act that would destroy his entire fleet.

"Soon after the onward voyage to Scapa Flow," he wrote, "the feeling quickly came to dominate my mind that I should prepare a way out of internment worthy of the High Seas Fleet."

Reuter was later made a full Admiral in 1939 to celebrate the 25th anniversary of the Battle of Tannenberg.

He died in Germany of a heart attack on December 18, 1943.