THE captain of U-boat 47 was nervous as his vessel slithered and squirmed its way between the anti-submarine nets and sunken ships designed to block off entrance to Scapa Flow.

At one stage his vessel had got stuck and was trapped in the headlights of a car on a nearby headland.

Fortunately its driver was more interested in relieving himself after a few jars in a local dance hall and the Germans' luck held.

Soon after gaining entrance to the inland sea, the imposing shape of battleship HMS Royal Oak loomed into view.

The anxiety of their desperate mission affected the U-boat's crew and the vessel's first salvo of torpedoes missed the moored ship, although one struck the anchor chain and gave the vessel a good rattling.

It is said that of the crew of 1,400, those who left their bunks to find out what had happened were the ones who survived the rapid sinking. With its next salvo U-47 blew a giant hole in Royal Oak's hull and the ship took over 800 sailors to a watery grave.

The site, visible from the road between Stromness and Kirkwall, is now an official war grave. It's a contributor to the huge naval history which this small set of islands could boast.

But boasting is not the Orcadian way: the community of 20,000 souls, outnumbered by their sheep and Aberdeen Angus cattle, keeps its knowledge on the inside and quietly turns its hands to whatever living it can make.

In recent years one of its best prospects has been salmon farming. Unlike the West Coast of Scotland, Scapa Flow has a vigorous current surging and foaming through its mass.

It may make feeding time a hair-raising experience for staff on wilder days, but it can scour any salmon pen and force its inhabitants to swim against the current, creating fine, muscular physiques.

Salmon farming in tamer waters has been beset by problems with disease and infestations of sea lice. This in turn has led to chemical treatments and pollution.

But find the right site and practice the right husbandry and it appears possible to avoid most problems. The salmon I saw in Mainstream's non-organic pens had no lice and had not been treated for it.

Another Orkney playing card is its lack of salmon rivers, which neatly avoids the confusion that can arise if escaped salmon try ascending river courses without the genetics that tell them what to do.

It was this combination of factors which led Waitrose fish obsessive Jeremy Langley to the Orkneys four years ago.

He wanted to work with local producers to develop the best quality farmed salmon in the world. To do this, he committed supermarket heresy and entered into long-term working partnerships with suppliers Aquascot and Mainstream. This gave them the confidence to invest in the future.

The cast of characters now involved in producing Waitrose Select Farm Salmon is so vivid it should be in a film.

Take Dennis Overton of Aquascot, for example, a tall, laconic agriculture specialist who is calmly plotting a sustainable future for the industry. In his terms this means one in which every partner in the chain - suppliers, supermarket, environment, local community, "and most importantly the fish" - are beneficiaries.

And then there's Michael Tait from the adjacent Shetland Islands, marine biologist and son of one of the early fish farmers.

Mr Tait manages Mainstream's salmon farming sites across the Orkneys and Shetlands. The winds which rake the islands must be getting to him, last week he proposed to his girlfriend.

He described the massive amount of work which has gone into developing the fish pellets. You are what you eat, as the saying goes and the same is true for the salmon.

Mainstream's product is made locally with all-natural ingredients and comes in a range of sizes to suit smolts (baby fish) to ravenous adults. "We have to change the pellet size gradually. Fish are very boring they want the same thing every day."

He's assisted by colleague Ann-Marie Charleson, fellow scientist and former lecturer who has just become the company's operations director.

The Orkney site manager is Andy McLaren, a man who relocated from the English south coast 20 years ago with his boat and diving gear.

Prior to salmon farming he made a living diving for fruits of the sea like scallops and when they were out of season for the thousands of tons of steam coal lying on the bed of Scapa Flow.

At the end of the First World War the 70 interned ships of the German battle fleet scuppered themselves in the Flow.

A resourceful scrap merchant by the name of Cox salvaged most of them by pumping air into their hulls and floating them upside down to a Scottish breaker's yard. Their huge coal stocks were left on the ocean floor and it burns as well today as it did in 1918.

The salmon pens are clustered in groups of eight to ten in bays around the Orkneys. Each holds from 10,000 to 20,000 fish in various states of maturity up to their harvesting age of about two years. By this time they're strong, vigorous fish weighing 10 to 12 pounds.

The salmon have to be protected from their greatest predator, the seal, by a high frequency bleeper attached to the pens.

Mr Tait said: "Left unprotected a seal will 'punch' into the pen's net and bite out the salmon's liver and other vital organs."

Nursing a tender up to a pen and engaging the blower to throw in tons of fish pellets can be a challenge in a big swell but it's nothing compared to the challenge of Mainstream's environmental director Robin Miller.

A surgeon's son from Edinburgh who skipped medical school for environmental science, Mr Miller has to reconcile a commercial operation with some of the most extensive and stringent regulation in the world. He claims the amount of legislation affecting salmon farming is almost incalculable as so many bodies have an interest.

"Applying for planning permission to move the pens a short distance can take a couple of years," he said.

Fortunately, the Waitrose Select farm scheme has been constructed to anticipate and surmount the issues and fears that are part and parcel of a young industry.

Jeremy Langley understands these issues. He's a fish buyer whose holidays consist of sea-fishing trips where he wears the skin off his thumbs arresting his fishing line as the bait plummets to the ocean floor. "What do you think of the operation?" He asked me. "I'm so close to it after four years' work I'm not sure how it looks to an outsider. But I love fish and I want my kids to enjoy them too. That's why we have to build a sustainable industry."