In 1914 the Royal Navy's Grand Fleet moved to a new base in Scapa Flow. They needed somewhere suitable to take on a German Fleet based in the Baltic and this atoll-like stretch of water, one of the largest sheltered harbours in the world, was ideal for the needs of the Admiralty.
On arrival the Navy found a wonderful harbour, but no defences at all in place. Approaches were rapidly defended, and steps taken to close the narrow passages between five islands on the eastern side of Scapa Flow by sinking blockships.
At the start of WWII the WWI defences were brought back into use and further blockships sunk. But they proved inadequate. On 14 October 1939, The German U-Boat, U-47, took advantage of a high tide to get past the blockships and into Scapa Flow. Once there, U-47 torpedoed HMS Royal Oak before leaving the way it had entered. 833 members of the Royal Oak's crew were killed.
Within a month, Winston Churchill visited Orkney and ordered that work begin on the construction of four permanent barriers linking together the chain of islands from Mainland in the north to South Ronaldsay in the south. The contract was given to Balfour Beatty and work began in May 1940.
The Churchill Barriers were formally opened by the first Lord of the Admiralty on 12 May 1945: ironically just in time for the war's end. As a result their lasting role was not as a defence for Scapa Flow, but as a series of causeways linking the five islands together.
The other lasting legacy of the building of the barriers came from the employment here of over 1300 Italian Prisoners of War, captured in North Africa. It is usually forgotten that 800 of these men were housed in camps on Burray. Much better known are the 550 who were housed in Camp 60, on the northern slopes of Lamb Holm.
Today the site of the camp is marked by a statue of St George constructed from barbed wire coated in concrete. And it is also marked by a true masterpiece, the Italian Chapel. This was constructed by prisoners to serve the camp, and remains a lasting monument to the prisoners and to the Orcadians who befriended them.
The total length of the four causeways was 9150 feet, or not far short of two miles. 40,000 cubic metres of rock was encased in wire cages and dropped into water up to 70 feet deep from overhead cableways. These were topped off with 300,000 tonnes of concrete blocks, the part of the structure most readily visible today. Material was quarried on Orkney, and concrete blocks were cast on an industrial scale on the islands before being brought to the cableways by a network of railways.
Today, the three most northerly barriers remain much as built, though the roads crossing them have been upgraded over the years. The most southerly, Churchill Barrier No 4, no longer looks artificial. Over the years dunes have accumulated on the eastern side and as a result Burray and South Ronaldsay are no longer really separate islands. Today the barriers, or more accurately the remaining blockships still in the channels either side of them, also provide an attraction for divers visiting Orkney.