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The Churchill Barriers are a series of four causeways in Orkney, Scotland, with a total length of 1.5 miles (2.4 km). They link the Mainland in the north to South Ronaldsay, via Burray, and the two smaller islands of Lamb Holm and Glimps Holm.
On 14 October 1939, the Royal Navy battleship HMS Royal Oak was sunk at her moorings within the natural harbour of Scapa Flow by the German U-boat U-47. Shortly before midnight on 13 October U-47, under the command of Günther Prien, entered Scapa Flow through Kirk Sound between Lamb Holm and the Orkney Mainland. Although the shallow eastern passages had been secured with measures including sunken block ships, booms and anti-submarine nets, Prien was able to navigate the U-47 around the obstructions at high tide. He launched a torpedo attack on the battleship while it was at anchor in Scapa Flow. The U-47 then escaped seaward using the same channel by navigating between the block ships.
In response, First Lord of the Admiralty Winston Churchill ordered the construction of several permanent barriers to prevent any further attacks. Work began in May 1940 and was completed by September 1944. The barriers were officially opened on 12 May 1945, four days after the end of World War II in Europe.
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The contract for building the barriers was awarded to Balfour Beatty, although part of the southernmost barrier (between Burray and South Ronaldsay) was sub-contracted to William Tawse & Co. The first Resident Superintending Civil Engineer was E K Adamson, succeeded in 1942 by G Gordon Nicol.
The bases of the barriers were built from gabions enclosing 250,000 tons of broken rock from quarries on Orkney. The gabions were dropped into place from overhead cableways into waters up to 59 feet deep. The bases were then covered with 66,000 locally cast concrete blocks in five-ton and ten-ton sizes. The five-ton blocks were laid on the core, and the ten-ton blocks were arranged on the sides in a random pattern to act as wave-breaks.
A project of this size required a substantial labour force, which peaked in 1943 at over 2,000.
Much of the labour was provided by over 1,300 Italian prisoners of war who had been captured in the North African Campaign, and were transported to Orkney from early 1942 onwards. As the use of POW labour for war effort works is prohibited under the Geneva Conventions, the works were justified as "improvements to communications" to the southern Orkney Islands.
The prisoners were accommodated in three camps, 600 at Camp 60 on Lamb Holm and the remaining 700 at two camps on Burray. Those at Camp 60 built the ornate Italian Chapel which survives and has become a tourist attraction.