Scapa Flow (/ˈskɑːpə, ˈskæpə/; from Old Norse Skalpaflói 'bay of the long isthmus') is a body of water in the Orkney Islands, Scotland, sheltered by the islands of Mainland, Graemsay, Burray, South Ronaldsay and Hoy. Its sheltered waters have played an important role in travel, trade and conflict throughout the centuries. Vikings anchored their longships in Scapa Flow more than a thousand years ago. It was the United Kingdom's chief naval base during the First and Second World Wars, but the facility was closed in 1956.