The Firth of Clyde encloses the largest and deepest coastal waters in the British Isles, sheltered from the Atlantic Ocean by the Kintyre peninsula which encloses the outer firth in Argyll and Ayrshire, Scotland. The Kilbrannan Sound is a large arm of the Firth of Clyde, separating the Kintyre Peninsula from the Isle of Arran. Within the Firth of Clyde is another major island - the Isle of Bute. Given its strategic location, at the entrance to the middle/upper Clyde, Bute played a vitally important military (naval) role during World War II.