The Firth of Clyde is the mouth of the River Clyde. It is located on the west coast of Scotland and constitutes the deepest coastal waters in the British Isles. The firth is sheltered from the Atlantic Ocean by the Kintyre peninsula, which encloses the outer firth in Argyll and Ayrshire. 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 and upper Clyde, Bute played a vital naval military role during World War II.

Ayrshire is a historic county and registration county, in south-west Scotland, located on the shores of the Firth of Clyde. The lieutenancy area of Ayrshire and Arran covers the entirety of the historic county as well as the island of Arran, formerly part of the historic county of Buteshire. Its principal towns include Ayr, Kilmarnock and Irvine and it borders the counties of Renfrewshire and Lanarkshire to the north-east, Dumfriesshire to the south-east, and Kirkcudbrightshire and Wigtownshire to the south. Like many other counties of Scotland, it currently has no administrative function, instead being sub-divided into the council areas of East Ayrshire, North Ayrshire and South Ayrshire. It has a population of approximately 366,800.