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.

The River Clyde is a river that flows into the Firth of Clyde in Scotland. It is the ninth-longest river in the United Kingdom, and the second or third longest in Scotland. It runs through the major city of Glasgow. Historically, it was important to the British Empire because of its role in shipbuilding and trade. To the Romans, it was Clota, and in the early medieval Cumbric language, it was known as Clud or Clut. It was central to the Kingdom of Strathclyde.