A sea loch which flows south to open onto the Firth of Clyde, the Gare Loch is located 13 miles (21 km) northwest of Glasgow. The loch is 7 miles (11 km) in length and 1 mile (1.5 km) in width. It is separated from Loch Long to the west by the Rosneath Peninsula. The town of Helensburgh lies at its mouth, Greenock lies opposite and around the loch are the villages of Rhu, Shandon, Faslane, Garelochhead, Clynder and Rosneath.
The deep water of Gare Loch has been associated with the navy since World War II, when a major base was developed at Rosneath and used by the Americans to train for landings in North Africa and on D-Day. In the 1950s British battleships were mothballed in the loch and by the 1960s it became the principal base for the UK's submarine-borne nuclear deterrent. Trident submarines remain berthed at HM Naval Base Clyde (Faslane), the locus for regular peace protests.