The latter were subsequently updated with longer-range coastal artillery - to support the naval defence of the "Western Approaches" during the First World War (early 20th century).
Some of these defences were tested during the Siege of Cork (1690) and Fenian Rising (1867) - the harbour remains the home-port of the Irish Naval Service.
Though declining in importance (relative to those at Cork Harbour) in the 18th and 19th centuries, several structures were in use until they were burned during the Irish Civil War (1922).
The deep-water berths at Bantry Bay and Berehaven Harbour were important from as early as the Nine Years' War and Siege of Dunboy in 1602, through the United Irishmen Rebellion and French Armada landings in the 1790s.
The defences at Baltimore, Roaring Water Bay and surrounding islands were largely built by landed families from the 14th to 17th centuries.