Harbour. Several of the city's suburbs, including Blackrock, Mahon, Douglas, Passage West and Rochestown lie on Lough Mahon or the Douglas Estuary, both of which are parts of Upper Cork Harbour. The Lower Harbour has a number of towns around its shores. Passage West, Monkstown, Ringaskiddy and the smaller village of Raffeen are found on the western shore. On the southwestern shore is Crosshaven. Great Island, which forms the northern shore of the lower harbour, houses the town of Cobh. As of 2011, Cobh had a population of about 12,500. The eastern shore is less densely populated, but has two villages Whitegate and Aghada, both home to power plants. The village of Ballinacurra is on the northeastern spur of the harbour, known as the Ballynacorra River. Due to the recent expansion of the town of Midleton, Ballinacurra has effectively become a suburb of Midleton, so it could also be said that Midleton lies on Cork Harbour. Military Cork Harbour hosts the headquarters of the Irish Naval Service. Prior to the transfer of the treaty ports in 1938, Cork Harbour was an important base for the British Royal Navy. Some of the first coastal defence fortifications built in Cork Harbour date to the 17th century, and were primarily intended to protect the approaches to Cork city. In the 18th century, fortifications were built on and opposite Haulbowline Island to protect the anchorage in Cobh - including Cove Fort (1743). Fort Camden and Fort Carlisle were built at opposite sides of the harbour entrance during the period of the American War of Independence. The harbour's military significance increased during the Napoleonic Wars, when the naval establishment in Kinsale was transferred to Cork Harbour. The harbour became an important anchorage, which could be used to guard the entrance to the English Channel and maintain the blockade of France. At this time, the naval dockyard on Haulbowline Island was constructed, as well as a fort on Spike Island (later to become Fort Westmoreland) and a number of Martello Towers and other fortifications were added or improved around the harbour. The fortifications were developed throughout the 19th century and a further fort, Fort Templebreedy, was added to the south of Fort Camden at the beginning of the 20th century. At the time of Irish independence, Cork Harbour was included, along with Berehaven and Lough Swilly, in a list of British naval establishments that would remain