With the Devonport Lines protecting the Dockyard from landward attack, Mount Wise provided the key vantage point for defending against an attack from the sea. An octagonal redoubt with stone walls was built on Mount Wise in the 1770s, forming an emplacement designed to house guns for the purpose of defending the Royal Dockyard. In 1806 a semaphore signalling station was built within it, the last of a series of 32 linking Plymouth with the Admiralty in London. In the 1960s much of the structure was demolished, but many relics survive such as the external walls, semi-circular metal racer rails for the guns, World War II barage balloon anchoring rings, ammunition recesses and iron rings for manoeuvring the heavy guns. In 1998 a mast was built, with circular viewing platform for recreational use by visitors, giving panoramic views, most notably westward to the Royal William Yard.
