A former coastal battery of 1888 on an artificial island, originating in a coastal battery structure of 1854, and operating as an outpost of Golden Hill Fort. The fort was altered during World War II, when it was used as an anti-shipping observation tower, and closed to military use in 1957. During the 1970s and 80s it was converted to luxury flats. The foundations and superstructure are of brick with a granite base, the later additions are in blockwork or concrete; all now rendered except for the western face. The original block is a broad regular chevron in plan and is of three storeys surmounted by a warhead. Above this is a lift shaft designed to serve a smaller fourth storey of flat-roofed buildings constructed for anti-aircraft purposes. The granite base shows a descending sequence of housings for the sleepers of the Brennan torpedo launch rail, now dismantled. It was intended to house 29 guns in four tiers, being among the last gun-towers constructed in England, but was rapidly rendered obsolete by advances in gunnery. In 1886 it was chosen as one of the UK locations for the Brennan wire-guided torpedo which had a range sufficient to close the strait. This too became obsolete, and was dismantled in 1906. Thereafter small guns only were mounted on the fort. The fort is architecturally important as a late example of its type, and historically important for having housed the former Brennan installation.