This group of forts was built near the Thames estuary for anti-aircraft defense and made up of several towers north of Herne Bay 9.2 mi (8.0 nmi; 14.8 km) from the nearest land. One of the seven towers collapsed in 1963 when fog caused the ship Ribersborg to stray off course and collide with one of towers. In 1964, the Port of London Authority placed wind and tide monitoring equipment on the Shivering Sands searchlight tower, which was isolated from the rest of the fort by the demolished tower. This relayed data to the mainland via a radio link. In August and September 2005, artist Stephen Turner spent six weeks living alone in the searchlight tower of the Shivering Sands Fort in what he described as “an artistic exploration of isolation, investigating how one’s experience of time changes in isolation, and what creative contemplation means in a 21st-century context”.