The Flat Holm Coastal and Anti-Aircraft Defences consist of two pairs of dual-purpose anit-aircraft and anti-shipping gun emplacements, which date to the mid and later periods (1941-45) of World War Two. Both the South Battery and the North Battery comprise a pair of gun emplacements, a command post, magazine and a pair of coastal artillery searchlight emplacements. Both batteries shared a common radar receiver platform. The structures formed part of the Fixed Defences, Severn scheme and protected the Atlantic shipping convoy de-grouping zone between Cardiff, Barry and Flat Holm. The structures were made up of combinations of brick, reinforced concrete and hollow concrete brick, with many of them being part buried in to the ground surface and/or surrounded by an external bund of earth and stone.
Source: Cadw scheduling description, January 2008.