The Drop Redoubt was a key element of the Western Heights fortifications. An Observation Post with integral shelter, of Second World War date, is set into the top of the magazine mound. Its position is indicated on a wartime plan when it was an artillery observation post. The square observation pit is approached along a brick-lined passage, 0.65m wide, down a flight of five steps; it comprises a brick chamber 2.45m square by 1.5m deep with a flat concrete floor. In the centre is a concrete pedestal, 0.3m in diameter by 1.5m high, onto which an optical instrument was mounted (although it resembles a mounting for a LightAAgun). Attached to the eastern side of the pit, reached down three steps, is a brick shelter, 2.43m by 1.24m, with a sloping concrete roof and a flat concrete floor. Ahole in the roof in one corner was possibly from a stove, and there are remains of a brick parapet wall along the front of the roof. Also on the magazine mound, slightly north of the OP, are the brick foundations of another small structure. It measures 2.19m by 1.30m internally, sunk at least 0.4m into the mound, with a small recess on the north side which measures 0.75m by 0.37m. Its purpose is unknown but may be part of an AA gun position known to have been in the Drop Redoubt during the First World War. (location accurate to the neares 1m based on available information)