The castle was brought back into use in the Second World War by the British Southern Command to defend the coast against German attack. In June 1940 it was re-equipped as a gun battery and observation post, with additional concrete defences laid around the position. Two naval guns were installed in one of the 19th century firing positions and in a new gun position built to the west of the castle; these were supplemented by a French gun, and the old blockhouse itself was used to control a minefield in the estuary below. The guns were manned first by the 364 Coast Battery of the Royal Artillery and then by the 379 Battery of the 557 Coast Regiment, but the battery was retired from active operations in November 1943. After 1945 the entire fort was decommissioned and the newer defences removed.