 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 4 @.@ 7 @-@ inch ( 120 mm ) naval guns were installed in one of the 19th century firing positions and in a new gun position built 50 metres ( 160 ft ) to the west of the castle ; these were supplemented by a French 75 @-@ millimetre ( 3 @.@ 0 in ) 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 . 
