In response to the threat posed by France during the Napoleonic Wars, Lieutenant Colonel John Brown surveyed the castle in 1804 to examine whether the central keep could be turned into a Martello tower, a type of circular gun tower popular during this period. The scheme was not taken forward, although the defences of the surrounding coast line were much improved by the government. The painter J. M. W. Turner visited between 1805 and 1807 during the middle of this work, later depicting the castle in landscape paintings and sketches of the area.