How castles served as Second World War coastal defences

Were castles commonly used for coastal defence during the Second World War?

Existing castles were often adapted when their locations were useful, but modern coastal defence relied mainly on purpose-built forts, batteries, and beach defences.

Existing masonry sites mattered chiefly because they already occupied defensible coastal positions. The panel distinguishes a residential castle from a purpose-built fort while noting that the line blurs when an old castle is militarized. German adaptations in Jersey show how an established site could be reused. Singapore, Fort Drum, the Atlantic Wall, and substantial British works show that modern defence still depended mainly on purpose-built forts, batteries, and beach positions.