U.S. Department of War

“Those buildings which have been allowed to stand near the beaches have been incorporated in the defenses. Many attractive villas are still deceptively innocent and peaceful in appearance, but only the exteriors remain the same. The interiors have been converted into steel-and-concrete emplacements, and they have been armed with guns of varying sizes. Many of the houses have not been fortified so elaborately, but have been turned into effective positions for smaller guns and machine guns by the filling-in of doors and windows with brick or concrete. Passages have been cut through continuous rows of fortified houses so that the occupying troops may pass from one to another without being exposed to observation and fire from the beach.”
― U.S. Department of War, German Coastal Defenses