. . "They were used by the Luftwaffe to defend against Allied air raids on these cities during World War II. They also served as air-raid shelters for tens of thousands of people and to coordinate air defence."@en . . . . "They were used by the Luftwaffe to defend against Allied air raids on these cities during World War II. They also served as air-raid shelters for tens of thousands of people and to coordinate air defence."@en . . . . . "Flak tower"@en . . . . . .