Flak towers were large, above-ground, anti-aircraft gun blockhouse towers constructed by Nazi Germany. There were 8 flak tower complexes in the cities of Berlin (3), Hamburg (2), and Vienna (3) from 1940 onwards. Other cities that used flak towers included Stuttgart and Frankfurt. Smaller single-purpose flak towers were built at key outlying German strongpoints, such as at Angers in France, Helgoland in Germany.
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