Nazi Flak tower. Used against allied aircraft in Europe. They had an air defense range of 14km and could put up 8,000 rounds in a minute!!!
10 Abandoned Gun Emplacements, Artillery Batteries and Flak Towers
The 350-strong garrison of the Zoo flak tower finally left the building. There was sporadic fighting in a few isolated buildings where some SS troops still refused to surrender, but the Soviets reduced such buildings to rubble.
Berlin WW2 German flak tower - there were three of these giants in Berlin,the Soviet tank guns could not dent them. They held thousands of Berliners and were surrendered at war's end.
The demolition of Berlin’s Zoo flak tower, known in german as the Flakturm Tiergarten, Zoo Tower.
Flak Tower Hamburg - well served its purpose, better to hid....
luftwaffe flak tower - Google Search
WW2 Bunkers-The Subject Of Contemporary Controversies And Urban Conversions - http://www.295luv.com/home-design/ww2-bunkers-the-subject-of-contemporary-controversies-and-urban-conversions.html
Knock John sea fort, one of several floating "Maunsell Forts," located in the Thames Estuary off the coast of England. Description from pinterest.com. I searched for this on bing.com/images
Flak tower - Wikipedia, the free encyclopedia