haroldnmod:

“Berlin flak protection

All around the capital in a wide arc lies a broad iron line of defense, the safe haven of the imperial capital from enemy attacks from the air. Day and night the men of the air defense, whether on anti-aircraft gun, searchlight, or listening device, are on the watch. We take photographs of the visit of our reporter to the anti-aircraft artillery.
Shown here: one of the giant listening devices that can capture even the slightest noise of an engine.”
(1939, via)