The Last Lion: William Spencer Churchill, Defender of the Realm, 1940-65

p. 198

In the early years of the WWII in Europe, Hitler thought he could force England into surrender by relentlessly bombing London and other English cities, always at night. He dropped three thousand bombs a week on England. Twenty per cent were duds, but Hitler had had German engineers figure out how to make the duds wickedly lethal. He wanted maximum terror even at the point of bomb disposal. So the engineers ”employed double fuses, one behind the other, so that the removal of the first triggered the unseen second. They installed fuses sensitive to light, so that the detonation sequence began when a squad opened the bomb, exposing the fuse to sunlight. Of all the detonator types, the time-delay fuse was the most terrifying. Because a mechanical time delay device would likely be damaged in the crash landing of the bomb, the Germans employed an acid drip that burned through a thin metal plate covering a secondary triggering mechanism. It was, said Churchill, ‘an especially effective agent in warfare, on account of the prolonged uncertainty it creates.’”