When the Blitz began, the government cut power to make it harder for Germany to bomb. Street lights, car headlights and lighting signs were switched off. People hung black curtains on their windows so that light could not be seen outside their houses. When a bomb attack is imminent, air raid sirens are triggered to warn. Another defensive measure used by the British was the installation of barrage balloons in and around the main target areas of the attack. These balloons, the largest at about 60 feet (18 m), were essentially airspace denial devices. These balloons prevent low-flying aircraft from...