No one had any doubt that the bombers would come. Defense planning began well before the war, though the planners had no specific threat in mind. Europe was Europe. If past experience was any sort of guide, a war could break out anywhere, anytime. Britain’s military leaders saw the world through the lens of the empire’s experience in the previous war, the Great War, with its mass slaughter of soldiers and civilians alike and the first systematic air raids of history, conducted over England and Scotland using bombs dropped from German zeppelins. The first of these occurred on the night of January 19, 1915, and was followed by more than fifty others, during which giant dirigibles drifting quietly over the English landscape dropped 162 tons of bombs that killed 557 people.

Since then, the bombs had grown bigger and deadlier, and more cunning, with time delays and modifications that made them shriek as they descended. One immense German bomb, a thirteen-foot, four-thousand-pounder named Satan, could destroy an entire city block. The aircraft that carried these bombs had grown larger as well, and faster, and flew higher, and were thus better able to evade home-front defenses. On November 10, 1932, Stanley Baldwin, then deputy prime minister, gave the House of Commons a forecast of what was to come: “I think it is well for the man in the street to realize that there is no power on earth that can protect him from being bombed. Whatever people may tell him, the bomber will always get through.” The only effective defense lay in offense, he said, “which means that you have to kill more women and children more quickly than the enemy if you want to save yourselves.”

Britain’s civil defense experts, fearing a “knock-out blow,” predicted that the first aerial attack on London would destroy much if not all of the city and kill two hundred thousand civilians. “It was widely believed that London would be reduced to rubble within minutes of war being declared,” wrote one junior official. Raids would cause such terror among the survivors that millions would go insane. “London for several days will be one vast raving bedlam,” wrote J.F.C. Fuller, a military theorist, in 1923. “The hospitals will be stormed, traffic will cease, the homeless will shriek for help, the city will be a pandemonium.”