The change came during the invasion of the Low Countries in May 1940, when the Germans surrounded the Dutch port of Rotterdam. The general in command of the 39th Panzer Korps told the Dutch defenders that unless they capitulated immediately the city would suffer ‘complete destruction’ by German bombers. ²⁸The following day, when negotiations between the two sides broke down, the Luftwaffe was dispatched to keep the general’s promise. Soon a hail of bombs was falling on the heart of the old city, setting large areas on fire. Later it became apparent that the Dutch garrison had surrendered before the air strike had taken place, but the order to recall the bombers came too late to save the city. That evening, while the houses still burned, the German Army entered Rotterdam just as they had entered Warsaw, unopposed.

The bombing of Rotterdam had sealed the Wehrmacht’s success in Holland, but it was a propaganda disaster for Germany. Over the next few days reports appeared across the world claiming that as many as thirty thousand civilians had been killed (although in reality the figure was more like a thousand). ²⁹Outraged, the British lifted some of their restrictions on bombing military targets inside Germany. On 15 May, the day after Rotterdam was bombed, Churchill sent ninety-nine bombers to attack rail and oil installations east of the Rhine. A few days later thirty were sent to attack the Blohm & Voss shipyards in Hamburg – the first of 213 attacks on the city. While a handful of bombs did hit the shipyards, in the darkness most fell in residential areas around the Reeperbahn, and thirty-four people were killed. The German press immediately hailed it as a ‘ruthless terror attack on the civilian population’. ³⁰

So began Britain’s strategic bombing campaign against Germany: a long-term systematic effort to destroy all German rail links, oil installations, airfields, armaments factories, metal foundries, stockpiles of raw material – in fact, anything of military value. Hitler responded, predictably, by ordering his air force to prepare for a full-scale air offensive against Britain, as a reprisal for the attacks on Germany and as preparation for a cross-Channel invasion of the British Isles. The battle for mainland Europe was over. The battle of Britain was about to begin.

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Britain was the last piece in Hitler’s jigsaw of western Europe, and his generals set about trying to conquer it in much the same way as they had conquered the rest of the continent. Their first task was to achieve command of the air, which meant destroying as many Royal Air Force planes and airfields as possible. Only after they had gained complete air supremacy would a cross-Channel invasion be possible.

When the Luftwaffe made their first bombing sorties over Britain in June 1940, an atmosphere of relative restraint still surrounded the bombing war. Hitler explicitly forbade his air force to attack London and other cities, partly because he had promised not to make war against women and children and partly because he wanted his forces to concentrate on the targets that mattered. ³¹At first the Luftwaffe attacked in daylight, but when German losses began to mount they were forced to switch to night attacks.

This was where both sides finally lost what was left of the mutual restraint with which they had started the war. In the dark, the German bombs increasingly missed their intended targets and fell on residential areas; then, on the evening of 24 August 1940, a dozen German bombers veered off course and accidentally dropped their bombs on central London. In retaliation, Churchill immediately ordered his bombers to attack Berlin. Although the raid caused little material damage it infuriated Hitler, who told a mass rally about ten days later, ‘If they attack our cities, we will simply erase theirs.’ ³²In reprisal for the Berlin attack, he ordered Hermann Goering to stop attacking purely military targets and concentrate on London.

There has been speculation that Churchill ordered the attack on Berlin deliberately to provoke this response in his enemy. The RAF was under serious threat at the time, and it was only after the Luftwaffe switched to area bombing that it could recover. If this was the case, then it was an expensive gamble. London suffered seventy-one major raids during the Blitz, and twenty thousand men, women and children lost their lives.

Attacks on towns across Britain soon followed. In November the Luftwaffe destroyed Coventry, and Hitler was so impressed that he coined a new verb, coventriren– ‘to coventrate’. Over the next six months the Luftwaffe attempted to ‘coventrate’ Birmingham, Liverpool, Manchester, Sheffield, Portsmouth, Plymouth, Bristol, Swansea, Cardiff, Glasgow and Belfast. Britain responded by targeting places in Germany where the centres of industry were surrounded by densely populated residential areas. The idea was that even if the factories were not destroyed, the homes of those who worked in them would be. If this was not officially a policy of ‘area bombing’, in practice that was exactly what it was. The pinpoint targeting of specific installations was simply not possible: from 15,000 feet, in the dark, it was considered accurate if an aircraft bombed within five miles of its aiming point. On 12 December 1940 the British government gave up all pretence when Winston Churchill ordered the bombing of Mannheim: for the first time the British had designated the city as the target, rather than anything specific within it. As the British official history of the bombing war points out, with the advent of such area bombing, ‘The fiction that the bombers were attacking military objectives in the towns was officially abandoned.’ ³³

It was an almost exact copy of what had happened in the First World War: a few piecemeal attacks, leading to a German offensive on Britain, and gradually the initial restraint exercised by both sides was whittled away to nothing. The only difference between the two wars was in scale. On 17 September 1940 alone the Luftwaffe unloaded more than 350 tons of bombs on London – more than the total dropped on the whole of Britain throughout the First World War. By the following April, they were able to drop more than a thousand tons of high explosive on the British capital in a single night. During the nine months of the Blitz more than forty thousand British people were killed, and a quarter of a million homes destroyed, leaving three-quarters of a million homeless. ³⁴All the terrifying pre-war predictions were beginning to come true.

And yet, in one respect, the prophets of air power seemed to have got it wrong. Contrary to the message preached by all the theorists before the war, the morale of the British people was not broken by the ordeal they had been through. If anything, they had become more determined, and their response to the bombings was vengeful rather than fearful. Politicians clamoured for retaliatory strikes against German cities; their speeches were echoed in the newspapers, which were filled with indignant leader columns requiring the RAF to fly to Berlin and give as good as Britain was getting. ³⁵

As Hitler turned his attention to Russia, and the raids on Britain petered out, the leaders of the bruised and battered RAF were given the space they needed to plan their revenge. The air force was still too weak to take the fight to the heart of the Reich, but it was obvious that Britain was now in the war for the long term. Over the next eighteen months the RAF would build its strength to create the most formidable bomber force the world had yet seen. Just as she had in the First World War, Britain now set her sights on a huge bombing campaign to destroy the German infrastructure. The only difference was that this time there would be no armistice to save the German people from British wrath.