At 1.47 a.m. the last of the attacking aircraft dropped its mix of high explosives and incendiaries, and the tail end of the bomber stream made its way back towards the coast and over the North Sea to England. Behind them they left one of the biggest man-made fires the world has ever seen, still growing in intensity. As a young rear gunner wrote in his diary that night: ‘If it had been a really clear night the fires would have been visible nearly back to our coast. As it was we could see it nearly half-way back, about 200 miles, and a column of smoke about 20,000 feet, so Hamburg must have had it.’ 25
16. Firestorm
What if the breath that kindled those grim fires
Awaked should blow them into sevenfold rage
And plunge us in the flames?… what if all
Her stores were opened and this firmament
Of hell should spout her cataracts of fire
John Milton, Paradise Lost 1
To understand what happened on the night of Tuesday, 27 July 1943, one needs to know a little about how major fires work. Few people have any direct experience of conditions inside a major conflagration, and even those unlucky enough to have lived through a house fire cannot possibly understand what it is like to be caught in a firestorm.
Large conflagrations are different from house fires in two important respects. First, because of their sheer size they produce such vast quantities of smoke that even those far away from the flames may suffocate. This is particularly dangerous in city fires – anyone sheltering in the confined space of a basement or cellar risks death from smoke inhalation or carbon monoxide poisoning, as all the oxygen is sucked out of the air and replaced with poisonous fumes.
Second, and more importantly, the incredible temperatures such fires reach – sometimes as high as 800°C – superheat the air above and around the fire, causing it to rise rapidly. In some cases this sets off a chain reaction. As air rushes skywards it leaves a vacuum, which sucks new air from the surrounding areas to fill it. The new air brings oxygen, which feeds the fire. The process accelerates: the fire gets hotter, and the winds get faster, often reaching speeds of 60 or 70 m.p.h. This is what gives the ‘firestorm’ phenomenon its name: the combination of huge fires and storm-force winds. As long as there is enough fuel to keep the fire burning the winds will continue to blow, first rushing into the fire horizontally along the ground, then shooting skywards with the heat.
As I mentioned in Chapter 10, Hamburg had already had a firestorm on Saturday night, where witnesses claimed to have seen ‘a frightful storm, caused by the heat’, and winds so strong that it was impossible to fight one’s way through them. 2On that night British air crew reported seeing clouds of smoke billowing up to 20,000 feet and beyond, forced rapidly into the sky by the heat. This was comparable to the devastating firestorm that had enveloped Wuppertal two months before the Hamburg bombings, and that would consume Dresden eighteen months later. 3
What happened on the night of 27 July, however, was in a different league. The winds reached speeds of at least 120 m.p.h., and in places perhaps as high as 170 m.p.h. 4To make things worse, they were not steady in their force: they swirled and changed direction from one moment to the next. In a forest firestorm the wind is generally free to take the most direct route to the centre of the conflagration, spiralling inwards in an anti-clockwise direction, like a cyclone. By contrast, in a city like Hamburg, the winds are forced away from their natural course by all the buildings that stand in the way. That night they were channelled along streets, sometimes meeting head-on at junctions, causing eddies and swirls that knocked people off their feet. There are many reports of ‘fire-whirls’ at such junctions – miniature tornadoes – which added to the misery of the fugitives trying to reach safety. 5
Some of the hottest temperatures ever experienced in a city fire accompanied the hurricane-force winds. The sheer amount of flammable material, stacked up in six-storey buildings, like huge charcoal ricks, produced enough heat to melt the glass in the windows of cars and trams on the streets – which means the temperature must have approached glass-furnace level, about 1,400°C. 6Inside the buildings it was even hotter – cutlery and glass bottles melted, and bricks burned to ash.
In the years that followed the catastrophe, the Hamburg fire-storm came under intense scientific scrutiny, and it was concluded that no other large fire in recorded history has ever equalled its intensity. It was far worse than any of the great forest fires that have engulfed large parts of America and Canada; greater even than the fires that have consumed London, Chicago or any other city bombed by the Allies across Germany.
The reason Hamburg’s firestorm was so bad is as simple as the result was tragic: weather conditions – a set of circumstances so unusual for the area that they have only rarely been repeated since. Because of all the hot, sultry weather Hamburg had been experiencing, an unstable pocket of warm air was sitting directly over the city. It had been warmed by all the fires that had been burning since Sunday, and was saturated with smoke particles, which retained the heat even more effectively. All around Hamburg, however, and high above it, the air was much cooler. Surrounded on all sides by this colder air, the pocket of warm air was like a huge, pressurized balloon, sticking up some 10,000 feet. All it would take to burst the top off this balloon was a sharp rise in temperature. Once it hadburst, the warm air over the city would rise unrestricted for thousands of feet, rapidly drawing newer air behind it, and setting off the greatest firestorm the world has ever seen. 7
The final factor was the humidity – or, rather, the lack of it. Because the city is close to the sea, the air in Hamburg normally has a very high humidity – a seasonal average of about 78 per cent. On 27 July 1943 the humidity was a mere 30 per cent. After the long, dry summer most of the buildings in Hamburg were like tinder, but with such low humidity there was nothing to stop the rapid spread of fire. Other historians have used the analogy of a furnace with a very tall chimney, just waiting for someone to light a match. 8That match was lit shortly before 1.00 a.m. when the RAF dropped the first of 1,174 tons of incendiaries into the eastern quarter of the city.
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Part of the tragedy for Hamburg was the sheer bad luck of it all. The Allies had not planned specifically to take advantage of the prevailing weather conditions; indeed, they did not even realize that such conditions couldlead to a firestorm. 9Their understanding was far more basic: the weather was good because it was clear, which made navigation to the city much easier, and because it was dry, which would make it easier to start effective fires. They had no idea quite how perfect the conditions were for their purpose.
They did, however, have a good idea of how to start fires, and how to keep them going. After years of practice, they had created a highly effective system. To start with, they knew that the most important factor was concentration. If an attacking force dropped its incendiaries in a single area it would be impossible for the defenders to put out all of the fires. If enough were allowed to take hold, they would soon join up into huge conflagrations. The fire services would be unable to cope: they would be forced further and further away from each fire’s centre, and would struggle to prevent them spreading to other districts.