 Complete the following phrase:  Two further thousand-bomber raids were conducted over Essen and Bremen, but neither so utterly shook both sides as the scale of the destruction at Cologne and Hamburg. The effects of the massive raids using a combination of blockbuster bombs to blow off roofs and incendiaries to start fires in the exposed buildings created firestorms in some cities. The most extreme examples of which were caused by Operation Gomorrah, the combined USAAFRAF attack on Hamburg, 45,000 dead, attack on Kassel 10,000 dead, the attack on Darmstadt 12,500 dead, the attack on Pforzheim 21,200 dead, the attack on Swinemuende 23,000 dead and the 