A fire storm during a bombing raid had effects comparable to the explosion of an atomic bomb. The first one took place in a British attack on Hamburg in July 1943. The target was well marked by Pathfinders and 'window' (metallised strips of paper) was dropped, which interfered with the German radar. Roofs in German towns were treated with fire-proofing chemicals but the RAF method was to use high explosives to tear them apart and drop thousands of tonnes of fire bombs, many of them liquid, to start fires at the bases of buildings. In Hamburg, a huge central fire sucked in air at hurricane force speeds and merged with lesser fires until a single, vast fire engulfed an area 5.5km by 4km. People found it difficult to move in the streets against the winds and some got sucked into the fire. Police and firemen could not get many to leave their cellars, where they were burnt, probably dying first of carbon monoxide poisoning. A layer of ash in one shelter was estimated to be the remains of 250 or 300 people. Many people plunged into canals and harbour waters for protection. Altogether, 50 000 people were killed in Hamburg as many as were killed in all the German raids on Britain-and a million fled the Eighty-six bombers were shot down. It was said that six more such raids would knock Germany out but it proved difficult to repeat such a concentration of bombing. The other famous firestorm was in the medieval half-timbered city of Dresden in 1945, which has been criticised as unnecessary. Perhaps 50000 people were killed there, perhaps double that.