During World War II, Leipzig was repeatedly attacked by British as well as American air raids. The most severe attack was launched by the Royal Air Force in the early hours of 4 December 1943 and claimed more than 1,800 lives. Large parts of the city center were destroyed, while factories experienced temporary shortfalls in production, had to move production facilities or even were decentralized. At the outbreak of the war, Leipzig had more than 700,000 inhabitants and was therefore the sixth-largest city of the “Greater German Reich” (including Vienna). Leipzig additionally had significance by hosting the leading trade fair of the German Empire. The Erla Maschinenwerk aircraft factory that produced Messerschmitt Bf 109 fighter planes at the three locations of Heiterblick, Abtnaundorf and Mockau were important for warfare. Additionally, Leipzig was an important railroad intersection in Germany at that time. Attacks First attacks Prior to 1942, Leipzig had been considered relatively safe from potential aerial assaults because of the long flight route from Britain. But after the attack on Kassel on 22–23 October 1943, it became clear that British bombers were able to reach central Germany. On 27 March 1943, bombs were dropped by British aircraft setting Gohlis on fire. In the night of 31 August to 1 September, the British RAF Bomber Command carried out minor attacks on the towns of Eutritzsch and Schönefeld causing four casualties. 4 December 1943 During the night of 2 December 1943, the Royal Air Force once again attacked Berlin. Meanwhile, the German night fighters had prepared for these attacks and were able to shoot down 40 bombers. The following night, Leipzig was the target of an attack. The air route of this attack had been planned in a way to keep the German Air Defense in the dark about the attack's objective for as long as possible. Because the Germans did not expect an assault at this time, the Royal Air Force launched its attack in the early morning hours. The route the bomber squadrons were following crossed over the continental coastline at the Zuiderzee, continued eastwards to Northern Germany and Berlin and turned southwards over the area of the city of Brandenburg. Between 3:50 AM and 4:25 AM, 442 bombers dropped a total amount of almost 1400 tons of explosives and fire bombs. At 3:39 AM, the air raid warning had been raised, with the all-clear following at 5:39 AM. In