Jet propulsion opened the door to the ultimate bomber aircraft. Though the precise value of the bomber has been the subject of intense debate, it is agreed that the bomber, particularly during WW II, was a source of great terror and horror. It was targeted at entire cities, leveling them to the ground and in the process killing thousands of civilians. Post WW II German estimates of the bombings counted 593 thousand civilians killed and 3.3 million buildings razed. Yet between 1941 and 1944, German war production rose five-fold on average. Despite the destruction, the German war machine churned on.