Night after night through six years of war, RAF Bomber Command's squadrons pounded away at the cities of Nazi Germany in a determined effort to bring the Third Reich to its knees. Pitted against Bomber Harris's aircrews and aircraft were some of the most effective and deadly defences the world has ever seen. For Bomber Command to launch a maximum effort raid on the Ruhr by night, or a low-level strike on an enemy target in occupied Europe by day, a huge amount of planning was involved.