the reasons daylight bombing was considered. The Germans had also studied this problem and had invested considerable effort in radio navigation techniques to address this, demonstrating a standard of bombing accuracy during the night raids that daylight forces found difficult. The RAF lacked similar navigation systems, having ignored their development for a number of years, and relied almost entirely on dead reckoning and optical instruments such as the Course Setting Bomb Sight. In limited visibility conditions or when the target did not have a clearly distinguishing landmark, accurate bombing was very difficult. Bomber Command pressed ahead with a night bombing campaign starting in 1940. Bomber crews reported good results, turning for home if they lost their way or could not find the target due to weather, and pressing on only if they felt confident they could identify the target with certainty. However, it was not long before reports started reaching the UK from observers on the ground reporting that the bombers were never even heard over the targets, let alone dropping their bombs nearby. At first these reports were dismissed, but as other branches of the UK armed forces complained, a report was commissioned to answer the question. The result was the Butt Report of 18 August 1941, which noted that by the time the aircraft reached the Ruhr, only one in 10 ever flew within five miles of its target. Half of all the bombs carried into combat and dropped—many returned undropped—fell in open country. Only 1% of all the bombs were even in the vicinity of the target. Clearly something had to be done to address this or, as the other forces suggested, the strategic campaign should simply be dropped. Around this time Frederick Lindemann wrote an infamous report on dehousing, suggesting that the bomber force be directed against German urban areas, destroying as many houses as possible and thus rendering the German workforce unable to work effectively. Accepting the recommendations of Lindemann's report after intense debate, the British began planning a major offensive starting in the spring of 1942 with the express aim of destroying German cities. Also, by 1940 the British had started development of a number of night navigation aids, and were already testing the Gee hyperbolic navigation system on combat missions. These would be available in quantity in early 1942, just as the first of the new heavy bombers, the Avro Lancaster and Handley