Norden bombsight
Although the need for an improved CSBS was known in the 1930s, little work on developing such a sight was carried out. That was because an entirely new class of tachometric bombsights were being developed, which offered dramatically improved accuracy and automated much of the setup. The RAF was working on such a design, the Automatic Bomb Sight, but development was slow and it had not been accepted for use when the war started. Learning of a similar design developed by the US Navy, the Air Ministry began extensive negotiations in an effort to gain a production licence for this Norden bombsight. The US Navy constantly refused these requests, deeming it too sensitive to risk losing over Germany, and their refusals ultimately led to significant political friction between the two nations. Ironically, the plans of the Norden bombsight had been passed to the German military by a US-based spy in 1938.