XIV was theoretically less accurate than the contemporary Norden bombsight. Britain was interested in the Norden bombsight. He donated a once-top-secret Norden Bombsight to the CAF's B-29 bomber restoration project. To improve bombing accuracy, the Vimy was equipped with the High Altitude Drift Mk.1a bombsight. The two American airmen are interrogated for information about newer bombers and the Norden bombsight. Norden's first attempt at an improved bombsight was actually an advance in PDI design. The best known United States device was the Norden bombsight. Developments such as the Norden bombsight further fueled these concerns. Expansion of Norden bombsight production to a final total of six factories took several years. In 1920, he started work on the Norden bombsight for the United States Navy. The pilot of bomber versions was provided with a telescopic bombsight. For their needs they developed a new vector bombsight, the Mk. Lieutenant Frederick Entwistle, the Navy's chief of bombsight development, judged it revolutionary. The first bombsight was produced in 1927. It had dual controls and was fitted with a locally designed bombsight and a camera.