'W.T. 174 Information A.I. MK.III in Blenheim Fighter'. Published by the Air Ministry in July 1940. Secret file, approximately 22 x 34cm. 28 pages plus approximately 32 pages of photos/pull-put diagrams. This covers the use of 'Airborne Interception' (A.I.) in the Bristol Blenheim developed to detect and track other aircraft within 8,000 feet of it. A.I. was essentially the birth of RADAR. The installation in the Blenheim was intended to enable an operator to guide a pilot from the position given by the ground station to the point within visual range of his 'target'. The manual gives an introduction on the principles of A.I., explains the transmitting and receiving equipment, its operation and interpretation of images. Servicing and maintenance is also covered. The numerous diagrams and photos illustrate the equipment and typical 'pictures' that might be received. The paper cover is worn and dog-eared with ragged edges and corners. Inner pages are soiled but in sound condition. The early use of Airborne Interception Radar had a significant beneficial effect on the effectiveness in intercepting German bombers during the Blitz. An extremely rare document. Stock code P22509.