H2S: an airborne radar navigation and bombing aid

H2S is a microwave radar device which operates to provide in an aircraft a visual picture of the terrain beneath it, enabling accurate navigation and bombing to be carried out from above cloud. The basis of the system is the manner in which radar ground responses vary with the characteristics of the ground producing them, towns, especially, standing out against the background. The historical development of H2S is described from the first recognition of its possibility in 1939 up to the present time. An account is given of the special problem which had to be solved, including the development of aerial systems which eliminate between desired limits the effect of range on the amplitude of the radar response and the production of a suitable display with correction for slant-range distortion so as to provide a true plan-picture of the ground beneath the aircraft. An outline is given of the method of use of the equipment by Bomber Command of the Royal Air Force, and the paper concludes with a description of a complete H2S equipment.