In the early days of the development of aviation, no requirement existed for communication between the aircraft and a ground station. Flying was carried out within sight of the ground or water, and the information required by a pilot was mainly visual. For example, navigation was carried out by the observation of well‐known landmarks and the direction of landing at an aerodrome was judged either from observation of a windsock or of a white letter T displayed in a Signals square. The approach to land was also by visual communication. A green lamp signal was an All Clear, and a red lamp signal advised the pilot to make another visual circuit before attempting to land. In extremis, when a red lamp signal had not been observed, the firing of a red Verey light usually achieved the objectiv