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Popham panel
Ground-to-air signaling device / From Wikipedia, the free encyclopedia
A Popham panel, or T-signalling panel, was a means of ground-to-air communication, in Morse code, developed during the First World War, before the introduction of radio communication. They were named for Robert Brooke-Popham and were used by the British and American armed forces.
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They were used in the Waziristan campaign of 1919–1920, and in the Kabul Airlift of 1928, and remained in use as a reserve method of communicating with aircraft as late as just before the Second World War. They were eventually rendered obsolete by the development of effective radio communication with aircraft.