'What's Your Sign?'

摘要

Gradually the use of W/T (wireless telegraphy—Morse code transmissions) and R/T (radiotelephony, or voice communication) became increasingly common in Europe as air traffic control (ATC) developed to safely expedite air transport and provide navigation support. The development of radar (radio, detection, and ranging), radio, and navigation during World War II led to increasing ATC sophistication.