It is said that Mayday was selected and used in 1923 by Frederick Stanley Mokford, a senior officer of wireless communication at Creeden Airport in London, England. According to the current research, the earliest example of the word mentioned in the Oxford English Dictionary comes from the British newspaper The Times. The newspaper mentioned that Mayday is more popular as a distress signal than S.O.S "Because it is difficult to hear the letter S clearly on the phone".

Nan O 'S is used as a distress signal mainly for practical needs, while Mayday becomes an international distress signal (especially on ships and planes) mainly because of its language source. Although the appearance of this word may be related to May, it actually comes from the French word m'aidez or m'aider, which means "help".

Mayday is an international radiotelephone distress signal. The word Mayday was originally a French word m'aider to save me. This word is not used alone in standard French. It is usually expressed by Venez m'aider, but it is pronounced as Mayday in English.

Calling Mayday on the radio means encountering a real-time dangerous situation that threatens life. When sending a distress signal, you must call for three times in a row (distress, distress, distress) to avoid being heard, drowned by noise or confused with other communications. This must be noted.

Before the Mayday call sign appeared, SOS was a universal rescue Morse code. 1927 Washington international radiotelegraph convention clearly stipulates that "Mayday" is a distress signal. At present, the emergency frequency of aircraft is generally maintained at 12 1.5MHz (civil) and 243.0MHz (military). The transmission frequency of the early emergency positioning transmitter (ELT) was 406 MHz.