The Morse code distress signal equivalent to mayday is SOS.
SOS is transmitted as three dots, three dashes, and three dots: … --- …. In formal Morse procedure, the sequence is sent continuously without spaces between the letters, making it a distinctive distress signal rather than an ordinary spelling of the word “SOS.”
The signal was standardized for maritime communication through international radiotelegraph regulations in the early twentieth century. It was selected because its pattern is simple, recognizable, and easy to transmit under difficult conditions. The letters were later used as a convenient mnemonic, although SOS was not originally an abbreviation for “save our ship” or “save our souls.”
Mayday serves the same basic distress purpose in spoken radio communication. It was adopted for voice transmissions in 1927 because Morse signals were unsuitable for speech. “Pan-pan” instead indicates an urgent situation that is not necessarily immediately life-threatening.