Radio or ‘wireless’ was first used aboard ships early in the 20th century. The wireless signal itself was just the carrier for telegraph and telephone messages through the ether. Telegraphy was sent via Morse code and telephony was done by voice. In those early years, most ship to shore and intership communication was done by telegraphy.
Maritime distress signals of that era developed from the telegrapher’s lexicon.
Many of the new shipboard telegraphers who worked in the ‘radio shack’ began their careers as postal or railroad Morse code operators ashore. As a consequence, the first maritime telegraphic distress signals reflected that heritage. The code letters ‘CQ’ were a general call used on land telegraph lines and, in 1904, the Marconi Wireless Company tacked on a ‘D’ to that for ships. From that time on, ‘CQD’ was the Morse code signal for ‘All stations, Distress’ and specifically used for ships.
It was the Marconi operator aboard the Titanic who, in 1912, relayed that disaster to all ships at sea and the rest of the world using ‘CQD’.
As an extra measure, the Titanic’s radio officer also interspersed his repeated distress calls with the less well-known telegraphic SOS. Germany had been using SOS for ship distress calls since 1905, but it was not widely adopted. Even though many sailors believe it stands for ‘Save Our Ship’ or ‘Save Our Souls’, it was selected purely because of its unmistakable character as a Morse code sequence. That easily recognizable dit-dit-dit dah – dah – dah dit-dit-dit, meant that receiving stations were to immediately cease handling all other traffic and quickly answer that distress signal.
Voice communication between vessels by radio didn’t become commonplace until World War II, when the precursor of VHF radio was used for direct bridge-to-bridge conversations.
It was known as TBS or ‘Talk Between Ships’. The international marine VHF channels, as we know them today, were codified in 1959 by the International Telecommunication Union, at a time when megahertz were known as ‘megacycles per second’.
Between World War I and World War II, the telegraphic SOS became the defacto maritime distress call.
In addition, XXX was used as an urgent signal, being less urgent than SOS. XXX was used when there was concern for the safety of a ship or the safety of person on board. TTT was used as a safety signal to precede ice, storm and other navigational warnings including coastal artillery practice.
For a voice distress call, instead of using SOS, VHF marine radio protocol adopted the word ‘Mayday’.
This is the Anglicized pronunciation of the French m’aidez, or ‘help me’. The voice equivalent of XXX became the word ‘Pan’. That corresponded to the French pronunciation for panne, which means ‘breakdown’. And TTT was replaced by ‘Security’, using the phonetic French ‘Securitay’. The French word sécurité translates into ‘safety’.
When is Mayday used?
The regulatory definition of ‘distress’ is that “a vessel, vehicle, aircraft or person must be in grave or imminent danger.” And it is solely the judgment of the person in charge of the vessel in distress, whether the ‘grave and imminent’ scenario is met.
The voice procedure for a Mayday is divided into two parts, the distress call and the distress message, both transmitted in sequence on Channel 16 at high power. “The distress call is the initial ‘shout for help’, intended to alert listeners to the coming message. The distress message conveys important information to potential rescuers.” The distress call is simple. It is “Mayday” spoken three times slowly and clearly, followed by “this is” and the name of the vessel said three times. The vessel’s radio call sign and Maritime Mobile Service Identity (MMSI) number, spoken once, round out the call.
The distress message is a slightly more complex.
With the high stress levels triggered by an emergency, it is helpful to have a tool for remembering all the bits that are part of the Mayday message. The mnemonic device “MIPDANIO” fits the bill nicely:
M – Mayday
I – Identity
P – Position
D – Distress
A – Assistance
N – Number
I – Information
O – Over