Distress signal

SOS in Morse code

Three short, three long, three short: ▶ Listen – the world’s best-known signal is not a word but a sound pattern.

What SOS means – and what it does not

SOS is not an abbreviation. “Save Our Souls” and “Save Our Ship” are backronyms invented later. The signal was chosen because its pattern is easy to send, easy to recognise and impossible to confuse with anything else – even in poor conditions. Strictly speaking it is not the letters S, O, S but a single continuous sign, ···–––···, sent without the usual gaps between letters.

History: from CQD to SOS

In the early years of radio there was no common distress signal. In 1904 the Marconi company introduced CQD – CQ, the general call, plus D for “distress”. Other countries used their own signals. At the International Radiotelegraph Conference in Berlin in 1906, SOS was agreed as the international distress signal; the rule came into force in 1908.

The change became famous on the night of 14–15 April 1912. After hitting an iceberg, the Titanic first sent CQD with its call sign MGY. Operator Harold Bride suggested to Jack Phillips that they also send the still fairly new SOS. The Carpathia heard the call, headed for the scene and rescued around 700 people from the lifeboats that morning. Afterwards, radio rooms on passenger ships had to be staffed around the clock.

SOS today

Since 1999 Morse is no longer required for maritime distress communication; the Global Maritime Distress and Safety System (GMDSS) relies on satellites and digital radio. SOS is still understood worldwide – and works with anything you can switch on and off.

Sending SOS with light, sound or knocking

• Torch or phone light: three short flashes, three long, three short. A long flash should last about three times as long as a short one. Then a clear pause, and repeat.
• Whistle or horn: the same pattern as short and long blasts.
• Knocking: knocks have no length, and there is no fixed rule. What matters is a recognisable pattern: three alike, three clearly different (for example double knocks), three alike – then a pause.

In a real emergency, always use official emergency numbers first if you can (112 in Europe, 911 in North America). Morse is the fallback when nothing else works.