SOS in Morse Code: What It Means and Why It’s ... --- ...
The real history of SOS: why it was chosen in 1906, what it does and doesn’t stand for, its role on the Titanic, and how to tap or flash it correctly.
Three dots, three dashes, three dots. SOS is the most recognisable piece of Morse code in the world, known even to people who could not send a single other letter. But almost everything the average person believes about it is slightly wrong. It is not an abbreviation. It was not first used on the Titanic. And technically, it is not even three letters. Here is the true story, along with how to send it if you ever need to.
SOS does not stand for anything
“Save Our Souls”, “Save Our Ship”, “Send Out Succour”: all of these are backronyms invented after the fact. SOS was chosen purely because of how it sounds and how it looks on paper. The sequence di-di-dit dah-dah-dah di-di-dit is unmistakable, easy to send even under stress, impossible to confuse with ordinary traffic, and recognisable to an operator who catches only part of it. The letters S and O were simply the names people attached to the pattern afterwards.
Strictly speaking, SOS is a prosign: a single continuous signal sent with no gaps between the three groups. Written properly it has a bar over the top, SOS with an overline, to show it is one symbol rather than three separate letters. In practice, though, nearly everyone sends and describes it as S-O-S, and it works either way.
Where SOS came from: Berlin, 1906
In the first years of wireless telegraphy there was no agreed distress call. The Marconi Company, which dominated maritime radio, introduced CQD in 1904: CQ was the general call to all stations, and D was added for distress. Meanwhile Germany had adopted its own signal in its 1905 radio regulations: the three-dots-three-dashes-three-dots pattern, referred to there as the “Notzeichen” or distress sign.
When delegates from around the world met at the International Radiotelegraph Convention in Berlin in 1906, they chose the German signal as the international standard. The agreement came into force on 1 July 1908. Some sources suggest the pattern was picked partly because it could be sent rapidly and repeated indefinitely without ambiguity, and partly because the German system was already in use. British Marconi operators were slow to give up CQD, and for several years both signals were heard at sea.
SOS and the Titanic
The popular story that SOS was first used by the Titanic in April 1912 is false, but there is a grain of truth in it. The first recorded SOS is usually credited to the Cunard liner Slavonia, which ran aground near the Azores in June 1909, and there are claims of even earlier uses by German ships. Titanic’s operators, Jack Phillips and Harold Bride, initially sent CQD, as was Marconi practice. According to Bride’s later account, he suggested to Phillips that he try the new call as well, joking that it might be his last chance to send it. So Titanic sent both CQD and SOS, and the enormous publicity around the sinking did more than any convention to make SOS the signal everyone knew.
The radio drama of that night, with the nearby Californian’s operator having gone to bed and the Carpathia steaming through ice to reach the survivors, led directly to new rules requiring 24-hour radio watches on passenger ships.
How to tap SOS
Because it is a single continuous signal, SOS is one of the easiest things to send correctly, but the timing still matters. Follow the standard Morse ratios: a dash is three times as long as a dot, and the gap between each element is one dot length. Do not leave a longer gap between the S and the O, since the signal is meant to run together.
- Three short taps: tap, tap, tap.
- Three long taps, each about three times longer than a short one: taaap, taaap, taaap.
- Three short taps again: tap, tap, tap.
- Pause for about the length of seven dots, then repeat. Keep repeating until someone responds.
Tapped on a pipe, a wall or a hull, the difference between short and long is conveyed by the gap after each tap rather than the tap itself, so exaggerate the pauses: three quick, three slow, three quick. Rescuers are trained to listen for that rhythm.
How to flash SOS with a light
With a torch, phone flashlight or signal lamp, cover or switch the beam off between elements. Three short flashes, three long flashes, three short flashes, pause, repeat. If you can aim the light, sweep it slowly across the horizon so a distant observer is more likely to catch it. At night a flashing light is visible much further than a steady one, and the unnatural rhythm of SOS is what makes it stand out from ordinary lights.
Other ways people send SOS
- Written in the sand, snow or on a rooftop in large letters. SOS reads the same upside down, which is part of its appeal for ground-to-air signalling.
- Three of anything: three fires, three whistle blasts, three gunshots. The “rule of threes” in wilderness signalling comes from the same tradition.
- Many smartphones include an emergency SOS feature, and some flashlight apps flash the pattern automatically.
Is SOS still official?
Not at sea. In 1999 the Global Maritime Distress and Safety System (GMDSS) fully replaced Morse for international shipping, and SOS ceased to be the official maritime distress signal. Ships now use automated digital calls and satellite beacons. Even so, SOS remains universally recognised, is still taught in survival courses, and is still the right thing to send if a light or a tapping sound is all you have. Nobody who hears three short, three long, three short will wonder what you mean.
Related signals worth knowing
SOS is not the only emergency code from the Morse era. CQD, as mentioned, was its predecessor. The spoken radio equivalent is “Mayday”, from the French “m’aidez” (“help me”), adopted in the 1920s for voice. “Pan-pan”, from “panne” (breakdown), signals urgency without immediate danger. In Morse, the prosign for urgency was XXX and the safety signal was TTT. You can read about prosigns and the rest of the operator’s shorthand in our guide to numbers, punctuation and prosigns.
If you would like to hear SOS and other words played at real speed, try the Morse translator. And if you want to go beyond the one signal everyone knows, our beginner’s guide will get you copying full sentences by ear.
