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Manual · Note 03

SOS does not stand for anything

SOS was adopted in 1906 because the pattern three dots, three dashes, three dots is impossible to mistake for anything else, even through interference. It is sent as one continuous signal with no gaps between letters, so it is not really the letters S, O and S at all. Save Our Souls and Save Our Ship are backronyms invented later to explain a choice that was made purely on how the signal sounds.

Updated

Ask anyone what SOS stands for and you will get “Save Our Souls”, or “Save Our Ship”, or occasionally “Send Out Succour”. All three are inventions. The signal came first and the phrases were fitted to it afterwards.

Why this pattern

The delegates at the 1906 International Radiotelegraphic Convention in Berlin needed a distress call that could not be confused with anything else. Radio in 1906 was noisy, operators were inexperienced, and a call for help that could be misheard as ordinary traffic was worse than useless.

So they picked on sound, not meaning:

...---...

Three short, three long, three short. Nine elements in a strict symmetrical shape, with nothing else in the code that resembles it. Through interference, at the edge of readability, half-heard — it is still recognisable. That is the entire reason it was chosen.

It came into force on 1 July 1908.

It is one character, not three

This is the part that gets lost. SOS is a prosign: it is sent as a single continuous signal, with no gaps between what look like letters.

Written properly it has a bar over it — S̅O̅S̅ — which is the convention for “run these together as one character”.

That matters, because if you send it as three separate letters:

...   ---   ...

with proper three-unit gaps, you have sent the letters S, O and S. It is not wrong exactly, but it is not the distress signal, which is a nine-element shape with one-unit gaps throughout. Run together it lasts about two seconds at 15 WPM and has a completely different rhythm.

The same is true of the other prosigns you will meet. -.-.- is the “starting transmission” signal, not the letters K and A.

What it replaced

Before 1906 the Marconi company used CQD — -.-. --.- -.. — which is sometimes explained as “Come Quick, Danger”. That is also a backronym. CQ was (and remains) the general call to any station, usually said to come from the French sécurité; the D was simply appended for distress.

Both were in use for a while. The Titanic sent both in 1912, which is often retold as the moment SOS took over, though it had already been the standard for four years by then.

Why “Save Our Souls” stuck

Because it is useful. Nine elements are hard to remember; a phrase is easy. The backronym is a mnemonic that escaped and became a fact, which happens to a lot of things that are genuinely just arbitrary.

It is worth knowing it is a mnemonic, though, because the “it stands for something” framing leads people to send it as three letters — and the whole point of the signal is the shape.

Hear it

You can play SOS at any speed, or key it yourself on the telegraph and see whether your gaps hold together. Sending it as one unbroken character is harder than it looks, which is rather the point.