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SOS in Morse code

··· −−− ··· — three dots, three dashes, three dots, with no gaps between the letters.

Conversion
3 characters
Updates as you type
Letters split by spaces, words by /

Show the steps
  1. Each letter has its own pattern of dots and dashes. Letters are separated by a space and words by a slash.
  2. S → ...
  3. O → ---
  4. S → ...
  5. The commonest letters got the shortest codes: E is a single dot and T a single dash.

The light blinks in the lamp, never full screen, and stays under three flashes a second, so it runs at 7 WPM at most.

One signal, not three letters

Written down, SOS looks like the letters S, O and S. S is three dots and O is three dashes. Sent as a distress call, though, it goes out as one unbroken sequence of nine elements, with no letter spaces in it. Morse operators call a run-together signal like this a prosign.

The converter above spaces the letters, the same as for any other word. Type ...---... with no spaces and it reads that back as SOS. Press play to hear it, or flash it in the light box.

SOS to scale

As three letters · 34 unitsSOSgap 7As one prosign · 30 unitsSOSgap 70102030
One round of SOS to scale. A dot is 1 unit and a dash 3. Run together, the letters lose their 3-unit gaps.
One unitWords a minuteOne SOS, run togetherAs three letters
0.06 s201.8 s2.04 s
0.24 s57.2 s8.16 s
0.5 s2.415 s17 s
1 s1.230 s34 s
Count it out at
  1. On 0.06 s
  2. Off 0.06 s
  3. On 0.06 s
  4. Off 0.06 s
  5. On 0.06 s
  6. Off 0.06 s
  7. On 0.18 s
  8. Off 0.06 s
  9. On 0.18 s
  10. Off 0.06 s
  11. On 0.18 s
  12. Off 0.06 s
  13. On 0.06 s
  14. Off 0.06 s
  15. On 0.06 s
  16. Off 0.06 s
  17. On 0.06 s
  18. Off 0.42 s
  1. On 0.24 s
  2. Off 0.24 s
  3. On 0.24 s
  4. Off 0.24 s
  5. On 0.24 s
  6. Off 0.24 s
  7. On 0.72 s
  8. Off 0.24 s
  9. On 0.72 s
  10. Off 0.24 s
  11. On 0.72 s
  12. Off 0.24 s
  13. On 0.24 s
  14. Off 0.24 s
  15. On 0.24 s
  16. Off 0.24 s
  17. On 0.24 s
  18. Off 1.68 s
  1. On 0.5 s
  2. Off 0.5 s
  3. On 0.5 s
  4. Off 0.5 s
  5. On 0.5 s
  6. Off 0.5 s
  7. On 1.5 s
  8. Off 0.5 s
  9. On 1.5 s
  10. Off 0.5 s
  11. On 1.5 s
  12. Off 0.5 s
  13. On 0.5 s
  14. Off 0.5 s
  15. On 0.5 s
  16. Off 0.5 s
  17. On 0.5 s
  18. Off 3.5 s
  1. On 1 s
  2. Off 1 s
  3. On 1 s
  4. Off 1 s
  5. On 1 s
  6. Off 1 s
  7. On 3 s
  8. Off 1 s
  9. On 3 s
  10. Off 1 s
  11. On 3 s
  12. Off 1 s
  13. On 1 s
  14. Off 1 s
  15. On 1 s
  16. Off 1 s
  17. On 1 s
  18. Off 7 s

The last gap is the pause before you start the next SOS.

How the timing works

Morse is timed in units. A dot lasts one unit and a dash three, with one unit of silence between the marks inside a letter. Letters are three units apart and words seven. One unit lasts 1200 divided by the speed in words a minute, in milliseconds, so it's 60 ms at 20 words a minute.

Sent as three letters, one SOS and the pause after it take 34 units. Run together, it takes 30. With a torch or a whistle there's no machine keeping time, so pick a unit you can count steadily and keep every dash three times as long as a dot. Then stop for seven units before you start again.

Where SOS came from

Germany got there first. Its radio regulations, in force from 1 April 1905, listed three signals, and the distress one, the Notzeichen, was SOS. The international version came from Berlin, where a radiotelegraph convention was signed on 3 November 1906 and took effect on 1 July 1908. Its service regulations told ships in distress to send the signal, repeated at brief intervals.

Not everyone switched at once. In 1904 the Marconi company had told its operators that ships in distress should call CQD. The earliest ship reported to have sent SOS was RMS Slavonia, off the Azores, on 10 June 1909. When the Titanic sank in April 1912 her operators sent both CQD and SOS. After that, CQD seems to have died out.

In 1927 the International Radio Convention adopted Mayday as the spoken equivalent. SOS stayed the radio distress signal at sea until 1999, when the Global Maritime Distress and Safety System replaced it.

It doesn't stand for anything

SOS began as a distinctive Morse sequence, not as an abbreviation. Save our souls and save our ship are backronyms, made up for it later in popular use.

SOS today

From Annex IV of the International Regulations for Preventing Collisions at Sea, as amended in 2009.
SignalWhat Annex IV says
SOSA signal made by any signalling method consisting of the group ··· −−− ··· (SOS) in the Morse Code
MaydayA signal sent by radiotelephony consisting of the spoken word MAYDAY
N.C.The International Code Signal of distress indicated by N.C.
ArmsSlowly and repeatedly raising and lowering arms outstretched to each side

Any signalling method

The wording in the collision regulations is broad. A lamp, a horn, a mirror flash or a radio all count, as long as the pattern is SOS. The same annex prohibits using any of its distress signals except to show distress and the need for help. Practise with this page's sound and light box, not on the water.

On land, mountain distress signals work differently. They're based on groups of three, or six in the UK and the Black Forest. There you give six signals within a minute, pause for a minute and keep repeating until rescue arrives, and rescuers answer with three a minute.

Questions

What is SOS in Morse code?

··· −−− ···, three dots, three dashes and three dots. As a distress call it's sent as one run, with no gaps between the letters.

Does SOS stand for save our souls?

No. It started as a distinctive Morse sequence with no meaning of its own. Save our souls and save our ship came later.

When did SOS become the distress signal?

Germany used it from 1 April 1905. The Berlin radiotelegraph convention made it international, signed on 3 November 1906 and in force from 1 July 1908.

Is SOS still used?

Morse radio distress calls at sea were replaced by the Global Maritime Distress and Safety System in 1999. SOS by any signalling method is still listed as a distress signal in the collision regulations.

How do I flash SOS with a torch?

Three short flashes, three long, three short, each long one three times the length of a short one. Keep the gaps inside the signal as long as one short flash, then wait seven before repeating. The count-out above gives the steps in seconds.

What is the difference between SOS and Mayday?

SOS is the Morse signal. Mayday is the spoken one, adopted in 1927 for voice radio.

Sources

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