SOS in Morse Code

Timing at 20 WPM

International Morse timing is measured in units: a dot is 1 unit, a dash 3, the gap inside a character 1, the gap between letters 3 and the gap between words 7. At 20 words per minute, one unit is 1200 ÷ 20 = 60 ms.

As separate letters, SOS would take 27 units (1.62 s). Sent correctly as one continuous signal, the letter gaps become 1-unit element gaps, so it takes 23 units — 1.38 seconds at 20 WPM: 6 dots and 3 dashes.

Sound it out

Operators learn Morse as sound, not as dots to count. Say “di” for a dot inside a character, “dit” for a final dot and “dah” for a dash, running the whole signal together:

di-di-di-dah-dah-dah-di-di-dit

Letters in SOS that are easy to mix up

These letters differ from the ones in SOS by a single dot or dash — one flipped element, or one extra or missing at the end — so they are the usual misreadings when you are copying by ear or by light:

About SOS

SOS is the international radiotelegraph distress signal. It is sent as a single unbroken character — three dots, three dashes, three dots — with no gaps between the S, O and S, which is why operators write it with a bar over the letters or as the prosign <SOS>. Written out as three separate letters it takes longer and could be mistaken for ordinary text.

The ITU's history of the 1906 International Radiotelegraph Conference in Berlin records that the conference gave priority to the SOS distress signal (···−−−···); the convention signed there came into force on 1 July 1908. Some histories, including one published by the International Maritime Organization, date its international adoption to the London conference of 1912, which followed the Titanic disaster; before then the Marconi company's CQD was also in wide use.

Despite the popular expansion 'Save Our Souls', SOS is not an abbreviation. The IMO notes that the letters have no special significance except that the pattern is easy to remember and transmit. Morse distress working at sea ended when the satellite-based Global Maritime Distress and Safety System (GMDSS) became fully operational on 1 February 1999, but SOS is still recognised everywhere — including when flashed with a light or tapped out by hand.

SOS in other codes

Convert your own text with the Morse code translator, the NATO alphabet converter or the binary translator, or print the Morse code alphabet.

Sources

• ITU — International Radiotelegraph Conference (Berlin, 1906)
• Radiotelegraphic Convention signed at Berlin, 3 November 1906 (UK Treaty Series), Article 22: in force 1 July 1908
• IMO — Search and Rescue and the GMDSS (1999)