What is SOS in Morse Code?

As mentioned above, the distress signal is not actually the same as the letters "S.O.S.", so while it might be thought to mean "Save Our Souls" or "Save Our Ship" these are just ways to remember the code. In fact, when SOS was first introduced, American (or "Railroad") Morse code was still in use and in the American code three dashes represented the digit "5" so the distress signal was sometimes written as "S5S" (see picture).

By running different characters together, you can get the same sequence using many other letter combinations, such as <IWNI>, <IESEI>, <3B>, <V7> or even <EEETTTEEE>. It is likely that "SOS" was chosen to be the way to remember the signal just because it is simple and symmetrical. Coincidentally, now that SOS has moved from being purely a radio signal to more general signal, something which might be spelt out in large letters for a rescue plane to spot for instance, it is fortunate that the letters "SOS" read the same both ways up.

It is worth noting that the SOS distress signal is not the only one ever used in Morse code. The signal CQD was used by Marconi radio ("wireless") operators before SOS was introduced and both of these distress calls were signalled by the RMS Titanic for instance. In contrast to SOS, CQD was sent as three separate letters with spaces in between. The signal "CQ" is a general call for any station to respond, and "D" was added to indicate distress. The signal "CQ" is still used in amateur radio, but "CQD" is no longer used for distress.

The SOS distress signal was introduced by the German government in radio regulations which became effective on 1st April 1905. It became the worldwide standard under the second International Radiotelegraphic Convention, which was signed in 1906 and became effective on 1st July 1908. The convention adopted various regulations (including to use International, not American Morse code) with Article XVI stating that "Ships in distress shall use the following signal:   ▄ ▄ ▄ ▄▄▄ ▄▄▄ ▄▄▄ ▄ ▄ ▄  repeated at brief intervals" (see picture).

Other Ways to Send SOS

While the SOS distress signal is most commonly associated with Morse code radio transmissions, it can also be sent using other methods. For example, the signal can be sent using a flashlight by turning it on and off in the same pattern as the dots and dashes of the Morse code signal. This can be useful if you are stranded and need to signal for help at night. The player at the top of the page can show a flashing light if you press the "Light" button.