SOS
SOS was developed from the general German radio call "SOE", with the 3 dits of a "S" easier to hear in static than the one dit of an "E". The string has no other meaning. It was also selected because it is easy to recognize and can be sent rapidly. Comparing SOS (di-di-di-dah-dah-dah-di-di-dit) with the older CQD (dah-di-dah-dit dah-dah-di-dah dah-di-dit) (— ·—· /—— ·—/—· ·) it is obvious how much simpler the new code is. It would not be mistaken for CQ,either. CQ is the radio code for "calling anyone" used in casual circumstances.